Circuit Description
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 for the scan tool through the DLC. The Keyword 2000 serial data circuit to the DLC allows the ECM to communicate with the scan tool. A universal asynchronous receiver transmitter (UART) serial data line is used to communicate with the other modules such as the electronic brake control module (EBCM), the supplemental inflatable restraint (SIR) system, and the instrument panel cluster (IPC).
Diagnostic Aids
Notice: Refer to Defective Scan Tool Notice in the Preface section.
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-wire connection |
| • | Physical damage to the wiring harness |
| • | Corrosion |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The On-Board Diagnostic (EOBD) System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
-
Unlike the UART serial data circuit, the only time a class 2 serial data circuit has any voltage on it is when a scan tool asks the ECM for information and sends the information out.
-
Locate and repair any shorts that may have caused the fuse to open before replacement, if the no voltage condition was due to an open fuse.
-
The scan tool or associated cables could be malfunctioning. Refer to the scan tool manual for repair information.
Step | Action | Yes | No |
|---|---|---|---|
Perform an On-Board Diagnostic (EOBD) System Check. Was the check performed? | Go to Step 2 | ||
With a test light connected to the ground, probe the data link connector (DLC) battery feed terminal 16. Does the test light illuminate? | Go to Step 4 | Go to Step 3 | |
3 | Repair an open or short to ground in the DLC battery feed circuit. Is the repair complete? | Go to Step 4 | -- |
4 | With a test light connected to the battery, probe the DLC ground terminal 4 and 5. Does the test light illuminate? | Go to Step 6 | Go to Step 5 |
Repair an open circuit. Is the repair complete? | Go to Step 6 | -- | |
6 |
Does the scan tool power up? | Go to Step 8 | Go to Step 7 |
7 | Inspect for damages in the terminal of DLC and scan tool, and repair as needed. Is the repair complete? | Go to Step 8 | -- |
8 | Using a scan tool, request engine data of engine control module (ECM). Does the scan tool display any data? | Go to Step 12 | Go to Step 9 |
9 | Install the scan tool on another vehicle and check for proper operation. Does the scan tool work properly on a different vehicle? | Go to Step 11 | Go to Step 10 |
The scan tool is malfunctioning. Refer to the scan tool manual for repair. Is the repair complete? | Go to Step 12 | -- | |
11 | Repair the communication circuit between the ECM and DLC. Is the repair complete? | Go to Step 12 | -- |
12 |
Does the engine start and continue to run? | Go to Step 13 | Go to Step 2 |
13 |
Are any DTCs displayed that have not been diagnosed? | Go to applicable DTC table | System OK |
