Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Test Description
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Test Description
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers on the diagnostic table.
- 4: This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with the Power Train Control Module (PCM), then the DLC ground circuit (terminal 4) and the DLC ignition positive voltage circuit (terminal 16) are OK.
- 5: This step checks for an open in the serial data circuit between the SDM and the right instrument panel junction block or for a defective SDM.
- 6: This step checks for an open/short to ground circuit, a short to battery positive circuit, or for a defective scan tool.
- 7: The modules supply a low current (about 1.85 mA) on the serial data circuit. The normal circuit low current will NOT illuminate a test lamp. If the circuit is shorted to battery positive the higher current will illuminate the test lamp.
- 10: The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Verify the scan tool for proper operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.
Scan Tool Does Not Communicate with SDM
| Step | Action | Value | Yes | No |
|---|---|---|---|---|
| Schematic Reference: Data Link Connector (DLC) Schematics and SIR Schematics in SIR |
||||
| 1 | Did you perform the Diagnostic System Check - Engine Controls ? | - | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
in Engine Controls 1.8L (LV6) or Diagnostic System Check - Engine Controls in Engine Controls 1.8L (LNK) |
| 2 |
|
- | System OK | Go to Step 3 |
| 3 | Is the vehicle equipped with ABS? | - | Go to Step 4 | Go to Step 5 |
| 4 | Attempt to establish communication with the antilock brake system (ABS) module. Does the scan tool display the brake pressure modulator valve (BPMV) data? |
- | Go to Step 5 | Go to Step 6 |
| 5 |
|
- | Go to Step 2 | Go to Step 12 |
| 6 |
|
11 V | Go to Step 7 | Go to Step 8 |
| 7 | Connect a test lamp between the DLC connector terminal 7 and ground. Does the test lamp illuminate? |
- | Go to Step 10 | Go to Step 11 |
| 8 |
|
- | Go to Step 2 | Go to Step 9 |
| 9 |
|
- | Go to Step 2 | - |
| 10 | Repair the short to battery positive voltage in the serial data circuit. Refer to Wiring Repairs
in Wiring Systems. Scan tool damage may have occurred. Is the action complete? |
- | Go to Step 2 | - |
| 11 | Replace the defective scan tool. Is the action complete? |
- | Go to Step 2 | - |
| 12 | Inspect for poor connections at the harness connector of the SDM. Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 2 | Go to Step 13 |
| 13 | Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement
. Is the action complete? |
- | Go to Step 2 | - |
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.