Is there a procedure to retrieve engine fault codes from a 1994 Chevy S10 without a scan tool?

Answer 1

Assuming you have located the ALDL (Assembly Line Data Link) under the left side of the dash, with the engine off, connect the A and B terminals (or the #5 and #6 terminals in the case of an OBD-I vehicle with the 16 pin OBD-II style connector) with your trusty paper clip. WITHOUT STARTING THE ENGINE, turn the key to the 'run' position and watch the "check engine" light. All GM codes are 2 digit, and each code will repeat three times before moving on to the next stored code. The format is "first digit, short pause, second digit, long pause", and the fact that each code is repeated three times makes it easy to figure out. The first and last code you'll get is "12", which indicates that the computer is in diagnostic mode. If you only get code 12, there are no faults stored in the system.

GM common codes for OBD1 (for vehicles made before 1995)

12 System normal

13 oxygen sensor circuit open

14 coolant sensor high resistance or shorted

15 coolant sensor circuit low or open

16 direct ignition system (DIS) fault in circuit

17 cam position sensor fault

18 crank or cam sensor error

19 crank sensor circuit fault

21 tps sensor out of range

22 tps sensor signal voltage low

23 intake air temp sensor out of range, low

24 vehicle speed (vss) sensor circuit fault

25 air temp sensor sensor out of range, high

26 quad-driver module (computer) circuit #1 fault

27 quad-driver module (computer) 2nd gear circuit

28 quad-driver module (computer) circuit #2 fault

29 quad driver module (computer) 4th gear circuit

31 cam position sensor fault

32 egr circuit fault

33 map sensor signal out of range, high

34 map sensor signal out of range, low

35 idle air control sensor circuit fault

36 ignition system circuit error

38 brake input circuit fault

39 clutch input circuit fault

41 cam sensor circuit fault, igntion control circuit fault

42 electronic spark timing (EST) circuit grounded

43 knock sensor

or electronic spark control circuit fault

44 oxygen sensor lean exhaust

45 oxygen sensor rich exhaust

46 pass-key II circuit or ps.pressure switch circuit fault

47 pcm-bcm data circuit

48 misfire diagnosis

51 calibration error, mem-cal, ecm or eeprom failure

52 engine oil temperature circuit, low temperature indicated

53 battery voltage error or egr or pass-key II circuit

54 egr system failure or fuel pump circuit low voltage

55 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage

56 quad-driver module #2 circuit

57 boost control problem

58 vehicle anti-theft system fuel enable circuit

61 a/c system performance or degraded oxygen sensor signal

62 engine oil temperature high temperature indicated

63 oxygen sensor right side circuit open or map sensor out of range

64 oxygen sensor right side lean exhaust indicated

65 oxygen sensor right side rich exhaust indicated

66 a/c pressure sensor circuit low pressure

67 a/c pressure sensor circuit or a/c clutch circuit failure

68 a/c compressor relay circuit failure

69 a/c clutch circuit head pressure high

70 a/c refrigerant pressure circuit high

71 a/c evaporator temperature sensor circuit low

72 gear selector switch circuit

73 a/c evaporator temperature circuit high

75 digital egr #1 solenoid error

76 digital egr #2 solenoid error

77 digital egr #3 solenoid error

79 vehicle speed sensor (vss) circuit signal high

80 vehicle speed sensor (vss) circuit signal low

81 brake input circuit fault

82 ignition control (IC) 3X signal error

85 prom error

86 analog/digital ecm error

87 eeprom error

99 power management