GM Jimmy, Rally, Sierra C/K Pickup, Sonoma, Suburban, Vandura, Yukon OBD1 Codes

GM

Various Models
Trouble Code	Fault Location	Probable Cause
12	Start of diagnosis	No engine speed (RPM) signal received
13	Oxygen sensor (02S)/heated oxygen sensor (H02S)	Wiring open circuit, 02S/H02S, ECM
14	Engine coolant temperature (ECT) sensor -voltage high/low	Wiring, ECT sensor, ECM
15	Engine coolant temperature (ECT) sensor -voltage high	Wiring open circuit, ECT sensor, ECM
16	Vehicle speed sensor (VSS) -no signal	Wiring, VSS, ECM
21	Throttle position (TP) sensor -voltage high/ low	Wiring, TP sensor, ECM
22	Throttle position (TP) sensor -voltage low	Wiring open circuit/short circuit to ground, TP sensor, ECM
23	Intake air temperature (IAT) sensor -voltage high	Wiring, IAT sensor, ECM
24	Vehicle speed sensor (VSS) -no signal	Wiring, VSS, ECM
25	Intake air temperature (IAT) sensor -voltage low	Wiring short circuit to ground, IAT sensor, ECM
26	Engine control module (ECM), quad driver/ output driver -circuit malfunction	Wiring, ECM controlled components, ECM * (see below for additional information)
27	Engine control module (ECM), quad driver/ output driver -circuit malfunction	Wiring, ECM controlled components, ECM * (see below for additional information)
28	Transmission gear pressure switch, signal -circuit malfunction	Wiring open circuit/short circuit to ground, reverse/D1/D2/D3/D4 gear pressure switch(es), ECM
31	Throttle control system -malfunction	Wiring, throttle control motor, throttle control module, ECM
32	Exhaust gas recirculation (EGR) solenoid	Wiring, poor connections, EGR valve, ECM
33	Manifold absolute pressure (MAP) sensor -voltage high	Wiring, hose blocked/leaking, MAP sensor, ECM
34	Manifold absolute pressure (MAP) sensor -voltage low	Wiring open circuit/short circuit to ground, MAP sensor, ECM
35	Idle air control (lAC) valve	Wiring, lAC valve, intake system leaking, fuel system, PCV valve, mechanical fault, ECM
36	Auxiliary idle air control valve	Wiring, idle air control valve, vacuum pipes, ECM
37	Brake pedal position (BPP) switch for torque converter clutch (TCC) -stuck ON	Wiring, BPP switch, ECM
38 (1994-1995)	Brake pedal position (BPP) switch, torque converter clutch (TCC) -stuck OFF	Wiring, BPP switch, ECM
38 (1992-1993)	Knock sensor (KS) -circuit malfunction	Wiring open circuit, KS, ECM
39 (1992-1993)	Knock sensor (KS) -circuit malfunction	Wiring short circuit, KS, ECM
39 (Automatic transmission 4L80E 1994)	Brake pedal position (BPP) switch -stuck OFF	Wiring, BPP switch, ECM
41	Crankshaft position (CKP) sensor, 1X reference signal -circuit malfunction	Wiring, ICM, ECM
42	Ignition control, bypass/timing signal -circuit malfunction	Wiring, poor connections, ICM, ECM
43	Knock sensor (KS)/knock control module -circuit malfunction	Wiring, KS, knock control module, ECM
44	Oxygen sensor (02S)/heated oxygen sensor (H02S) -mixture lean	Wiring open circuit/short circuit to ground injector(s) blocked, fuel contamination, pressure low, exhaust system leaking, 02S/ H02S, ECM
45	Oxygen sensor (02S)/heated oxygen sensor (H02S) -mixture rich	Wiring open circuit, fuel pressure high, injector(s) leaking, 02S/H02S, EVAP purge valve, TP sensor, EGR system, ECM
51	Engine control module (ECM), PROM malfunction	Poor connections, incorrect programming : ECM
52 (1992-1993)	Engine control module (ECM) -malfunction	ECM, poor connections
52 (1994-1995)	System voltage -high	Alternator, jump started
53	System voltage -high	Alternator, jump started
54	Fuel pump circuit -voltage low	Wiring open circuit/short circuit to ground fuel pump relay, engine oil pressure warning lamp/fuel pump switch
55	Engine control module (ECM) -malfunction	ECM
58	Transmission fluid temperature (TFT) sensor -voltage low	Wiring short circuit to ground, TFT sensor, ECM
59	Transmission fluid temperature (TFT) sensor -voltage high	Wiring open circuit, TFT sensor, ECM
66	Transmission 3rd-2nd control solenoid circuit malfunction	Wiring, control solenoid, ECM
67	Torque converter clutch (TCC) solenoid circuit malfunction	Wiring, TCC solenoid, ECM
68	Torque converter clutch (TCC) -slipping	Wiring, TCC solenoid, transmission mechanical fault, ECM
69	Torque converter clutch (TCC) solenoid stuck ON	Wiring open circuit/short circuit to ground transmission internal wiring, TCC solenoid transmission mechanical fault, ECM
72	Vehicle speed sensor (VSS) -loss of signal	Wiring, VSS, ECM
73	Transmission fluid pressure (TFP) control solenoid -circuit malfunction	Wiring, poor connection, TFP solenoid
74	Transmission input shaft speed sensor circuit malfunction	Wiring, input shaft speed sensor, ECM
75	System voltage, engine control module (ECM) -low	Wiring, battery, alternator, ECM
79	Transmission fluid temperature (TFT) -high	Transmission mechanical fault, tOWing weight limit exceeded
81	Transmission shift solenoid (SS), 2nd-3rd circuit malfunction	Wiring, SS, ECM
82	Transmission shift solenoid (SS), 1st-2nd circuit malfunction	Wiring, SS, ECM
83	Torque converter clutch (TCC) solenoid, pulse width modulated -circuit malfunction	Wiring, TCC solenoid, ECM
85	Transmission input/output shaft speed, ratio variation -out of range	Wiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
86	Transmission input/output shaft speed, ratio variation -lower than expected	Wiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
87	Transmission input/output shaft speed, ratio variation -higher than expected	Wiring, input shaft speed sensor, output shaft speed sensor, mechanical fault

*Depending on model, year and equipment level, the following components may be connected to this circuit. Use of the vehicle wiring diagram is recommended to confirm which components are fitted. – A/C compressor clutch relay – A/C condenser blower motor relay – Engine coolant blower motor relay – Engine coolant ‘hot’ warning lamp – Evaporative emission (EVAP) canister purge valve – Exhaust gas recirculation (EGR) solenoid – Malfunction Indicator Lamp (MIL) – Torque converter clutch (TCC) solenoid – Transmission shift solenoids (SS) – Transmission shift warning lamp (MT)