For 1990-2009 cars

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Lack of communication may be due to a partial or total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.

2. The presence of DTCs indicates that the PCM or TAC Module has detected a fault.

3. 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.

4. This step insures that the PTO options in the scan tool are set according to the upfitters recommendations.

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 powertrain control module (PCM) for the 8.1L engine.

Does the scan tool communicate with the control module?

Go to Step 3

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

3 | Select the display DTCs function on the scan tool. Does the scan tool display any PCM DTCs? | Go to Step 4 | Go to Step 5
4 | Does the scan tool display any DTCs which begin with a "U"? | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | Go to Diagnostic Starting Point - Engine Controls in Engine Controls 8.1L or Diagnostic Starting Point - Cruise Control in Cruise Control
5 | View the PTO options on the scan tool to verify that the PTO settings are correct for the specific PTO application. Are the PTO settings correct? | Go to Symptoms - Power Take-Off (PTO) | Go to Step 6
6 | Change the PTO options as needed. Refer to the upfitter specifications in the upfitter installation manual. Are the PTO options set correctly? | Go to Symptoms - Power Take-Off (PTO) | --