Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM)/powertrain control module (PCM) controls the relay by grounding the A/C clutch relay 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. The driver has a fault line which is monitored by the ECM/PCM. When the ECM/PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM/PCM 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.
The ECM/PCM will monitor the control circuit for the following:
• | A short to ground |
• | A short to voltage |
• | An open circuit |
• | An open relay coil |
• | An internally shorted or excessively low resistance relay coil |
When the ECM/PCM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.
This diagnostic procedure supports the following DTCs:
• | DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit |
• | DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage |
• | DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage |
• | The ignition voltage is between 9-18 volts. |
• | The engine speed is more than 80 RPM. |
• | The ECM/PCM driver transitions from ON to OFF or from OFF to ON. |
The ECM/PCM detects an open on the control circuit of the A/C compressor clutch relay.
The ECM/PCM detects a short to ground on the control circuit of the A/C compressor clutch relay.
The ECM/PCM detects a short to voltage on the control circuit of the A/C compressor clutch relay.
• | The ECM/PCM will not illuminate the malfunction indicator lamp (MIL). |
• | The ECM/PCM 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. |
• | 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. |
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 .
The numbers below refer to the step numbers on the diagnostic table.
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.
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.
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.
This step tests for a short to voltage or an open.
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 |
---|---|---|---|
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 ECM/PCM. 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/PCM. 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 |