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 control circuit through 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 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0645 Air Conditioning Clutch Relay Control Circuit
Conditions for Running the DTC
| • | The ignition voltage is between 9-18 volts. |
| • | The PCM driver is activated for at least 0.5 seconds. |
Conditions for Setting the DTC
The PCM detects an improper voltage level on the output circuit that controls the A/C relay.
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM stores the failure records. |
| • | The A/C compressor clutch is disabled. |
Conditions for Clearing the DTC
| • | The DTC will become history if the PCM no longer detects a failure. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared with a scan tool. |
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 | |
2 |
Important: The ambient air temperature must be above 3°C (38°F).
Does the A/C compressor operate? | Go to Step 3 | |
3 |
Does the A/C Relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 4 |
4 |
Does the test lamp illuminate? | Go to Step 5 | Go to Step 11 |
5 |
Does the test lamp turn ON and OFF with each command? | Go to Step 9 | 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 control circuit of the A/C compressor clutch relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
8 | Test the control circuit of the A/C compressor clutch relay for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
9 | 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 14 | Go to Step 12 |
10 | 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 . Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
11 | Repair the ignition 3 voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 14 | -- |
12 | Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement . Did you complete the replacement? | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 14 | -- |
14 |
Does the DTC reset? | Go to Step 2 | System OK |
