Circuit Description
The air conditioning (A/C) compressor clutch relay is controlled by the engine control module (ECM). Ignition 1 voltage is supplied directly to the A/C compressor clutch relay. The ECM controls the relay by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volt. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit
Conditions for Running the DTC
| • | DTC P0606 is not set. |
| • | The A/C is requested. |
| • | The ignition 1 voltage is more than 11 volts. |
| • | DTC P0645 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects an improper voltage level on the A/C clutch relay control circuit for 10 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | For HVAC system concerns, refer to HVAC Preliminary Checks in Heating, Ventilation and Air Conditioning. |
| • | If condition is intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | |||||||||||
1 |
Important: This DTC will only set for a failure on the control side of the A/C clutch relay. Did you perform the Diagnostic System Check - HVAC Systems - Manual? | Go to Step 2 | |||||||||
2 |
Does the A/C Relay turn ON and OFF with each command? | Go to Step 3 | Go to Step 4 | ||||||||
3 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Diagnostic Aids | ||||||||
4 |
Does the test lamp illuminate? | Go to Step 5 | Go to Step 9 | ||||||||
5 |
Does the test lamp turn ON and OFF with each command? | Go to Step 10 | Go to Step 6 | ||||||||
6 | Does the test lamp remain illuminated with each command? | Go to Step 8 | Go to Step 7 | ||||||||
7 | Test the A/C clutch relay control circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | ||||||||
8 | Test the A/C clutch relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | ||||||||
9 |
Did you complete the repair? | Go to Step 14 | -- | ||||||||
10 | Test for an intermittent and for a poor connection at the A/C 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 14 | Go to Step 12 | ||||||||
11 | Test for an intermittent and for a poor connection at 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 14 | Go to Step 13 | ||||||||
12 | Replace the A/C clutch relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | Go to Step 14 | -- | ||||||||
13 | Replace the ECM. Refer to the appropriate procedure:
Did you complete the replacement? | Go to Step 14 | -- | ||||||||
14 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 15 | ||||||||
15 | Observe the capture info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |||||||||
