In this tutorial, I'll explain how to retrieve OBD I diagnostic trouble codes by bridging (jumpering) two diagnostic link connector (DLC) terminals.
You'll also find a Diagnostic Trouble Codes chart with a description of each diagnostic trouble code.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Leer Los Códigos De Avería OBD I (1989-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1987, 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Reading The On/Off Flashes Of The Check Engine Light
The diagnostic link connector is located under the dash, usually on the right side of the steering wheel column.
The diagnostic link connector (DLC) is known as the Assembly Line Data Link (ALDL) connector in GM tech speak. In the photo at the beginning of this tutorial, you can see what the ALDL connector looks like.
These are the steps to retrieve the trouble codes:
- Make sure your battery is fully charged before starting (its customary to place a charger on the battery while retrieving trouble codes to keep the battery from discharging).
- Turn the key to the ON position but don't start the vehicle.
- Jumper terminals A and B of the diagnostic link connector together (you can use a paperclip for this).
- If no trouble codes are present:
- The MIL will flash a code 12 (see illustration below) which consists of one flash, a short pause, then two flashes in rapid succession. Code 12 would look like this:
- 'Flash', pause, 'flash', 'flash', long pause.
- Code 12 will is repeated another 2 times (all codes are flashed 3 times before the next one).
- The MIL will flash a code 12 (see illustration below) which consists of one flash, a short pause, then two flashes in rapid succession. Code 12 would look like this:
- If trouble codes are present:
- The MIL will flash code 12 three times and then any other codes stored.
- Each trouble code, in addition to code 12, is flashed 3 times.
- A code 22 would look like this:
- 'Flash', 'flash', pause, 'flash', 'flash', long pause.
Once you've confirmed and written down the trouble codes, remove the jumper wire from the diagnostic link connector (DLC) and turn the key to the Off position.
GM OBD I Diagnostic Trouble Code Definitions
| Chevy S10/GMC S15 OBD I Trouble Code Definitions | |
|---|---|
| Code | Description |
| 12 | System Check |
| 13 | Oxygen Sensor Circuit |
| 14 | Engine Coolant Temperature (ECT) High Temperature Indicated |
| 15 | Engine Coolant Temperature (ECT) Sensor Signal Voltage High |
| 21 | TPS Signal Voltage High |
| 22 | TPS Signal Voltage Low |
| 23 | MAT (Manifold Air Temperature) Signal Voltage High |
| 24 | Vehicle Speed Sensor (VSS) Signal Voltage High |
| 25 | MAT (Manifold Air Temperature) Signal Voltage Low |
| 32 | EGR System Failure |
| 33 | MAP Sensor Signal Voltage High |
| 34 | MAP Sensor Signal Voltage Low |
| 35 | Idle Speed Error |
| 42 | Electronic Spark Timing (EST) Fault |
| 44 | Lean Exhaust |
| 45 | Rich Exhaust |
| 51 | PROM/MEM-CAL Fault |
| 53 | System Voltage High (Charging System Problem) |
| 54 | Fuel Pump Circuit |
More 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of 2.5L Chevy S10 pickup, GMC S15 pickup, And GMC Sonoma tutorials here:
Here's a sample of the tutorials you'll find in the index:
- How To Test Engine Compression (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test For A Blown Head Gasket (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The MAP Sensor (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
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