For 1990-2009 cars

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 heater, the ECM, and A/C control unit.

Does the scan tool communicate with the heater and A/C control unit?

Go to Step 3

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

3 | Select the Heating and Air Conditioning display DTCs function on the scan tool. Does the scan tool display any DTCs? | Go to DTC Table | Go to Symptoms