GMC OBD/OBD2 Codes >> G-Series – Sierra – Suburban – Yukon (1994 – 1995)

ModelYearEngine identificationSystem
G-Series 6.5L1994-95VIN  position 8 = P/YGM
Sierra C/K Pickup 6.5L1994-95VIN  position 8 = F/P/SGM
Suburban 6.5L1994-95VIN  position 8 =  FGM
Yukon  6.5L1994-95VIN  position 8 =  SGM

General information

  • Malfunction indicator lamp (MIL) will illuminate if certain faults are recorded .
  • ECM operates in backup mode if sensors fail, to enable vehicle to be driven to repair shop.
  • Trouble codes can be displayed by the MIL or by using a Scan Tool connected to the data link connector (DLC).


  • Access data link connector (DLC).
  • Jump data link connector (DLC) terminals A and B [1].
  • Switch ignition ON. 00 NOT start engine.
  • Count MIL flashes. Note trouble codes. Compare with trouble code table.
  • Firstly trouble code 12 will be displayed 3 times.
  • Trouble codes consist of 2 groups, displayed as follows:
o First group indicates the ‘tens’ of the trouble code [2] [A].
o Second group indicates the ‘units’ of the trouble code [2] [C].
o A short pause separates each group [2] [B].
o A long pause separates each trouble code [2] [D].
o For example: Trouble code 12 displayed [2]. Start of diagnosis.
• Each additional trouble code will now be displayed 3 times, in ascending order.
NOTE: If no additional trouble codes are stored, code 12 will continue to be displayed.
• Trouble codes can also be displayed by using a Scan Tool connected to the data link connector (DLC) [1].


NOTE: Disconnecting battery ground lead may cause driveability problems until the engine management system relearns basic values.
  • Ensure ignition switched OFF.
  • Disconnect battery ground cable for 30 seconds.
  • Reconnect battery ground cable.
  • Repeat checking procedure to ensure no trouble codes remain in ECM fault memory.
NOTE: Disconnecting battery ground lead may also erase memory from electronic units, such as radio.
  • Trouble codes can also be erased by using a Scan Tool connected to the data link connector (DLC).

Trouble code  identification

Flash codeFault locationProbable cause
12Start of diagnosisNo engine speed (RPM) signal received
13Fuel shut-off solenoid -circuit malfunctionWiring open circuit, fuel shut-oft solenoid, ECM
14Engine coolant temperature (EeT) sensor voltage lowWiring, ECT sensor, ECM
15Engine coolant temperature (EeT) sensor voltage highWiring open circuit, ECT sensor, ECM
16Vehicle speed sensor (VSS) -no/low signalWiring, VSS, ECM
17Injection pump position sensor, high resolution -circuit malfunctionWiring, injection pump position sensor, ECM
18Injection pump position sensor, low resolution -circuit malfunctionWiring, injection pump position sensor, ECM
19Crankshaft position (CKP) sensor -circuitmalfunctionWiring, CKP sensor, ECM
21Accelerator pedal position (APP) sensor 1voltage highWiring, APP sensor, ECM
22Accelerator pedal position (APP) sensor 1voltage lowWiring, APP sensor, ECM
23Accelerator pedal position (APP) sensor 1 to 2/3 -signal variationWiring, APP sensor, ECM
24Vehicle speed sensor (VSS) no signalWiring, VSS, ECM
25Accelerator pedal position (APP) sensor 2voltage highWiring, APP sensor, ECM
26Accelerator pedal position (APP) sensor 2voltage lowWiring, APP sensor, ECM
27Accelerator pedal position (APP) sensor 2 to 1/3signal variationWiring, APP sensor, ECM
28Transmission gear pressure switch, signal -circuit malfunctionWiring open circuit/short circuit to ground,reverse/D1/D2/D3/D4 gear pressure switch(es), ECM
29Glow plug relay -circuit malfunctionWiring, glow plug relay, ECM
31Exhaust gas recirculation (EGR) vacuum/ barometric pressure (BARO) sensor -voltage lowWiring, EGR vacuum/BARO sensor, ECM
32Exhaust gas recirculation (EGR) system -malfunctionWiring, vacuum pipes, EGR vacuum sensor, EGR valve
33Exhaust gas recirculation (EGR) vacuum/ barometric pressure (BARO) sensor -voltage highWiring, EGR vacuum/BARO sensor, ECM
34Fuel injection timing. command/actual -signalvariationWiring, fuel injection timing actuator, ECM
35Fuel injection duration -pulse width signal shorter than expectedWiring, fuel injection duration control solenoid, fuel injection pump control module, ECM
36Fuel injection duration -pulse width signal longer than expectedWiring, fuel injection duration control solenoid, fuel injection pump control module, ECM
37Brake pedal position (BPP) switch -stuck ONWiring, BPP switch, ECM
38Brake pedal position (BPP) switch -stuck OFFWiring, BPP switch, ECM
39Brake pedal position (BPP) switch -stuck OFFWiring, BPP switch, ECM
41Brake pedal position (BPP) switch. torque converter clutch (TCC) -circuit malfunctionWiring, BPP switch, ECM
42Fuel temperature sensor -voltage lowWiring, fuel temperature sensor, ECM
43Fuel temperature sensor -voltage highWiring, fuel temperature sensor, ECM
44Exhaust gas recirculation (EGR) valve -circuit malfunctionWiring, fuses, EGR valve
45Exhaust gas recirculation (EGR) vent valve circuit malfunctionWiring, fuses, EGR vent valve
46Malfunction indicator lamp (MIL) -circuitmalfunctionWiring, fuses, MIL
47Intake air temperature (IAT) sensor -voltage lowWiring short circuit to ground, IAT sensor, ECM
48Intake air temperature (IAT) sensor -voltage highWiring, IAT sensor, ECM
49Service throttle soon warning lamp -circuitmalfunctionWiring, fuses, service throttle soon warning lamp
51Engine control module (ECM). PROM malfunctionPoor connections, incorrect programming, ECM
52System voltage highAlternator, jump started
53System voltage highAlternator, jump started
54Engine control module (ECM) malfunctionCheck trouble code 17, if not: replace ECM
56Fuel injection pump calibration resistor circuit malfunctionWiring, calibration resistor
57Engine control module (ECM), sensor supply voltage -circuit malfunctionWiring short to ground, poor connections, MAP sensor
58Transmission fluid temperature (TFT) sensorvoltage lowWiring short circuit to ground, TFT sensor, ECM
59Transmission fluid temperature (TFT) sensor voltage highWiring open circuit, TFT sensor, ECM
61Turbocharger (TC) boost pressure sensor voltage highWiring, TC boost pressure sensor, ECM
62Turbocharger (TC) boost pressure sensor voltage lowWiring short circuit to ground, TC boost pressure sensol”, ECM
63Accelerator pedal position (APP) sensor 3 voltage highWiring, APP sensor, ECM
64Accelerator pedal position (APP) sensor 3 voltage lowWiring, APP sensor, ECM
65Accelerator pedal position (APP) sensor 3 to 1/2signal variationWiring, APP sensor, ECM
66Transmission 3rd-2nd control solenoid -circuit malfunctionWiring, control solenoid, ECM
67Torque converter clutch (TCC) solenoid -circuit malfunctionWiring, TCC solenoid, ECM
69Torque converter clutch (TCC) solenoid -stuck ONWiring open circuit/short circuit to ground, transmission internal wiring, TCC solenoid, transmission mechanical fault, ECM
71Cruise control , set/coast switch -circuit malfunctionWiring, poor connections, set/coast switch
72Vehicle speed sensor (VSS) -loss of signalWiring, V55, ECM
73Transmission fluid pressure (TFP) control solenoid -circuit malfunctionWiring, poor connection, TFP solenoid
74Transmission input shaft speed sensor-circuit malfunctionWiring, input shaft speed sensor, ECM
75System voltage low, engine control module (ECM)Wiring, battery, alternator, ECM
76Cruise control, resume/acceleration switch -circuit malfunctionWiring, poor connections, resumel acceleration switch
78Turbocharger (TC) wastegate regulating valve -circuit malfunctionWiring, TC wastegate regulating valve, ECM
79Transmission fluid temperature (TFT) highTransmission mechanical fault, towing weight limit exceeded
81Transmission shift solenoid (SS), 2nd-3rd -circuit malfunctionWiring, 55, ECM
82Transmission shift solenoid (SS), 1st-2nd circuit malfunction .Wiring, SS, ECM
83Torque converter clutch (TCC) solenoid, pulse width modulated -circuit malfunctionWiring, TCC solenoid, ECM
84Accelerator pedal position (APP) sensor 1/2/3intermittent circuit malfunctionWiring, poor connections, APP sensor
85Transmission inpuUoutput shaft speed, ratio variation -out of rangeWiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
86Transmission inpuUoutput shaft speed, ratiovariation -lower than expectedWiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
87Transmission inpuUoutput shaft speed, ratio variation -higher than expectedWiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
88Fuel injection pump timing -out of rangeFuel injection pump timing incorrectly set
91Power balance, cylinder 1Check other trouble codes, if not: mechanical fault
92Power balance, cylinder 2Check other trouble codes, if not: mechanical fault
93Power balance, cylinder 3Check other trouble codes, if not: mechanical fault
94Power balance, cylinder 4Check other trouble codes, if not: mechanical fault
95Power balance, cylinder 5Check other trouble codes, if not: mechanical fault
96Power balance, cylinder 6Check other trouble codes, if not: mechanical fault
97Power balance, cylinder 7Check other trouble codes, if not: mechanical fault
98Power balance, cylinder 8Check other trouble codes, if not: mechanical fault
99Accelerator pedal position (APP) sensor 2 supply voltage lowWiring, poor connections, APP sensor