GM OBD I Codes
12 = ERROR CODE DIAGNOSTIC SYSTEM FUNCTIONING CORRECTLY
13 = OXYGEN SENSOR CIRCUIT OPEN
14 = COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT (HIGH TEMP)
15 = COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT (LOW TEMP)
21 = THROTTLE POSITION SENSOR (TPS) CIRCUIT (HIGH)
22 = THROTTLE POSITION SENSOR (TPS) CIRCUIT (LOW)
23 = MANIFOLD AIR TEMP (MAT) or INTAKE AIR TEMP (IAT) CIRCUIT (LOW TEMP)
24 = VEHICLE SPEED SENSOR (VSS) CIRCUIT
25 = MANIFOLD AIR TEMP (MAT) or INTAKE AIR TEMP (IAT) CIRCUIT (HIGH TEMP)
26 = QUAD-DRIVER (QDM) ERROR (if applicable)
32 = EXHAUST GAS RECIRCULATION (EGR) CIRCUIT
33 = MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (VOLTAGE HIGH-LOW VACUUM)
34 = MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (VOLTAGE LOW-HIGH VACUUM)
35 = IDLE SPEED CONTROL (ISC) CIRCUIT
41 = CYLINDER SELECT ERROR (FAULTY OR INCORRECT MEM-CAL)
42 = ELECTRONIC SPARK TIMING (EST) CIRCUIT
43 = ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
44 = OXYGEN SENSOR CIRCUIT (LEAN EXHAUST)
45 = OXYGEN SENSOR CIRCUIT (RICH EXHAUST)
51 = MEM-CAL ERROR (FAULTY OR INCORRECT MEM-CAL)
53 = SYSTEM OVER VOLTAGE
54 = FUEL PUMP CIRCUIT (LOW VOLTAGE)
55 = ECM ERROR
61 = DEGRADED OXYGEN SENSOR
66 = A/C PRESSURE SENSOR CIRCUIT