The ECM detects a short to voltage on the control circuit of the A/C compressor clutch relay.
Action Taken When the DTC Sets
- The ECM will not illuminate the malfunction indicator lamp (MIL).
- The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.
Conditions for Clearing the DTC
- A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
- The DTC can be cleared by using a scan tool.
Diagnostic Aids
| IMPORTANT | Be sure to verify that the ECM engine grounds are secure and clean. |
If DTC P0645, P0646, P0647 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 2: Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
- 3: This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
- 4: This step verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
- 8: This step tests for a short to voltage or an open.
- 10: If the A/C fuse is open be sure to test the A/C compressor clutch supply voltage circuit for a short to ground.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the A/C Relay ON and OFF in the ECM Special Functions, Engine Output Controls list. Does the A/C Relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
| 3 | Turn OFF the ignition. Disconnect the A/C compressor clutch relay. Turn ON the ignition, with the engine OFF. Probe the battery positive voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 4 | Go to Step 8 |
| 4 | Connect a test lamp between the control circuit of the A/C compressor clutch relay and the battery positive voltage circuit of the A/C compressor clutch relay. Start the engine. With a scan tool, command the A/C Relay ON and OFF. Does the test lamp turn ON and OFF with each command? | Go to Step 6 | Go to Step 5 |
| 5 | Test the control circuit of the A/C compressor clutch relay for a short to ground, short to voltage, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 7 |
| 6 | Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 7 | Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
| 8 | Repair the battery positive voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 11 | |
| 9 | Replace the A/C compressor clutch relay. Did you complete the replacement? | Go to Step 11 | |
| 10 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming. Did you complete the replacement? | Go to Step 11 | |
| 11 | Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. Does the DTC reset? | Go to Step 2 | System OK |
DTC P0645, P0646, or P0647
Symptoms - HVAC Systems - Automatic
| IMPORTANT | The following steps must be completed before using the symptom tables. |
- Perform the «Diagnostic System Check - Vehicle»(ref-197532-S30271296932005101200000) in Vehicle DTC Information, before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
- Review the system operation in order to familiarize yourself with the system functions. Refer to the following information: «Air Delivery Description and Operation»(ref-197560-S38109150332005101200000) «Air Temperature Description and Operation»(ref-197560-S42300243782005101200000)