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2,428 Posts
Discussion Starter #1
These are the GM specific OBD1 DTC codes:

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

4 Posts
On obd1 cars you need to change the chip inside the computer, call summit racing or Jeggs to see if one is offered for your engine.

6 Posts
anybody got the codes for the 98 GMC 1500 5.7 ... Just asking Thanks Guys. More Checy to ya!

322 Posts
:rules: Do you have the codes for the 98 GMC 5.7 Vortec
'96 & up is OBD II and you need a reader to get them...OBD I you could get w/ a paper clip by making the CES lamp flash ' GM OBD II Codes

67 Posts
'96 & up is OBD II and you need a reader to get them...OBD I you could get w/ a paper clip by making the CES lamp flash ' GM OBD II Codes
So this ODB ‘scanner’ I bought years ago is just a paper clip in disguise???

That’s too funny… at least having the book with all the codes comes in handy!

5 Posts
A friend of mine just got back from Autozone...They can't scan the OBD 1 vehicles anymore because their scanner doesn't work on them...ha I whipped out my scanner (paperclip) and did it for him...too funny.

2 Posts
I just got a 1992 C1500, 4.3, with a 5-speed. Every once in a while the check engine light comes on, usually after driving on the freeway, and when I turn the truck off the light doesn't come back on. I went out and bought an OBD1 reader for it, problem is that the truck has to be be off to read the code, and as I previously stated, it stops throwing the code as soon as I turn the truck off. The EGR is plugged off, there's a small leak from the oil sending unit and the truck has 289,000miles and the original cat(OBD1 so no after cat O2 sensor.) Any ideas or suggestions?

27 Posts
I own a 1994 Fleetwood Southwind Storm (28ft) on a P-30 chassis and had the following issue resolved....

While on my trip (Seattle to HB, Ca. early 07/2017) I had a trans slip issue start up while on the last leg of the pass just south of Ashland, Oregon. After cresting the RV would not go beyond 30-35mph (2-3 gear). Pull off at Yreka, Ca. stayed the night (Baxters Auto lot). While parked I clean all engine/trans ground braids and battery terminal/s.

The next morning they sent me over to Onarheim truck repair. Mechanic checked what I had checked (fluid) which was perfect no issue. He also drove it without issue. Says it may have gotten hot but unsure.

Continue on south. Made it to HB, Ca. (shot over from the 5 to the 101 via 505 - 680 - 101). No issue/s.

On the return trip ~10 days later just south of Willits, Ca. (after a pass climb) I had it do the same thing again. This was after driving without issue from Huntington Beach, Ca.

Same results next morning no issue. However roughly 35 miles later same issue popped up (after small climb). This time I could tell the trans was in limp mode. Not going from 2-3. Quickly realizing that when turning of the engine and restarting it resets and all is ok. Now beginning to look like shift solenoid issue. Did this (3 times) until I reached Grants Pass, Oregon and stopped the night. Ended up staying just outside of Jerry's Clutch & Transmission (Great guy). While stopped I used paper clip to pull codes 68 and 87.

The following morning (Joe) mechanic used hand held Sun computer and pulled same codes:

68 - Trans slip
87 - Shift solenoid stuck open

He quickly fixed it by stating the 68 slip can be resolved by turning the force valve up 1/4 turn and also replace both shift solenoids A & B and the wiring harness which showed signs of leakage into the connector (likely causing my issue).

Back on the road in roughly 2-3 hours.

So if anyone ever has trans issue I highly recommend Jerry's Clutch & Transmission in Grants Pass, Or.

The codes he pulled off his Sun hand held differed from the codes shown on your post. The following is the vin #1GBJP37N4R3314754
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