P0645

DTC P0645 A/C Clutch Output Circuit Fault

Circuit Diagram:

Circuit Description
When the engine control module (ECM) detects that A/C has been requested, the ECM will activate the A/C clutch relay. When the relay has been activated, voltage should be present at both the A/C compressor clutch and the A/C clutch status circuit at the ECM.

Conditions for Setting the DTC
- DTC P1650 not set.
- Ignition ON and voltage is greater than 11 volts.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will not illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after four consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
Check for the following conditions:
- Poor connection at the ECM. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
- Damaged harness. Inspect the wiring harness for damage. If the harness appears OK, observe the throttle position display on the scan tool while moving connectors and wiring harnesses related to the Throttle Position (TP) sensor. A change in the display will indicate the location of the fault.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. A problem that may prevent the compressor from engaging may or may not cause DTC P0645 to set.
3. If the scan tool indicates that the A/C request is ON, then the status circuit is OK.
4. Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (rpm, load, vehicle speed, temperature, etc.) that were noted. This will isolate when the DTC failed.
5. Checks whether ignition voltage is available at the relay.
6. Determines if the A/C relay is at fault or the A/C request circuit is at fault. If the A/C clutch engages, this indicates that the A/C status circuit is OK.
10. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.

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