Chevy, GMC & Cadillac DTC Code List

Codes listed

144

searchable definitions

Systems covered

engine, trans, network

Brands

Chevy / GMC / Cadillac / Buick

Tune-related codes

flagged with tuning notes

Read this first: GM engines use a mass airflow sensor together with a MAP sensor, so both the P0101–P0103 MAF family and the P0106–P0108 MAP family are in play after an intake or boost change. GM's cylinder deactivation is AFM and DFM (the P34xx range and P06DD) — not the same system as a HEMI's, and it fails in its own characteristic way.

Search the Code List

Code	System	Definition
P0101	Air & Fuel Metering	Mass Air Flow Sensor Performance The airflow the MAF sensor reports does not agree with what the ECM calculates from throttle position, RPM and manifold pressure. Tuning note: The #1 code after an aftermarket intake or a larger MAF housing. The MAF transfer function has to be rescaled for the new tube diameter — otherwise fueling is wrong everywhere.
P0102	Air & Fuel Metering	Mass Air Flow Sensor Circuit Low Input MAF signal frequency or voltage is below the expected range for current engine conditions. Tuning note: A contaminated or oiled MAF element reads low. Over-oiled reusable filters are the usual cause on LS and LT builds.
P0103	Air & Fuel Metering	Mass Air Flow Sensor Circuit High Input MAF signal is higher than the ECM expects, indicating more air than the engine could physically ingest. Tuning note: On a boosted LS or LT the stock MAF frequency table tops out. Either rescale it or switch the calibration to speed-density (MAF disabled) with a correct VE table.
P0106	Air & Fuel Metering	MAP Sensor Performance Manifold pressure does not correlate with throttle position and engine speed. Tuning note: GM uses MAF and MAP together. On a cammed engine the low, unstable idle vacuum reads as a MAP fault until the idle and VE tables are corrected.
P0107	Air & Fuel Metering	MAP Sensor Circuit Low Voltage MAP signal voltage is below the valid range — usually an open circuit, unplugged sensor or shorted signal wire.
P0108	Air & Fuel Metering	MAP Sensor Circuit High Voltage MAP signal voltage exceeds the valid range for the sensor. Tuning note: A 1-bar sensor pegs out around 15 psi absolute. Boosted builds need a 2-bar or 3-bar sensor and a rescaled MAP transfer function.
P0111	Air & Fuel Metering	Intake Air Temperature Sensor Performance The IAT reading is implausible compared with coolant temperature and ambient conditions. Tuning note: Relocating the IAT into the charge pipe or manifold changes what the ECM sees. Spark and fueling IAT correction tables should be revisited when the sensor moves.
P0112	Air & Fuel Metering	Intake Air Temperature Sensor Circuit Low IAT circuit voltage is low, which the ECM interprets as an impossibly hot intake charge.
P0113	Air & Fuel Metering	Intake Air Temperature Sensor Circuit High IAT circuit voltage is high, typically an open circuit or disconnected sensor.
P0116	Air & Fuel Metering	Engine Coolant Temperature Sensor Performance Coolant temperature readings do not change the way the ECM expects during warm-up or operation.
P0117	Air & Fuel Metering	Engine Coolant Temperature Circuit Low ECT signal voltage low — the ECM sees an impossibly high coolant temperature.
P0118	Air & Fuel Metering	Engine Coolant Temperature Circuit High ECT signal voltage high, usually an open circuit or unplugged sensor.
P0128	Air & Fuel Metering	Coolant Thermostat Below Regulating Temperature The engine did not reach the expected operating temperature within the expected time. Tuning note: Standard after a low-temperature thermostat. The warm-up temperature threshold has to be lowered in the calibration or the code returns every cold start.
P0131	Air & Fuel Metering	O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1) The upstream oxygen sensor on bank 1 reports a persistently lean signal.
P0132	Air & Fuel Metering	O2 Sensor Circuit High Voltage (Bank 1 Sensor 1) The upstream oxygen sensor on bank 1 reports a persistently rich signal.
P0137	Air & Fuel Metering	O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2) The post-catalyst sensor on bank 1 stays low, indicating lean exhaust or a failing sensor.
P0140	Air & Fuel Metering	O2 Sensor Circuit No Activity (Bank 1 Sensor 2) The downstream oxygen sensor signal is not changing at all — an open circuit or a dead sensor. Tuning note: Also appears when rear sensors are removed for headers without disabling the rear O2 monitors in the calibration.
P0171	Air & Fuel Metering	Fuel Trim System Lean (Bank 1) Long-term fuel trim on bank 1 has hit its positive limit — the ECM is adding fuel to correct a lean condition. Tuning note: Injectors, a MAF housing change or a cam swap will do this. Rescale injector flow data and the VE or MAF table rather than letting trims carry the correction.
P0172	Air & Fuel Metering	Fuel Trim System Rich (Bank 1) Long-term fuel trim on bank 1 hit its negative limit — the ECM is pulling fuel out. Tuning note: Larger injectors with the stock injector flow table will do exactly this. Fix the injector data, not the trims.
P0174	Air & Fuel Metering	Fuel Trim System Lean (Bank 2) Long-term fuel trim on bank 2 is at its positive limit. Tuning note: A lean condition on one bank only points at a bank-specific problem — an intake leak, a bad injector, or an exhaust leak ahead of the O2 sensor.
P0175	Air & Fuel Metering	Fuel Trim System Rich (Bank 2) Long-term fuel trim on bank 2 is at its negative limit.
P0176	Air & Fuel Metering	Fuel Composition Sensor Circuit The flex-fuel composition sensor signal is out of range or missing on an E85-capable vehicle. Tuning note: Flex-fuel builds need the ethanol content input working before the calibration can blend fuel and spark between gasoline and E85 tables.
P0182	Air & Fuel Metering	Fuel Temperature Sensor Circuit Low Fuel temperature sensor signal is below the valid range.
P0191	Air & Fuel Metering	Fuel Rail Pressure Sensor Performance Measured fuel rail pressure does not match the commanded value on a direct-injection engine. Tuning note: On LT1, LT4 and L83 direct-injection engines this is the code that shows up when fuel demand outruns the stock high-pressure pump. Pressure has to be logged before adding power.
P0201	Air & Fuel Metering	Injector 1 Control Circuit The ECM detected an electrical fault in the cylinder 1 injector circuit. Tuning note: Injector numbering follows cylinder order, not firing order.
P0202	Air & Fuel Metering	Injector 2 Control Circuit Electrical fault detected in the cylinder 2 injector circuit.
P0203	Air & Fuel Metering	Injector 3 Control Circuit Electrical fault detected in the cylinder 3 injector circuit.
P0204	Air & Fuel Metering	Injector 4 Control Circuit Electrical fault detected in the cylinder 4 injector circuit.
P0205	Air & Fuel Metering	Injector 5 Control Circuit Electrical fault detected in the cylinder 5 injector circuit.
P0206	Air & Fuel Metering	Injector 6 Control Circuit Electrical fault detected in the cylinder 6 injector circuit.
P0207	Air & Fuel Metering	Injector 7 Control Circuit Electrical fault detected in the cylinder 7 injector circuit.
P0208	Air & Fuel Metering	Injector 8 Control Circuit Electrical fault detected in the cylinder 8 injector circuit.
P0230	Air & Fuel Metering	Fuel Pump Relay Control Circuit The ECM detected a fault in the fuel pump relay or its control circuit.
P0300	Misfire & Ignition	Engine Misfire Detected (Random / Multiple Cylinders) The ECM detected misfire that is not isolated to one cylinder, based on crankshaft speed variation. Tuning note: On a big-cam LS or LT the rough idle itself trips the misfire monitor. Confirm with per-cylinder misfire counts in a datalog before chasing parts — but never dismiss misfire under load, which is real and dangerous.
P0301	Misfire & Ignition	Cylinder 1 Misfire Detected Misfire has been detected specifically on cylinder 1.
P0302	Misfire & Ignition	Cylinder 2 Misfire Detected Misfire has been detected specifically on cylinder 2.
P0303	Misfire & Ignition	Cylinder 3 Misfire Detected Misfire has been detected specifically on cylinder 3.
P0304	Misfire & Ignition	Cylinder 4 Misfire Detected Misfire has been detected specifically on cylinder 4.
P0305	Misfire & Ignition	Cylinder 5 Misfire Detected Misfire has been detected specifically on cylinder 5.
P0306	Misfire & Ignition	Cylinder 6 Misfire Detected Misfire has been detected specifically on cylinder 6.
P0307	Misfire & Ignition	Cylinder 7 Misfire Detected Misfire has been detected specifically on cylinder 7.
P0308	Misfire & Ignition	Cylinder 8 Misfire Detected Misfire has been detected specifically on cylinder 8.
P0315	Misfire & Ignition	Crankshaft Position System Variation Not Learned The ECM has not learned the crankshaft position variation values needed to run the misfire monitor accurately. Tuning note: Needs a CASE relearn after a crank sensor, harmonic balancer or ECM change. Skipping it produces phantom misfire codes.
P0316	Misfire & Ignition	Misfire Detected on Startup Misfire occurred in the first few seconds after start-up. Tuning note: Common early warning of a collapsed AFM lifter on a 5.3L or 6.2L. Worth a compression check before it becomes a bent pushrod.
P0324	Misfire & Ignition	Knock Control System Error The knock control system reported an internal fault and knock retard may be unavailable. Tuning note: Never add timing when knock detection is offline. Fix the sensor first — this is one of the few codes that can cost you an engine.
P0325	Misfire & Ignition	Knock Sensor Circuit (Bank 1) Knock sensor circuit fault on bank 1 — the ECM cannot trust its detonation input. Tuning note: Aftermarket headers and loose accessories create noise that reads as knock. Verify with a datalog before assuming the sensor failed.
P0330	Misfire & Ignition	Knock Sensor Circuit (Bank 2) Knock sensor circuit fault on bank 2.
P0351	Misfire & Ignition	Ignition Coil 1 Control Circuit The ECM detected a fault in the cylinder 1 ignition coil primary circuit. Tuning note: Coil numbers follow cylinder order. A tune that adds cylinder pressure will find a weak coil that idled fine before.
P0352	Misfire & Ignition	Ignition Coil 2 Control Circuit Fault detected in the cylinder 2 ignition coil control circuit.
P0353	Misfire & Ignition	Ignition Coil 3 Control Circuit Fault detected in the cylinder 3 ignition coil control circuit.
P0354	Misfire & Ignition	Ignition Coil 4 Control Circuit Fault detected in the cylinder 4 ignition coil control circuit.
P0355	Misfire & Ignition	Ignition Coil 5 Control Circuit Fault detected in the cylinder 5 ignition coil control circuit.
P0356	Misfire & Ignition	Ignition Coil 6 Control Circuit Fault detected in the cylinder 6 ignition coil control circuit.
P0357	Misfire & Ignition	Ignition Coil 7 Control Circuit Fault detected in the cylinder 7 ignition coil control circuit.
P0358	Misfire & Ignition	Ignition Coil 8 Control Circuit Fault detected in the cylinder 8 ignition coil control circuit.
P0008	Camshaft & AFM/DFM	Engine Position System Performance (Bank 1) The crankshaft and camshaft position relationship on bank 1 is outside the allowed window. Tuning note: On LS and LT engines this usually means a stretched or jumped timing chain. Mechanical repair, never a calibration fix.
P0011	Camshaft & AFM/DFM	Camshaft Position Over-Advanced (Bank 1) The bank 1 camshaft is more advanced than commanded, or will not return to the commanded position. Tuning note: On VVT LT engines, a cam actuator that cannot hit target is often oil-related — pressure, viscosity, or a screen full of debris. Cam phaser limiters in the tune must match the hardware.
P0014	Camshaft & AFM/DFM	Camshaft Position Over-Retarded (Bank 1) The bank 1 camshaft is retarded beyond the commanded position.
P0016	Camshaft & AFM/DFM	Crankshaft / Camshaft Position Correlation (Bank 1 Sensor A) The camshaft and crankshaft signals are out of phase beyond the allowed tolerance. Tuning note: Frequently a worn timing chain, a failed cam phaser, or a cam actuator solenoid clogged with debris. Do not tune around this.
P0017	Camshaft & AFM/DFM	Crankshaft / Camshaft Position Correlation (Bank 1 Sensor B) Correlation fault between crankshaft and the bank 1 exhaust camshaft signal.
P0020	Camshaft & AFM/DFM	Camshaft Position Actuator Circuit (Bank 2) Electrical fault in the bank 2 camshaft actuator solenoid circuit.
P0021	Camshaft & AFM/DFM	Camshaft Position Over-Advanced (Bank 2) The bank 2 camshaft is more advanced than commanded.
P0024	Camshaft & AFM/DFM	Camshaft Position Over-Retarded (Bank 2) The bank 2 camshaft is retarded beyond the commanded position.
P0090	Camshaft & AFM/DFM	Fuel Pressure Regulator Control Circuit Electrical fault in the fuel pressure regulator or high-pressure pump control circuit.
P0341	Camshaft & AFM/DFM	Camshaft Position Sensor Performance The camshaft position signal pattern is implausible relative to the crankshaft signal. Tuning note: A non-VVT cam swap on a VVT engine needs the cam sensor and VVT strategy addressed in the calibration or this code is permanent.
P0342	Camshaft & AFM/DFM	Camshaft Position Sensor Circuit Low Camshaft position sensor signal voltage below the valid range.
P0521	Camshaft & AFM/DFM	Engine Oil Pressure Sensor Performance Measured oil pressure does not match what the ECM expects for the current RPM and temperature. Tuning note: Treat as urgent. AFM and DFM engines depend on oil pressure to control the lifters, and low pressure precedes lifter failure.
P0522	Camshaft & AFM/DFM	Engine Oil Pressure Sensor Circuit Low Voltage Oil pressure sensor circuit reads low — either genuinely low pressure or a sensor and wiring fault. Tuning note: Stop the engine and verify with a mechanical gauge before driving. This is not a code to tune out.
P06DD	Camshaft & AFM/DFM	Engine Oil Pressure Control Circuit Stuck Off The two-stage oil pump did not switch to high pressure when commanded. Tuning note: Very common on AFM 5.3L and 6.2L truck engines and often the first sign of an oil pump or pressure control solenoid problem. Address before chasing lifter noise.
P3400	Camshaft & AFM/DFM	Cylinder Deactivation System (Bank 1) Active Fuel Management or Dynamic Fuel Management could not deactivate or reactivate cylinders on bank 1 as commanded. Tuning note: Deleting AFM or DFM mechanically requires the calibration to disable it as well — lifters, oil pump control and torque management. A partial delete leaves the engine confused.
P3425	Camshaft & AFM/DFM	Cylinder 2 Deactivation Solenoid Control Circuit Electrical fault in the cylinder 2 valve-lifter oil manifold solenoid circuit. Tuning note: After an AFM delete the solenoids are gone, so the code is expected until cylinder deactivation is switched off in the calibration.
P3441	Camshaft & AFM/DFM	Cylinder 4 Deactivation Solenoid Control Circuit Electrical fault in the cylinder 4 deactivation solenoid circuit.
P3449	Camshaft & AFM/DFM	Cylinder 5 Deactivation Solenoid Control Circuit Electrical fault in the cylinder 5 deactivation solenoid circuit.
P3465	Camshaft & AFM/DFM	Cylinder 7 Deactivation Solenoid Control Circuit Electrical fault in the cylinder 7 deactivation solenoid circuit.
P0030	Emissions & EVAP	HO2S Heater Control Circuit (Bank 1 Sensor 1) General fault in the bank 1 upstream oxygen sensor heater control circuit.
P0031	Emissions & EVAP	HO2S Heater Control Circuit Low (Bank 1 Sensor 1) The oxygen sensor heater circuit is drawing less current than expected. Tuning note: Header installs with cut or stretched O2 extensions are a frequent cause.
P0135	Emissions & EVAP	O2 Sensor Heater Performance (Bank 1 Sensor 1) The upstream oxygen sensor heater is not bringing the sensor to operating temperature in the expected time.
P0141	Emissions & EVAP	O2 Sensor Heater Performance (Bank 1 Sensor 2) The downstream oxygen sensor heater circuit is not performing to specification.
P0401	Emissions & EVAP	EGR Flow Insufficient The ECM commanded EGR flow and did not see the expected effect.
P0404	Emissions & EVAP	EGR Valve Performance The EGR valve position or flow does not match the commanded value.
P0411	Emissions & EVAP	Secondary Air Injection System Performance The secondary air injection system did not deliver the expected airflow during the cold-start test.
P0420	Emissions & EVAP	Catalyst System Efficiency Below Threshold (Bank 1) The downstream oxygen sensor no longer sees the oxygen-storage behavior a healthy catalyst should produce on bank 1. Tuning note: The most misdiagnosed code there is. An exhaust leak, a lazy rear sensor, or a rich condition produce it without any converter failure. High-flow cats also trip it legitimately.
P0430	Emissions & EVAP	Catalyst System Efficiency Below Threshold (Bank 2) Same catalyst efficiency fault as P0420 but on bank 2.
P0442	Emissions & EVAP	EVAP System Small Leak Detected The evaporative system failed a leak test at the small-leak threshold — often a loose or worn fuel cap.
P0446	Emissions & EVAP	EVAP Vent System Performance The vent valve or its circuit is not behaving as expected during EVAP testing. Tuning note: Spiders and dirt in the vent solenoid are a genuinely common cause on trucks.
P0449	Emissions & EVAP	EVAP Vent Valve Solenoid Control Circuit Electrical fault in the EVAP vent valve solenoid circuit.
P0455	Emissions & EVAP	EVAP System Large Leak Detected A large evaporative leak — a missing fuel cap, a disconnected hose, or a cracked line.
P0496	Emissions & EVAP	EVAP System Flow During Non-Purge Purge flow was detected when the purge valve should have been closed — typically a stuck-open purge solenoid.
P0120	Throttle & ETC	Throttle Position Sensor 1 Circuit The ECM detected a fault in the primary throttle position sensor circuit.
P0121	Throttle & ETC	Throttle Position Sensor 1 Performance Throttle position does not correlate with airflow and manifold pressure. Tuning note: A larger throttle body changes the flow-per-degree relationship. The throttle and airflow tables should be updated to match.
P0122	Throttle & ETC	Throttle Position Sensor 1 Circuit Low Voltage TPS 1 signal voltage below the valid range.
P0123	Throttle & ETC	Throttle Position Sensor 1 Circuit High Voltage TPS 1 signal voltage above the valid range.
P0506	Throttle & ETC	Idle Speed Lower Than Expected Idle speed is below the commanded value. Tuning note: Classic post-camshaft code. The engine needs more idle airflow than the stock tables provide.
P0507	Throttle & ETC	Idle Speed Higher Than Expected Actual idle speed is above the commanded value beyond the allowed tolerance. Tuning note: A big cam, a ported throttle body, or an intake leak. The idle airflow tables need rescaling for the new combination.
P1400	Throttle & ETC	Cold Start Emission Reduction Control System The cold-start emission strategy did not achieve its target — often related to idle speed or spark retard during warm-up. Tuning note: Aggressive cold-start spark or idle changes in a tune will set this. Leave the cold-start strategy closer to stock than you think you need to.
P1516	Throttle & ETC	Throttle Actuator Control Module Throttle Position Performance The throttle body's internal module reports that actual blade position does not match the commanded position. Tuning note: GM-specific. Carbon buildup behind the blade is the usual cause — clean it and relearn before condemning the throttle body.
P2101	Throttle & ETC	Throttle Actuator Position Performance The throttle actuator motor did not move the blade to the commanded position.
P2119	Throttle & ETC	Throttle Actuator Control Throttle Body Range Performance The throttle body could not reach its expected mechanical range during self-test.
P2135	Throttle & ETC	Throttle Position Sensor 1-2 Correlation The two throttle position signals disagree with each other beyond tolerance. Tuning note: Usually a failing throttle body or a corroded connector. The ECM enters reduced power mode until it is fixed.
P0700	Transmission	Transmission Control System (MIL Request) The transmission control module has stored its own fault and is asking the ECM to turn on the check engine light. Tuning note: P0700 is only a pointer. You must read the TCM directly to get the real code — a generic scanner often will not show it.
P0711	Transmission	Transmission Fluid Temperature Sensor Performance Transmission fluid temperature readings are implausible.
P0716	Transmission	Input Speed Sensor Performance The input shaft speed signal does not correlate with engine speed and gear ratio.
P0717	Transmission	Input Speed Sensor Circuit No Signal The TCM is not receiving an input shaft speed signal at all.
P0722	Transmission	Output Speed Sensor Circuit No Signal No output shaft speed signal is reaching the TCM.
P0730	Transmission	Incorrect Gear Ratio The measured ratio between input and output speed does not match any commanded gear. Tuning note: On 6L80 and 8L90 units this points at clutch slip. A torque-management-heavy tune can mask it for a while — that is not a fix, it is a delay.
P0741	Transmission	Torque Converter Clutch System Stuck Off The converter clutch was commanded to lock and slip continued beyond the allowed tolerance. Tuning note: The most common 6L80 and 8L90 complaint. Added torque finds a marginal converter clutch immediately, so TCC apply pressure and torque limits are part of any serious trans calibration.
P0748	Transmission	Pressure Control Solenoid Electrical Electrical fault in a line pressure control solenoid circuit.
P0751	Transmission	Shift Solenoid A Performance Shift solenoid A did not produce the commanded shift.
P0776	Transmission	Pressure Control Solenoid B Performance A pressure control solenoid is not producing the commanded pressure. Tuning note: On 8L90 transmissions this frequently accompanies the shudder complaints and is worth checking before a tune is blamed.
P0842	Transmission	Transmission Fluid Pressure Switch 1 Circuit Low A transmission pressure switch reads low relative to expected line pressure.
P0868	Transmission	Transmission Fluid Pressure Low Measured line pressure is below the commanded value. Tuning note: A worn pump or leaking circuit. Raising pressure in the calibration on top of a mechanical leak will not save the transmission.
P0894	Transmission	Transmission Component Slipping The TCM detected that a clutch or band is slipping beyond acceptable limits. Tuning note: Hard code. Something inside is worn — this is not calibration territory.
P17BF	Transmission	Transmission Adaptive Learning At Limit The TCM's adaptive shift corrections have reached the end of their range. Tuning note: Reset adaptives after a trans calibration change, then let it relearn. Stacking new tables on top of old adaptives makes shift quality worse, not better.
P2714	Transmission	Pressure Control Solenoid D Performance Pressure control solenoid D is not delivering commanded pressure.
P2723	Transmission	Pressure Control Solenoid E Stuck Off Pressure control solenoid E did not respond to its command.
P0033	Boost & Forced Induction	Turbocharger Bypass Valve Control Circuit Fault in the turbocharger bypass or recirculation valve control circuit.
P0234	Boost & Forced Induction	Turbocharger / Supercharger Overboost Measured boost exceeded the maximum the calibration allows. Tuning note: Adding a pulley, a smaller supercharger pulley or a turbo upgrade without raising the overboost limit sets this immediately and often triggers a power cut.
P0243	Boost & Forced Induction	Turbocharger Wastegate Solenoid Circuit General electrical fault in the wastegate control solenoid circuit.
P0245	Boost & Forced Induction	Turbocharger Wastegate Solenoid Low Wastegate control solenoid circuit voltage is below the valid range.
P0299	Boost & Forced Induction	Turbocharger / Supercharger Underboost Boost pressure is below the commanded target. Tuning note: On boosted GM applications check for charge-pipe leaks and wastegate control before touching the calibration.
P2263	Boost & Forced Induction	Turbocharger Boost System Performance The boost system as a whole is not producing the pressure the ECM expects.
P0601	Communication & Module	Control Module Read Only Memory Error The ECM's internal memory checksum failed. Tuning note: An interrupted write can cause this. Do not attempt a flash on a weak battery — use a maintainer.
P0602	Communication & Module	Control Module Not Programmed The module is missing required calibration data. Tuning note: Normal on a replacement module before programming, and on a flash that did not complete.
P0603	Communication & Module	Control Module Long Term Memory Reset Keep-alive memory was cleared — commonly after a battery disconnect or an internal fault.
P0606	Communication & Module	Control Module Internal Performance The ECM's internal processor self-test failed.
P1682	Communication & Module	Ignition 1 Switch Circuit 2 The ECM sees a disagreement between the two ignition voltage inputs. Tuning note: GM-specific and usually a wiring, ignition switch or ground problem rather than a module failure.
U0073	Communication & Module	Control Module Communication Bus A Off The high-speed communication bus has shut down, usually because a module or wiring fault is corrupting it.
U0100	Communication & Module	Lost Communication With ECM/PCM Another module can no longer talk to the engine control module. Tuning note: Shows up during interrupted flashes. Recover the module rather than pulling the battery and hoping.
U0101	Communication & Module	Lost Communication With TCM The transmission control module has stopped responding on the bus.
U0121	Communication & Module	Lost Communication With ABS Module The anti-lock brake module is not communicating.
U0140	Communication & Module	Lost Communication With Body Control Module The BCM is not responding to network requests.
C0561	Sensors & Electrical	System Disabled Information Stored A chassis module has disabled a function such as traction control and stored the reason.
P0068	Sensors & Electrical	Throttle Body Airflow Performance Manifold pressure, throttle position and airflow do not agree with each other. Tuning note: Often an intake leak downstream of the MAF, or a MAF that has not been rescaled after an intake change.
P0335	Sensors & Electrical	Crankshaft Position Sensor Circuit The crankshaft position signal is missing or erratic. Tuning note: An erratic crank signal causes stalling and phantom misfire codes. Check the connector and the reluctor wheel.
P0336	Sensors & Electrical	Crankshaft Position Sensor Performance The crankshaft signal is present but its pattern is implausible.
P0500	Sensors & Electrical	Vehicle Speed Sensor No usable vehicle speed signal is reaching the ECM. Tuning note: Tire size and gear ratio changes must be entered in the calibration — otherwise speed, shift points and the speedometer are all wrong.
P0562	Sensors & Electrical	System Voltage Low Battery or charging system voltage is below the ECM's minimum threshold. Tuning note: Fix charging problems before flashing anything. Low voltage during a write is how modules get corrupted.
P0563	Sensors & Electrical	System Voltage High System voltage is above the expected range, typically an overcharging alternator.
P0641	Sensors & Electrical	5-Volt Reference 1 Circuit The ECM's 5-volt sensor reference circuit is out of range, which affects every sensor sharing it. Tuning note: One shorted sensor can drag the reference down and set a fistful of unrelated codes. Fix this first.
P0651	Sensors & Electrical	5-Volt Reference 2 Circuit The second 5-volt reference circuit is out of range.
P0685	Sensors & Electrical	ECM Power Relay Control Circuit Open Fault in the circuit controlling the main ECM power relay.
P0691	Sensors & Electrical	Cooling Fan 1 Control Circuit Low The cooling fan control circuit reads low — relay, wiring or fan motor. Tuning note: Fan-on temperatures are commonly lowered in a performance calibration. Verify the fans actually respond afterward.
P0715	Sensors & Electrical	Input / Turbine Speed Sensor Circuit The input or turbine speed sensor circuit is not delivering a valid signal.
P2610	Sensors & Electrical	ECM Engine Off Timer Performance The ECM's internal soak timer is not tracking correctly, which affects cold-start and readiness monitors.

How to Read the Code Numbers

The first character tells you which system stored the fault. P is powertrain, U is network or communication, B is body, and C is chassis.

The second character tells you who defined it. P0xxx codes are generic and mean the same thing on every OBD-II vehicle sold since 1996. P1xxx codes are manufacturer specific. The P2xxx and P3xxx ranges are a mix of both, and newer modules also use hexadecimal codes such as P06DD and P000A.

The remaining digits identify the specific circuit, cylinder, or monitor. Injector codes P0201 through P0208 and coil codes P0351 through P0358 both follow cylinder order, not firing order — a detail that sends plenty of people chasing the wrong coil.

One more thing worth knowing: a stored code is a symptom report, not a diagnosis. P0420 does not mean “replace the catalytic converter.” It means the downstream oxygen sensor no longer sees the difference it expects to see. An exhaust leak, a lazy sensor, or a fueling problem produce the same code.

Codes We See After a Tune

Some codes are hardware failures. Others are the module correctly reporting that the engine no longer matches the calibration it was given. The second group is fixable in software, and it is the group we deal with every day:

P0101 — an intake or a larger MAF housing with the stock transfer function. P0128 — a low-temperature thermostat the warm-up thresholds were never adjusted for. P0108 — a 1-bar MAP sensor pegged out on a boosted build. P0234 — a smaller blower pulley against the factory overboost limit. P0506 or P0507 — a camshaft the idle airflow tables know nothing about. P3400 and the P34xx solenoid codes — an AFM or DFM delete done in hardware but not in the calibration.

Codes that must never be tuned around: P0016 and P0017 crank-to-cam correlation, P0521 / P0522 / P06DD oil pressure, P0324, P0325 and P0330 knock control faults, and P0894 transmission slip. P0316 misfire on startup on a 5.3L or 6.2L is often the first sign of a collapsing AFM lifter — worth a compression check before it becomes a bent pushrod and a top-end teardown.

Got a GM Code You Cannot Solve?

Send us the code and a datalog. We read MAF, MAP, knock, fuel trim and misfire data on every remote tune submission and we will tell you straight whether it is a calibration fix or a hardware problem.

Talk to a Tuner

Frequently Asked Questions

How do I read DTC codes on a Chevy, GMC or Cadillac?

Any generic OBD-II scanner will read stored P-codes from the port under the dash. Transmission codes behind P0700, and GM's own P1xxx codes, need a capable scan tool or tuning software such as HP Tuners — a basic reader will show you P0700 and nothing useful behind it.

Do I need to unlock my GM ECM before tuning?

No. Unlike 2015 and newer Dodge, Jeep, RAM and Chrysler vehicles, GM engine control modules are not locked — they flash straight through the OBD-II port. The exception is the 2017 and newer 8-speed and 10-speed T87A transmission module, which does need an unlock service before it can be written.

What is the difference between AFM and DFM?

Active Fuel Management deactivates a fixed set of four cylinders on V8s. Dynamic Fuel Management, on later engines, can run 17 different cylinder patterns. Both rely on oil-pressure-controlled lifters, which is why oil pressure codes like P06DD and lifter failures show up together so often.

Will a custom tune clear my check engine light?

Only if the code came from a calibration limit rather than a mechanical fault. Rescaling a MAF curve, adjusting warm-up thresholds, correcting idle airflow for a camshaft, or properly disabling AFM after a hardware delete are real fixes. A collapsed lifter, a stretched chain or a slipping clutch pack are not.

Can a tune delete AFM or DFM?

The calibration side can be switched off, and it must be if the hardware has been deleted — lifters, oil pump control and torque management all have to agree. Software alone does not remove the hardware, and hardware alone leaves the ECM commanding a system that is no longer there.

Can I keep driving with the check engine light on?

Depends entirely on the code. A small EVAP leak is not urgent. Low oil pressure, crank-to-cam correlation, or misfire under load can destroy an engine. If the light is flashing, stop driving — a flashing MIL means active misfire dumping raw fuel into the converters.

More Tuning Tips

GM ECM & T87A TCM Unlock / Programming · GM, Chevy, GMC & Cadillac Remote Tuning · MAP Sensor kPa to Boost Conversion Chart · HP Tuners Credit System Explained

Tuning a different platform? See our Dodge, Jeep, RAM & Chrysler DTC code list.

This list is a reference for diagnosis, not a repair manual. Definitions describe what the module detected — always confirm with a proper diagnosis before replacing parts. Coverage focuses on 2005 and newer Chevrolet, GMC, Cadillac and Buick gasoline platforms, including LS, LT and Ecotec engines.