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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Wave 🢒 Engine 🢒 Engine Controls - 1.6L (L91) 🢒 DTC P0645

Circuit Description

The air conditioning (A/C) compressor clutch relay is controlled by the engine control module (ECM). Ignition 1 voltage is supplied directly to the A/C compressor clutch relay. The 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 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit

Conditions for Running the DTC
    • DTC P0606 is not set.
    • The A/C is requested.
    • The ignition 1 voltage is more than 11.0 volts.
    • DTC P0645 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects an improper voltage level on the A/C clutch relay control circuit for 10 seconds.

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 control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC
    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids
    • For HVAC system concerns, refer to HVAC Preliminary Checks in Heating, Ventilation, and Air Conditioning.
    • If condition is intermittent refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Important: This diagnostic trouble code (DTC) will only set for a failure on the control side of the A/C clutch relay.

Did you perform the Diagnostic System Check - HVAC Systems - Manual?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Manual

2

  1. Turn ON the ignition, with the engine OFF.
  2. Command the A/C Relay ON and OFF with a scan tool.

Does the A/C Relay turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the A/C clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit of the A/C clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 9

5

  1. Connect a test lamp between the control circuit of the A/C clutch relay and the ignition 1 voltage circuit of the A/C clutch relay.
  2. Start the engine.
  3. Command the A/C Relay ON and OFF with a scan tool.

Does the test lamp turn ON and OFF with each command?

Go to Step 10

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 A/C clutch relay control circuit for the following conditions:

    • An open
    • A high resistance
    • A short to voltage

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

8

Test the A/C clutch relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

9
  1. Repair the open or the short to ground in the ignition 1 voltage circuit of the A/C clutch relay. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuse as necessary.

Did you complete the repair?

Go to Step 14

--

10

Test for an intermittent and for a poor connection at the A/C 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 14

Go to Step 12

11

Test for an intermittent and for a poor connection at the engine control module (ECM). 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 14

Go to Step 13

12

Replace the A/C clutch relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 14

--

13

Replace the ECM. Refer to the appropriate procedure:

    •  Engine Control Module Replacement in Engine Controls - 1.2L.
    •  Engine Control Module Replacement in Engine Controls - 1.4L DOHC.
    •  Engine Control Module Replacement in Engine Controls - 1.4L SOHC.
    •  Engine Control Module Replacement in Engine Controls - 1.5L.
    •  Engine Control Module Replacement in Engine Controls - 1.6L (L91).

Did you complete the replacement?

Go to Step 14

--

14
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate he vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 15

15

Observe the capture info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK