Circuit Description
Caution: Refer to Defective Scan Tool Notice in the Preface section.
The provision for communicating with the engine control module (ECM) is the data link connector (DLC). It is located under the instrument panel. The DLC is used to connect the scan tool. Battery power and ground is supplied to the scan tool through the DLC. The serial data circuit to the DLC allows the ECM and the transmission control module to communicate with the scan tool. A universal asynchronous receiver transmitter (UART) serial data line is used to communicate with the supplemental inflatable restraint (SIR) system. Other serial data lines communicate with the electronic brake control module (EBCM) and the speed sensitive power steering (SSPS) module.
Diagnostic Aids
Ensure that the correct application, model line, car year, etc., has been selected on the scan tool. If communication still cannot be established, try the scan tool on another vehicle to ensure that the scan tool or cables are not the cause of the condition.
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation.
Any circuitry that is suspected of causing an intermittent complaint should be thoroughly inspected for the following conditions:
| • | Backed-out terminals |
| • | Improper mating of terminals |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal-to-wiring connection |
| • | Physical damage to the wiring harness |
| • | Corrosion |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Data Link Connector Schematics | |||
1 | With a test light connected to ground, probe the data link connector (DLC) battery feed terminal 16. Does the test light illuminate? | Go to Step 3 | Go to Step 2 |
2 | Repair an open or short to ground in the DLC battery feed circuit. Is the repair complete? | Go to Step 3 | -- |
3 | With the test light connected to the battery, probe the DLC ground terminal 4. Does the test light illuminate? | Go to Step 5 | Go to Step 4 |
4 | Repair an open circuit. Is the repair complete? | Go to Step 5 | -- |
5 |
Does the scan tool power up? | Go to Step 7 | Go to Step 6 |
6 | Inspect for damages in the terminal of the DLC and scan tool, and repair as needed. Is the repair complete? | Go to Step 7 | -- |
7 | Using a scan tool, request engine data of the engine control module (ECM). Does the scan tool display any data? | Go to Step 11 | Go to Step 8 |
8 | Install the scan tool on another vehicle and inspect for proper operation. Does the scan tool work properly on a different vehicle? | Go to Step 10 | Go to Step 9 |
9 | The scan tool is malfunctioning. Refer to the scan tool's manual for repair. Is the repair complete? | Go to Step 11 | -- |
10 | Repair the communication circuit between the ECM and the DLC. Is the repair complete? | Go to Step 11 | -- |
11 |
Does the engine start and continue to run? | Go to Step 12 | Go to Step 1 |
12 |
Are any DTCs displayed that have not been diagnosed? | Go to applicable DTC table | System OK |
