1992 - 1995 6.5L GM Diesel DTC Retrieval

6.5L Diesel OBD-I Code Reading Procedures

1992 to 1995 Chevrolet and GMC trucks equipped with the 6.5L turbocharged diesel feature a first generation on-board diagnostic (OBD-I) system. The system is much simpler and largely less functional than the later OBD-II system, however it serves its purpose as an engine troubleshooting tool. Retrieving codes from the OBD-I system can be performed with select code readers, but it can also be done with no special equipment. Engine DTCs (diagnostic trouble codes) can be read by simply initiating the diagnostic sequence and reading any stored codes by monitoring the "Service Engine Soon" light located to the left of the tachometer in the gauge cluster. The following procedures are not compatible with later OBD-II systems - verify that your truck is equipped with an OBD-I system before attempting these procedures.

OBD-I connector location

The OBD I connector is located beneath the dash and just left of the steering column. For reference, it is almost directly above the clutch pedal on trucks equipped with a manual transmission (click image at left to view fullsize). As previously mentioned, these procedures are applicable to pre-1996 model year trucks equipped with the 6.5L GM/Detroit diesel. 1996 and later model year trucks will feature an OBD II system, which is completely different and more sophisticated than the earlier diagnostics feature. There are several code readers that will read the DTCs stored in an OBD I system, however they can also be read without the need for special equipment. Refer to the connector pinout diagram and procedures below in order to read any stored DTCs from your 1992 through 1995 6.5L diesel.

12 pin OBD-I connector pinout diagram

Pinout diagram for 12 pin GM OBD-I connector

1) With the ignition switch in the "OFF" position, jump (connect) the "A" and "B" terminals - a small length of 14-16 AWG solid core wire stripped at both ends seems to work well, but there are obviously many methods for accomplishing this.

2) Switch the ignition switch to the "RUN" position, which will initiate the glow plug preheat sequence.

3) Monitor the "Service Engine Soon" light, which will indicate any and all stored DTCs. DTCs are displayed in a manner reminiscent of Morse Code, using the SES light as an indicator and a combination of long and short pauses between illuminations. To read a DTC, count the number of times the SES light flashes with only short pauses between each flash, then repeat after the following long pause. A long pause will always indicate that the sequence has moved on to the second number or to the next DTC. To avoid confusion, there are NO codes that have a zero in the number. For example:

(let "-" denote the length of the pause between SES light flashes)

SES-----SES-SES would indicate a DTC 12

SES-SES-----SES-SES-SES would indicate a DTC 23

SES-SES-SES-----SES-SES-SES-SES-SES would indicate a DTC 35

And so forth. All DTCs will appear in numerical order and repeat themselves three times before cycling to the next stored DTC. The DTC 12, which is simply a check code meaning that the diagnostic system is functioning, will be displayed three times before any stored DTCs are displayed. In other words, when starting the diagnostic sequence, DTC 12 will be displayed three times before moving on to the next code. If there are no stored DTCs, DTC 12 will continue to display perpetually.

4) All stored DTCs can be cleared by simultaneously depressing the accelerator and brake pedals while the code reading sequence is taking place (i.e. A & B terminals jumped, key in the "RUN" position). Codes are not cleared immediately, but will be cleared when the current diagnostic session has been terminated. DTC 12 is never removed and will be displayed at the beginning of each diagnostic session and in between DTC display sequences.

5) Always turn the ignition switch to the "OFF" position before removing the jumper connecting the A and B terminals of the OBD connector. Do not attempt to start or run the engine while the A and B terminals are connected.

 

6.5L GM Diesel OBD I Diagnostic Trouble Code (DTC) List

DTC

Description

DTC

Description

12

Diagnostic system functioning

54

PCM fuel circuit error

13

Engine shutoff solenoid circuit fault

56

Injection pump calibration resistor error

14

Engine coolant temp sensor circuit low (high temp)

57

PCM 5 volt shorted

15

Engine coolant temp sensor circuit high (low temp)

58

Transmission fluid temperature circuit low (high temp)

16

Vehicle speed sensor buffer fault

59

Transmission fluid temperature circuit high (low temp)

17

High resolution circuit fault

61

Turbocharger boost sensor circuit high

18

Pump cam reference pulse error

62

Turbocharger boost sensor circuit low

19

Crankshaft position reference fault

63

Accelerator pedal position 3 circuit high

21

Accelerator pedal position 1circuit high

64

Accelerator pedal position 3 circuit low

22

Accelerator pedal position 1 circuit low

65

Accelerator pedal position 3 circuit out-of-range

23

Accelerator pedal position 1 circuit out-of-range

68

Transmission slip detected

24

Vehicle speed sensor circuit low

69

Torque converter clutch (TCC) stuck "ON"

25

Accelerator pedal position 2 circuit high

71

Cruise control set/coast switch fault

26

Accelerator pedal position 2 circuit low

72

Vehicle speed sensor circuit loss

27

Accelerator pedal position circuit out-of-range

73

Pressure control solenoid circuit error

28

Transmission range pressure switch circuit fault

74

Transmission input speed sensor circuit fault

29

Glow plug relay fault

75

System voltage low

31

EGR control pressure/barometric sensor circuit low

76

Cruise control resume/accel switch fault

32

EGR circuit fault

78

Turbocharger wastegate solenoid fault

33

EGR control pressure/barometric sensor circuit high

79

Transmission fluid over temperature

34

Injection timing stepper motor fault

81

Transmission 2-3 shift solenoid circuit fault

35

Injection pulse width error, short duration

82

Transmission 1-2 shift solenoid circuit fault

36

Injection pulse width error, long duration

83

Torque converter clutch fault

37

Torque converter clutch (TCC) brake switch fault, stuck "ON"

84

Accelerator pedal position circuit fault

38

Torque converter clutch (TCC) brake switch fault, stuck "OFF"

85

Transmission gear error

39

Torque converter clutch (TCC) stuck "OFF"

86

Transmission gear ratio error

41

Brake switch circuit fault

87

Transmission gear ratio error

42

Fuel temperature circuit low (temp high)

88

Top dead center offset error

43

Fuel temperature circuit high (temp low)

91

Cylinder balance fault, cylinder 8

44

EGR pulse width error

92

Cylinder balance fault, cylinder 7

45

EGR vent error

93

Cylinder balance fault, cylinder 6

46

Malfunction indicator lamp (MIL) circuit fault

94

Cylinder balance fault, cylinder 5

47

Intake air temperature sensor circuit low (temp high)

95

Cylinder balance fault, cylinder 4

48

Intake air temperature sensor circuit high (temp low)

96

Cylinder balance fault, cylinder 3

49

Service throttle soon lamp circuit fault

97

Cylinder balance fault, cylinder 2

51

P.R.O.M. error

98

Cylinder balance fault, cylinder 1

52

System voltage high, long

99

Accelerator pedal position sensor reference voltage error (5 volt ref)

53

System voltage high

   

 

Example DTC combination:

SES-----SES-SES-----SES-SES-----SES-SES-SES-SES-SES-----SES-SES-SES-SES-SES-----SES

DTC 12, DTC 25, DTC 51