Chevrolet OBD1 Trouble Codes

The following trouble codes are specific to Chevrolet. You may also see GMC and other GM brands, since Chevrolet and GMC are of the same parent company.

Chevrolet Trouble Codes Access

If you have a GM vehicle between 1980 to 1995, there is a big chance your car has an OBD1 connector (ALDL).

This connector is unique and applies to Pontiac, Chevrolet, GMC, Oldsmobile, Cadillac, and Buick, and more. The good thing with the OBD1 connector is you can read your trouble codes at home without any diagnostic tools.

There are special diagnostics tools for this kind of connector, but they are not necessary as you can read them just as well without a tool.

Without OBD Scan Tool

To access the trouble codes, proceed as follows:

• Turn ignition switch to off position
• Locate Data Link Connector (DLC)
• Jumper the A and B terminals (a paper clip or a jumper wire work ok)
• Turn ignition switch to on position.
• Count the flashes on the "check engine" or "service engine" light.
• Flash, pause, flash, flash, flash, flash = code 14

Note: Some 1994 and 1995 models do not have the B terminal. In which case an OBD1 scanner is required.
Note: Some 1994 and 1995 models that do have the A and B terminals still require an OBD1 scanner.

All vehicles after 1996 are OBD2,and require a scanner to access the trouble codes.

Chevrolet Trouble Codes Clearance

All trouble codes must be cleared from the ECU’s memory after repairing the faults. Otherwise, code(s) would remain in the ECU’s memory indefinitely and would appear along with a new code in the event of a future problem. To clear the trouble codes, proceed as follows:

• Turn the ignition key to position off.
• Disconnect the battery negative terminal for at least 20 seconds and the ECU (ECM) memory will be erased.
• Reconnect the battery negative terminal and check the codes to confirm the repair.

Warning: Disconnecting the battery may erase memory from electronic units, e.g., clock, radio.

Chevrolet Generic Trouble Codes

Code(s)	Description
12	System OK (Diagnosis mode active)
13	Oxygen O2 Sensor – Circuit open/no activity
14	Coolant Temperature sensor – Resistance too high or shorted circuit
15	Coolant Temperature Sensor – Circuit low or open
16	Direct ignition system (DIS) – Faulty circuit / shorted circuit
17	Camshaft Position Sensor – Circuit/timing error
18	Camshaft or Crankshaft – Sensor/circuit/timing error
19	Crankshaft sensor – Sensor/circuit/timing error
20	Fuel Pump Circuit (open)
21	Throttle position sensor – Out of range/Performance
22	Throttle position sensor – Low Voltage
23	Intake Air temp sensor – Out of range, low resistance
24	Vehicle speed sensor – Circuit fault
25	Intake Air temp sensor – Out of range, high resistance
26	QDM A (Quad-driver module) – Circuit #1 fault
27	QDM A (Quad-driver module) – 2nd gear circuit
28	QDM A (Quad-driver module) – Circuit #2 fault
29	QDM A (Quad driver module) – 4th gear circuit
31	Wastegate solenoid – Circuit fault
32	EGR (Exhaust Gas Recirculation) – Circuit fault
33	Manifold Air Pressure Sensor – Signal out of range, high resistance
34	Manifold Air Pressure Sensor – Signal out of range, low resistance
35	Idle air control valve / Sensor – Circuit fault
36	Ignition system – Circuit error/fault
37	MAT sensor temp high (3.8L). Brake switch(4L60-E trans)
38	Brake input (Brake switch sensor) – Circuit fault
39	Clutch input (Clutch sensor) – Circuit fault
40	Power steering pressure switch
41	Camshaft sensor – Circuit fault or ignition control – circuit fault/error (depending on the car model)
42	EST (Electronic spark timing) – Circuit grounded/shorted
43	Knock sensor / Electronic spark control – Circuit fault error (depending on the car model)
44	Oxygen O2 sensor – Lean Mixture
45	Oxygen O 2sensor – Rich Mixture
46	Pass-key II – Circuit or Power steering pressure switch – circuit fault error (depending on the car model)
47	PCM data – Circuit error
48	Misfire (diagnosis)
51	Calibration error – Mem-cal, ECM, or EPROM failure
52	Engine oil temperature circuit – Low temperature indicated / circuit error
53	Battery voltage – Low/high/error or Egr valve solenoid 1 – circuit error (depending on the car model)
54	Fuel Pump – Circuit error or Egr valve solenoid 2 – Circuit error (depending on the car model)
55	ECM PCM – Circuit error or EGR valve solenoid 3 – Circuit error (depending on the car model)
56	Quad-driver module (QDM B) – Circuit error
57	Boost control – Error / Faulty
58	Vehicle anti-theft system (VATS) – Circuit faulty
59	Trans code-TTS temp low
61	AC (Air conditioning) system performance or degraded oxygen sensor signal (depending on the car model)
62	Engine oil temperature sensor – High temperature indicated
63	Oxygen O2 sensor right side – Circuit open or MAP (manifold air pressure sensor) – out of range (depending on the car model)
64	Oxygen O2 sensor right side – Lean mixture indicated
65	Oxygen O2 sensor right side – Rich mixture indicated
66	A/C (Air conditioning) pressure sensor – Circuit low pressure
67	A/C (Air conditioning) pressure sensor – Circuit or a/c clutch – circuit failure (depending on the car model)
68	A/C (Air conditioning) compressor relay – Circuit failure error
69	A/C (Air conditioning) clutch – Circuit/pressure high
70	A/C (Air conditioning) refrigerant pressure – Circuit high
71	A/C (Air conditioning) evaporator temperature sensor – circuit low
72	Gear selector switch – Circuit error/fault
73	A/C (Air conditioning) Evaporator temperature – Circuit high
74	Trans input speed error (4L80-E)
75	Digital EGR #2 – Solenoid error/faulty
76	Digital EGR #3 – Solenoid error/faulty
77	Digital EGR #1 – Solenoid error/faulty
79	Vehicle speed sensor (SS) – Circuit signal high resistance
80	Vehicle speed sensor (VSS) – Circuit signal low resistance
81	Brake input data – Circuit faulty
82	Ignition control (IC) 3X – Signal error/faulty circuit
83	TCC solenoid circuit fault
85	Prom – Error/faulty circuit
86	Analog/digital – Pcm error /faulty circuit
87	Eprom – Error / faulty circuit
99	Power management – Error / faulty circuit