For 1990-2009 cars

### Description

The Cruise Control Diagnostic System Check is an organized approach to identify a condition created by an electronic control system malfunction. The Diagnostic System check directs the service technician to the next logical step in diagnosing the concern. Understanding the system, the table and using it correctly reduces diagnostic time and prevents misdiagnosis. For a review of the cruise control system refer to Cruise Control Description and Operation .

### Test Description

The numbers below refer to the step numbers 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 Data Line in Data Link Communications

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

• | P0571

• | P1662

Go to Diagnostic Trouble Code (DTC) List

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 - Cruise Control