For 1990-2009 cars

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. Lack of communication may be due to a malfunction of the Keyword serial data circuit. The specified procedure will determine the particular condition.

2. The presence of DTCs which begin with U indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to Scan Tool Does Not Power Up in Data Link Communications
2 |

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the Engine Control Module (ECM).

Does the scan tool communicate with the ECM?

Go to Step 3

Go to Scan Tool Does Not Communicate with Keyword 82 Data Line in Data Link Communications

3 | Select the ECM DTCs function on the scan tool. Does the scan tool display any of the following DTCs?

• | P0571

• | P0603

• | P1662

Go to DTC List in Engine Controls

Go to Step 4

4 | Does the scan tool display any DTCs which begin with a "U"? | Go to Diagnostic Trouble Code (DTC) List in Data Link Communications | Go to Symptoms