GM OBD Codes
decoded & explained
The codes Chevy, GMC and Cadillac owners actually see — MAF self-test, thermostat, idle and catalysts — with clear causes and fixes.
GM (Chevrolet, GMC, Cadillac) check engine light codes
General Motors uses standard OBD-II engine codes, plus a well-known set of manufacturer-specific codes. GM’s MDI/Tech2 tools add depth, but engine codes read on any scanner.
Here are the codes most reported on Silverado, Equinox, Tahoe, Camaro and Cadillac models.
OBD-II code decoder
—
—
—
Most common GM (Chevrolet, GMC, Cadillac)
Classic GM faults behind these codes.
| Code | Description |
|---|---|
| P0011 | "A" Camshaft Position Timing Over-Advanced (Bank 1) |
| P0128 | Coolant Thermostat Below Regulating Temperature |
| P0171 | System Too Lean (Bank 1) |
| P0300 | Random/Multiple Cylinder Misfire |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) |
| P0446 | EVAP Vent Control Circuit Malfunction |
| P0507 | Idle Control System RPM Higher Than Expected |
| P1101 | MAF Sensor Out of Self-Test Range |
Common GM (Chevrolet, GMC, Cadillac) faults
Classic GM faults behind these codes.
MAF self-test (P1101) — a dirty or failing MAF sensor, very common across GM models.
Thermostat (P0128) — stuck-open thermostat, a classic GM fault.
High idle (P0507) — vacuum leaks or throttle carbon on many models.
EVAP vent (P0446) — vent valve or charcoal canister faults.
VVT timing (P0011) — oil pressure or solenoid issues on VVT engines.
GM (Chevrolet, GMC, Cadillac) FAQ
What does P1101 mean on a Chevy?
Why does my GM show P0128?
What causes P0507 on GM models?
Are GM codes the same across brands?
Can I fix a GM code with a cheap scanner?
Codes vary slightly by model, year and engine. Always confirm with a proper diagnosis. Manufacturer-specific codes (P1xxx/P2xxx) may differ from generic descriptions.
Continue reading
Stop Coding Alone: OPC-Skills Gives Your AI Agent Superpowers
OpenClaw: Build Your Personal AI Assistant in Minutes
Top 20 AI Tools Every Developer Should Know in 2026
GibsonAI/memori: Structured Memory Infrastructure for Production AI Agents
Decode your GM (Chevrolet, GMC, Cadillac) code now
Use the free decoder below, or browse the most common GM (Chevrolet, GMC, Cadillac) codes.