OBD1 Codes – Trouble Code List & reading (GM)

Did you own a GM car from 1980-1995? There is a good chance that your vehicle has an OBD1 connector.

It is unique, it works on Pontiac Chevrolet GMC Oldsmobile Cadillac and Buick. You can use the OBD1 connector to read trouble codes from your vehicle at home, without needing any diagnostic tools.

These connectors can be read without the use of special diagnostic tools.

OBD2 codes are found in newer cars after 1996. This article won't apply to them. Our other OBD2 code article is available.

Índice de Contenido
  1. Check out the OBD1 Trouble Codes List
  2. OBD1 Connector Locator
  3. Pinout of OBD1 Connector Wirings
  4. How to Access OBD1 Codes from Home
  5. OBD1 Code Reader

Check out the OBD1 Trouble Codes List

This is an exhaustive OBD1 trouble code listing. The OBD1 codes’ meanings can differ a bit depending on what car model you have, but most of them are the same among all car manufacturers. These codes are not to be considered as a warranty. For the specific trouble codes for your vehicle model, check your manual.

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

OBD1 Connector Locator

Obd1 Connector

The OBD1 connection is located underneath your steering wheel. Sometimes, the OBD1 connector might have a cover made of black plastic that you will need to take off before you can get access. It is usually black with 12 pins. This connector can be identified easily.

Take a look at the photo above to see how an OBD1 connector appears.

Pinout of OBD1 Connector Wirings

Although the OBD1 connector contains 12 pins (not all) they are utilized in many car models. However, the standard pins such as ground, power and diagnostic are identical in all car models.

Make sure you connect your wires correctly, as if you are not careful, it may damage your vehicle’s electrical system and control units, which can be very expensive.

Here is the OBD1 connector pinout in most cars. Check your manual to see the exact pinout.

Obd1 Pinout

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How to Access OBD1 Codes from Home

Obd1 Jump Wire

The easiest way to read without using a diagnostic tool, is to shorten the pin A/pin B circuits. The car will then enter the diagnostic mode and flash the “check engine Light” several times, and we should count the flashes to figure out the diagnostic codes.

How to find the OBD1 codes

  1. If you need to do any type of electrical work that involves the ignition, make sure to connect your car battery charger. The low voltage could cause many problems with troubleshooting, as well as error codes that are not desired.
  2. Place a jumper cable between PIN A & PIN B.
  3. Turn the ignition ON and let the jumper cable rest. Don't start the engine.
  4. You will see the check engine lamp flash. Keep counting the flashes. There will be a longer pause between the codes if you have several trouble codes and a shorter pause between the trouble codes’ digits. For example, code 16 = 1 flash * Pause * 6 flashes.
  5. When all trouble codes are outputted, it will flash the code 12 – 1 flash * Pause * 2 flashes.
  6. Note down the problem codes you received and then check the table below.
  7. Take out the jumper wires and car battery charger.

OBD1 Code Reader

Obd1 Code Reader

OBD1 codes readers are available in many sizes and colors to simplify your job. An OBD1 code scanner does not require you to cut the connector and it doesn't count flashes.

This will let you know the issue in plain text. It is a good investment if your vehicle has a lot trouble codes.

There are many code scanners available on the market, all at different prices. Although some scanners have the ability to read OBD1 codes and OBD2 code, these can be very expensive. The Innova 3123 scanner is a great option. There are two options available: GM or Ford vehicles. You can also find the scanner on Amazon if you'd like to have a closer look.

Innova 3123 Gm Obd1 Code Reader

INNOVA 3123 GM OBD1 Code Reader

  • You can safely access the onboard computer from anywhere in the world to...
  • It works on all domestic General Motors vehicles
  • It connects to the vehicle's computer...
  • It will not cause any damage to the computer in your vehicle...

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