The on-board diagnostic (OBD) system on pre-1996 Chevrolet S10 and GMC S15/Sonoma vehicles can display the trouble codes stored in the fuel injection computer by connecting two diagnostic link connector (DLC) terminals.
In this tutorial, I'll show you the location of the DLC and the specific terminals that need to be connected in order to retrieve the diagnostic trouble codes (DTCs) that are causing the check engine light (CEL) to come on.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Leer Los Códigos De Falla (2.8L V6 GM) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.8L Chevrolet S10 Blazer: 1988, 1989.
- 2.8L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
- 2.8L GMC S15 Jimmy: 1986, 1987, 1988, 1989.
- 2.8L GMC S15 Pickup: 1986, 1987. 1988, 1989, 1990.
- 2.8L GMC Sonoma: 1991, 1992, 1993.
Reading The On/Off Flashes Of The Check Engine Light
The diagnostic link connector can typically be found under the dashboard, usually on the right side of the steering wheel column.
In GM terminology, the Diagnostic Link Connector (DLC) is also known as the Assembly Line Data Link (ALDL) connector.
The connector is the same on all GM vehicles manufactured before the implementation of OBD II. The image at the beginning of this tutorial shows how the ALDL connector looks like.
You can use a paper-clip or a small piece of wire (with both ends stripped) to 'jumper' these two terminals together.
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.
- 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 |
16 | Transmission Speed Error |
21 | TPS Signal Voltage High |
22 | TPS Signal Voltage Low |
23 | MAT (Manifold Air Temperature) Signal Voltage High (2.5L Only) |
24 | Vehicle Speed Sensor (VSS) Signal Voltage High |
25 | MAT (Manifold Air Temperature) Signal Voltage Low (2.5L Only) |
26 | Quad Driver 1 Fault (4.3L M/T only) |
27 | Quad Driver 2 Fault (4.3L M/T only) |
28 | Transmission Pressure Switch Manifold Range Circuit Problem |
32 | EGR System Failure |
33 | MAP Sensor Signal Voltage High |
34 | MAP Sensor Signal Voltage Low |
35 | Idle Speed Error |
37 | Brake Switch Stuck On (4L60-E A/T only) |
39 | Knock Sensor Circuit Shorted (4.3L M/T Only) |
42 | Electronic Spark Timing (EST) Fault |
43 | Electronic Spark Control (ESC) Fault |
44 | Lean Exhaust |
45 | Rich Exhaust |
51 | PROM/MEM-CAL Fault |
51 | System Voltage High (Charging System Problem) |
54 | Fuel Pump Circuit |
54 | Faulty ECM/PCM/VCM |
More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:
Here's a sample of the articles, you'll find in the Index of Articles:
- How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).
If this info saved the day, buy me a beer!