Circuit Description
Ignition voltage is supplied directly to the A/C compressor clutch relay. The 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 PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the 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 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 PCM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0645 Air Conditioning A/C Clutch Relay Control Circuit
Conditions for Running the DTC
| • | The ignition voltage is between 9.0-18.0 volts. |
| • | The engine speed is more than 80 RPM. |
| • | The PCM driver transitions from ON to OFF or from OFF to ON. |
Conditions for Setting the DTC
The PCM detects an open on the control circuit of the A/C compressor clutch relay.
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 A/C compressor clutch is disabled. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Failure Records. |
| • | The driver information center, if equipped may display a message. |
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 PCM engine grounds are secure and clean.
If DTC P0645 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.
-
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.
-
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.
-
Verifies that the powertrain control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
-
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 | ||||||
|---|---|---|---|---|---|---|---|---|---|
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 | ||||||
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 | |||||||
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 the following:
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 powertrain control module (PCM). 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 | ||||||
Repair the coil side 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 | -- | ||||||
Replace the PCM. Refer to Control Module References in Computer/Integrating Systems 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 | ||||||
