Circuit Description
Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (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 volts. 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 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0645 A/C Clutch Relay Control Circuit
Conditions for Running the DTC
| • | The ignition must be ON and the voltage must be between 9-18 volts. |
| • | The ECM driver is activated or deactivated. |
Conditions for Setting the DTC
| • | The ECM detects an improper voltage level on the output circuit that controls the A/C relay. |
| • | The condition is present for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The ECM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM will not store Freeze Frame or Failure Records. |
| • | The A/C compressor clutch is disabled for the ignition cycle. |
Conditions for Clearing the DTC
| • | The DTC will become history if the ECM no longer detects a failure. |
| • | The history DTC will clear after 40 fault-free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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.
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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.
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Verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
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Tests for a short to voltage or an open.
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If the A/C fuse is open ensure to test the A/C compressor clutch supply voltage circuit for 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 | |
Does the A/C Relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 8 | |
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 . 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 . 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 . Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
Repair the battery positive voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs . 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 | -- |
Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 11 | -- | |
11 |
Does the DTC reset? | Go to Step 2 | System OK |
