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 1A: Identifying Vehicle Communication Problems
Connect scan tool to Data Link Connector (DLC) to retrieve Diagnostic Trouble Codes (DTC) and bus failure messages. If scan tool message is blank, see NO RESPONSE DIAGNOSIS table and proceed to appropriate test number. Disconnect scan tool. Ensure ground circuit has continuity at DLC terminals No. 4 and 5. Ensure 12 volts is present at DLC terminal No. 16. Try another scan tool and/or cable. See NO RESPONSE DIAGNOSIS , BUS FAULT MESSAGES and BUS SYMPTOMS tables and proceed to appropriate test number.
| Problem Module | Test No. | ||
|---|---|---|---|
| Air Bag Control Module (ACM) | 2A | ||
| Automatic Temperature Control (ATC) | 3A | ||
| Body Control Module (BCM)(1) | 4A | ||
| Anti-Lock Brake Module | 5A | ||
| Mechanical Instrument Cluster (MIC) | 6A | ||
| Memory Heated Seats (MHS) | 7A | ||
| Overhead Traveler Information System (OTIS) | 8A | ||
| Powertrain Control Module (PCM) | 9A | ||
| Radio | 10A | ||
| Sentry Key Immobilizer (SKIM) | 11A | ||
| Transmission Control Module (TCM) | 12A | ||
|
|||
| Fault Messages | Test No. |
|---|---|
| BUS SHORT TO BATTERY | 13A |
| BUS SHORT TO GROUND | 14A |
| Symptom Messages | Test No. |
|---|---|
| Odometer Displays NO BUS | 15A |
| No Fused Ignition Switch Output To BCM | 16A |
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.