How to extract trouble codes for OBDI (up to '95)

[97Silverado]

This procedure only works on OBDI vehicles up to '95. Do NOT try this procedure on a 96 or newer vehicle!!

You want to jumper pins A and B. That should be the two upper right pins as you look at the plug.

1. With power off, jumper pin A to pin B

2. Turn the ignition to ON but DO NOT start the vehicle.

3. The Service Engine Soon (SES) light should flash code 12 (1 flash, pause, 2 quick flashes)

4. After a longer pause, code 12 should repeat two more times.

5. If there are any codes stored in the ECM they will follow Code 12.

6. If no other codes have been stored then Code 12 will continue to repeat until the jumper is disconnected.


Remember all OBDI codes are two-digit. I will work on another post to this thread that has a list of codes.

[BigChevMan]

Autozone sells a nifty little tool that looks like a golf divit tool to stick in there. I think they are all of .99..but if you can't afford it..go for the paper clip...it's just hard to do sometimes.

[flacajun]

Just Remember some 94 model S- Trucks were OBDII mostly Blazers and Jimmys but not all if the connector is a square connector it is OBDI if oval in shape and 16 pins it is OBDII

[Timberwolve81]

Engine Codes

I think this is the right list, sorry if it's not, wanna check me on this 97Silverado.

Sorry it's so long, the whole manual can be found on this site if anyone needs it, this is a particular manual for a particular model, but the codes should be the same

it's in PDF format, so make sure you adobe acrobat reader

Code Reader manual

CODE SERVICE CODE DEFINITION

11 (Saturn vehicles ONLY): Indicates transmission service
codes will be displayed next on the "Shift to D2" light
(1991-92 models) or "Temperature" indicator light (1993
and later models)

12 Diagnostic mode; no distributor signal to Electronic
Control Module; System PASS

13 Oxygen sensor signal fault - signal too low / open left
oxygen sensor circuit (Dual sensor models)

14 Coolant sensor or circuit fault - signal voltage low or
shorted

15 Coolant temperature sensor or circuit fault - signal
voltage high

16 Battery or alternator problem - voltage too high or low
Direct ignition system (DIS) fault line open or shorted to
ground
Ignition system fault - loss of 2X or Low Resolution
Pulse signal
Transmission speed error

17 RPM signal problem
Camshaft sensor - circuit problems
Electronic Control Module (ECM) computer circuit
problem - Pull-up resistor (Saturn)

18 Camshaft or Crankshaft sensor - circuit problems
Fuel Injector circuit is not working properly - possible
blown fuel injector fuse

19 Ignition system fault - Intermittent 7X signal or loss of
58X signal or 6X signal (Saturn)

21 Throttle position sensor (TPS) - signal voltage is high

22 Throttle position sensor (TPS) - signal voltage is low
Fuel cutoff relay circuit - open or shorted to ground

23 Manifold air temperature (MAT) sensor - signal voltage
is low or high
Throttle position sensor (TPS) error
Mixture Control (M/C) solenoid - open or short circuit
problems
Intake Air Temperature Sensor (IAT) low
Retrieving ECM Codes

24 Vehicle speed sensor (VSS) - open or short circuit
problems or park/neutral switch circuit problem

25 Manifold air temperature (MAT) sensor - signal voltage
is low or high
Vacuum switching valve circuit open or shorted to
ground
ATS sensor - signal voltage is high or low

26 Quad-Driver module or Quad-driver No. 1 error

27 2nd gear switch problem
Quad-Driver module or Quad-driver No. 2 error

28 3rd gear switch
Quad-Driver module or Quad-driver No. 3 error
(Corvette)
(Transmission) Fluid pressure switch assembly - open or
short circuit problems

29 4th gear switch
Quad-Driver module or Quad-driver No. 3 error
Secondary air injection system - circuit problems

31 Manifold absolute pressure (MAP) sensor - signal
voltage is low
Fuel injector
Park/Neutral switch - circuit problems
CAM sensor - circuit problems
Engine speed control governor malfunction (Van)
Turbocharger wastegate overboost
Wastegate electrical signal - open or shorted to ground
Purge solenoid voltage high (carburetor engines)

32 Barometric pressure (BARO) sensor circuit failure
Exhaust gas recirculation (EGR) valve diagnostic switch -
closed during engine start-up or open when EGR flow
requested by ECM
Electronic vacuum regulator valve (EVRV) error (EVRV
controls EGR vacuum)

33 Mass air flow (MAF) sensor - signal voltage or frequency
is high during engine idle
Manifold absolute pressure (MAP) sensor - signal
voltage is high during engine idle (Note: Engine misfire
or unstable idle may cause this code)

34 Mass air flow (MAF) sensor - signal voltage or frequency
is low during engine cruise
Manifold absolute pressure (MAP) sensor - signal
voltage is low during ignition on
Pressure sensor circuit - signal voltage too high or low
(carburetor engines)

35 Idle air control (IAC) system problem - can not set
desired RPM or idle speed actuator (ISA) carbureted
system problems

36 Mass air flow (MAF) sensor - burn-off circuit problem
Transmission shift problem (electronically controlled
transmissions only)
Direct ignition system (DIS) fault - loss of 24X signal or
extra or missing pulses in electronic spark timing (EST)
signal
Ignition system fault - loss of High Resolution Pulse
signal

37 Brake switch stuck"on"

38 Brake switch circuit fault
Knock sensor (KS) - open circuit problem

39 Torque converter clutch (TCC circuit fault)
Clutch switch circuit problems
Knock sensor (KS) - short circuit problem

41 Cam sensor (CAM) failure
Cylinder select error
Tach input error - no reference pulses during engine run
Electronic spark timing (EST) circuit - open or shorted
to ground during engine run
Direct ignition system (DIS) fault - bypass circuit open
or shorted to ground during engine run
Ignition system fault - loss of 1X Reference Pulse signal
Retrieving ECM Codes

42 Electronic spark timing (EST) circuit - open or shorted
Direct ignition system (DIS) fault - bypass circuit open
or shorted to ground during engine run
Fuel cutoff relay circuit - open or shorted to ground

43 Electronic spark timing (EST) circuit - low voltage
detected
Electronic spark control (ESC) - circuit problems

44 Lean exhaust indicated (Left side on dual oxygen models)

45 Rich exhaust indicated (Left side on dual oxygen
models)

46 Vehicle anti-theft system (VATS) failure
Power steering pressure switch failure

47 Circuit or component problem in ECM/PCM (communication
error)
Knock sensor module error (inside computer)

48 Misfire symptom
Mass air flow (MAF) sensor - circuit error

49 RPM is high at idle (possible vacuum leak)

50 System voltage is low

51 Computer problem; faulty, wrong or incorrectly installed
PROM circuit; or ECM/PCM failure

52 Calibration Package Chip or ECM fault or oil temperature
sensor fault/low engine temperature
(Corvette); faulty or missing PROM/Calibration Package
Chip; ECM problem
System voltage high for a long period of time

53 System voltage too high (over 17.7 volts to ECM) or
EGR system fault or alternator voltage not normal or
Vehicle Anti-Theft System fault

54 Fuel pump circuit fault or Mixture Control (M/C)
solenoid fault or Electronic Control Module (ECM)
fault/EGR solenoid #2 failure (3.8L VIN1)
Fuel pump relay

55 Electronic Control Module (ECM) fault or oxygen sensor
circuit fault or EGR solenoid #3 failure (3.8L VIN1) or
fuel lean monitor (Corvette)

56 Vacuum sensor circuit fault or quad driver "B" fault
(3.8L VIN1)
Corrosivity/add coolant

57 Boost control problem (3.8L VIN1)

58 Vehicle Anti-Theft System fault (3.8L)
Transmission Temperature Sensor (TTS) - short circuit
Transmission fluid temp high

59 Transmission Temp Sensor (TTS) - open
Transmission fluid temp low

60 Transmission not in drive

61 Oxygen sensor signal fault or port throttle system fault
or on-board cruise control fault (vent solenoid circuit)
Air Conditioner (A/C) system performance problems

62 Engine oil temperature sensor fault or gear switch
signal circuit fault or on-board cruise control fault
(vacuum solenoid circuit)

63 EGR flow problem or on-board cruise control problem
Servo Position Sensor (SPS) circuit fault or Manifold
Absolute Pressure (MAP) sensor fault or oxygen sensor
fault

[Timberwolve81]

64 EGR flow problem or on-board cruise control problem or
Manifold Absolute Pressure (MAP) sensor fault or
oxygen sensor fault

65 EGR flow problem or on-board cruise control problem
Servo Position Sensor (SPS) circuit fault or Manifold
Absolute Pressure (MAP) sensor fault or oxygen sensor
fault or fuel injector current low

66 Electronic Control Module (ECM) computer circuit fault
or air conditioning pressure sensor circuit fault or low
air conditioning refrigerant charge
(Transmission) 3-2 shift control solenoid - circuit
problems

67 Cruise control - switch circuit problems
Air Conditioner (A/C) pressure sensor - circuit problems
Torque Converter Clutch (TCC) solenoid - circuit
problems
Cruise control switches - circuit problems
Retrieving ECM Codes

68 On-board cruise control switch circuit problems Servo
Position Sensor (SPS) circuit fault or shorted A/C clutch
relay circuit (Corvette) or overdrive ratio error

69 Air conditioning head pressure switch circuit fault or air
conditioning pressure switch problem
Torque converter clutch stuck "on"

70 Air conditioning refrigerant pressure sensor circuit fault
(high pressure) or quad driver module error

71 Air conditioning evaporator temperature sensor circuit
fault (low temp.)

72 Gear select switch circuit fault - Corvette only
Vehicle Speed Sensor (VSS) - loss of signal

73 Air conditioning evaporator temperature sensor circuit
fault (high temp.)
(Transmission) Pressure control solenoid - circuit
problems

74 Traction control circuit voltage low

75 Digital EGR fault - #1 solenoid or system voltage low
(charging system problem)
Transmission voltage low

76 Digital EGR fault - #2 solenoid

77 Digital EGR fault - #3 solenoid
Primary cooling fan relay driver circuit - circuit
problems

78 Secondary cooling fan relay driver circuit - circuit
problems

79 Vehicle Speed Sensor (VSS) - signal voltage too high
Transmission Temperature Sensor (TTS) - high
temperature

80 Vehicle Speed Sensor (VSS) - signal voltage too low;
transmission component fault

81 QDM Solenoid "B" monitored voltage differs from
commanded
Anti-Lock Brake System (ABS) message fault (Saturn)
Brake switch circuit problems

82 Internal PCM communication fault (Saturn) or QDM
Solenoid "A" monitored voltage differs from commanded
Ignition system fault - 3X signal problem

83 Torque Converter Clutch (TCC) solenoid - circuit
problems
Reverse Inhibit - open or short circuit in reverse inhibit
solenoid

84 3-2 Control solenoid - open or short circuit problems
Skip shift solenoid - open or short circuit problems

85 Programmable Read Only Memory error or undefined
gear ratio (input or output sensor failure)
Torque converter clutch (TCC) - TCC is mechanically
stuck on

86 Analogue/Digital Electronic Control Module (ECM)
error or shift Solenoid "B" stuck on

87 Electrically Erasable Programmable Read Only Memory
(EEPROM) error or shift Solenoid "B" stuck off or high
gear ratio error

88 Electronic Control Module (ECM) computer circuit fault

89 Power Management fault

90 TCC error

91 Skip shift light - open or short circuit problems in skip
shift light circuit

93 Pressure control solenoid - transmission line pressure
not at desired level

95 Change oil light - wrong voltage is present in light
circuit for more than 26 seconds

96 Transmission voltage low - low system voltage possibly
caused by generator voltage supply circuit or power
train control module
Low oil light - wrong voltage is present in light circuit
for more than 26 seconds

97 Vehicle speed sensor (VSS) - output circuit problems

99 Tachometer output circuit problems

[Suburbanite]

Great post! You're just waaaay too dedicated. Thnx.

Hope you don't mind me adding this info to your post but the ABS brake system has separate diagnostics. Here's how to do the ABS system diagnostic test:

Turn the ign switch to the "ON" position. Jump terminal "H" to terminal "A" of the DLC (AKA ALDL) and count the number of "ANTILOCK" lamp flashes. The terminals must be jumped for a few seconds before the DTC (Diagnostic Trouble Code) will begin to flash. Here's an example: if the lamp flashes twice <pause> once, then that indicates DTC 21 which is listed as "Right Front Wheel Speed Sensor or Circuit Open (Static)".

I'm not about to type out the DTCs tho! Sorry. I will provide this much info tho, if the ABS system is working properly then codes 12, 13, 14 or 15 will display depending on whether 2WD/4WD & whether brake pedal is released/applied.

Here's the procedure for clearing ABS codes:
1. Turn the ign switch to the "ON" position.
2. Use a jumper wire to ground DLC terminal "H" to "A" for 2 seconds.
3. Remove the jumper wire for 1 second.
4. Repeat the grounding for 2 seconds.
5. An indication of success is when the "ANTILOCK" and "BRAKE" lamps turn on and then turn off.

All of the above is directly from my '95 FSM.

Pin A, the ground, is the topmost right corner pin & pin H is one pin over from the bottom left corner.

[kevinwebster1]

i have a 93 silverado and sometimes the SES light comes one. i went ahead and spent 25 bucks for the actual gm diagnostic code thing. i was wondering if the code 12 will always flash first. like mine reads...12, 12, 12, then 32, 32, 32. is 12 nothing important? you wouldnt happen to knwo how to fix 32 would you? i read what 32 was i just dont know how to fix it.

[flacajun]

12 means the system is functing 32 is an egr code

[LOWGREEN1]

I thought I would add a little to this. You can go into "Field Service" mode by grounding the A&B pins and starting the engine. In this mode, the SES light will indicate whether the system is in Open or Closed loop. In Open Loop the SES light flashes two and one-half times per second. In Closed Loop the SES light flashes once per second. Also in Closed loop the light will stay OFF most of the time if the system is running Lean. It will stay ON most of the time if the system is running Rich. While in the Field service mode new codes cannot be stored and the closed loop timer is bypassed.

[hamdave]

I have read a lot of good info here. I have written a very basic program using Visual C++ to allow me to talk to my GM motorhome chassis vehicle. I am still testing the program and only have a few of the commands to play with. Is there a list of command/responses available somewhere??
I am retired software/process engineer and do this to keep myself
current and also learn how to take care of my investment. Mine is a GM 454, on a P30 '95' chassis. I probably will NOT be modifying my Ecm for now, but one never knows.
My next effort will be to place my monitor in between my elmscan and my newer vehicles and use it to trap all the message activity as I learn about them as well.
I do this stuff as a hobby only, along with ham radio and a few other toys I have.

thanks.
kd8w

[aandllandscapes]

Ok here you have some good info but now how can i fix code 54 in my truck

[Nicklessig]

The codes are slightly different according to which transmission you have. I learned this when replacing my knock sensor.