Chevrolet & GMC fault codes
Chevrolet and GM vehicles are volume sellers with a known set of aging-fleet fault patterns: cracked intake manifold gaskets on the older V6/V8s, EVAP purge and vent valves that stick or ingest debris, and exhaust manifold bolt breakage on Silverado and Tahoe trucks that can trigger catalyst-efficiency codes. Most are straightforward, DIY-friendly fixes once you know where these platforms typically fail.
Chevrolet-specific diagnostic tips
- On older 3.1/3.4/3.8 V6s and some V8s, cracked intake manifold gaskets cause lean codes and coolant loss. Use the updated GM gasket and proper torque sequence.
- EVAP codes on GM trucks and SUVs commonly trace to a sticky purge solenoid or a vent valve that has ingested dust and debris. Check both before dropping the tank.
- Exhaust manifold bolt breakage on the 4.8/5.3/6.0 LS V8s (Silverado, Tahoe, Suburban) causes an exhaust leak that can trigger P0420. Listen for a tick on cold startup and inspect for broken bolts.
- Use ACDelco or Delphi sensors and ignition parts where possible. GM engines run best on their factory-spec components.
In-depth Chevrolet code guides
Hand-researched, Chevrolet-specific diagnosis, costs and fixes.
Common codes on Chevrolet & GMC
Generic OBD-II codes our guides flag as common on Chevrolet vehicles.
Left Front Wheel Speed Sensor Circuit
Intake Camshaft Timing Over-Advanced (Bank 1)
Exhaust Camshaft Timing Over-Advanced (Bank 1)
Crankshaft/Camshaft Position Correlation (Bank 1, Sensor A)
Crankshaft/Camshaft Position Correlation (Bank 1, Sensor B)
Mass Air Flow (MAF) Sensor Range/Performance Problem
Mass Air Flow (MAF) Sensor Circuit Low Input
Intake Air Temperature (IAT) Sensor Circuit High
Engine Coolant Temperature (ECT) Sensor Circuit High
Insufficient Coolant Temperature for Closed Loop
Coolant Thermostat Below Regulating Temperature
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
System Too Lean (Bank 1)
System Too Rich (Bank 1)
System Too Lean (Bank 2)
System Too Rich (Bank 2)
Throttle/Pedal Position Sensor B Circuit High
Random/Multiple Cylinder Misfire Detected
Knock Sensor 1 Circuit Low (Bank 1)
Crankshaft Position Sensor Circuit Malfunction
Camshaft Position Sensor Circuit Malfunction
Exhaust Gas Recirculation (EGR) Flow Insufficient
EVAP System Malfunction
EVAP System Small Leak Detected
EVAP Vent Control Circuit Malfunction
EVAP System Large Leak Detected
EVAP System Very Small Leak Detected
EVAP Leak Detected (Loose/Faulty Fuel Cap)
Idle Air Control (IAC) System Malfunction
Idle Air Control System RPM Lower Than Expected
Idle Air Control System RPM Higher Than Expected
Engine Oil Pressure Sensor Range/Performance
System Voltage High
ECM/PCM Processor Fault
Transmission Control System Malfunction
Torque Converter Clutch Circuit Malfunction
Torque Converter Clutch Performance / Stuck Off
O2 Sensor Signal Stuck Lean (Bank 1, Sensor 1)
Lost Communication With ECM/PCM A
Lost Communication With TCM