The differential clutch pump actuator check valve assembly is a pulse width modulated actuator mounted to the rear drive assembly. Ignition voltage is supplied to the clutch pump actuator check valve through a fused circuit. The powertrain control module (PCM) controls the actuator with a negative duty cycle. The actuator controls the supply fluid to the pump inlet in the rear drive assembly. When the actuator is commanded OFF, the PCM will detect a high voltage. When the actuator is commanded ON, the PCM will detect a low voltage. At engine start-up, the actuator is turned ON at 49-90 percent duty cycle for 3 seconds, then drops to 16-28 percent for holding. Every 30 seconds, the duty cycle is ramped to 49-90 percent for 0.5 second, then back to 16-28 percent. If the PCM detects a voltage on the axle actuator circuit that is outside of the calibrated limits then the all-wheel drive (AWD) disable lamp illuminates.

The AWD disable lamp illuminates when one of the following conditions exists for 5 seconds:

Schematic Reference

Differential Lock Schematics

Connector End View Reference

Rear Axle Connector End Views

Description and Operation

Differential Lock System Description and Operation

Electrical Information Reference

Scan Tool Reference

1. With a scan tool, verify the above data displays are within specification.

⇒	AWD temperature disables can be caused by an open circuit.

2. Using a scan tool, select the Body - Instrument Panel Cluster - Special Functions - Lamp Test mode.
3. In the Lamp Test mode you can turn on or off the instrument panel indicators. All indicators will turn ON when commanded on and OFF when commanded off. The AWD DISABLE indicator should turn on or off as commanded.

⇒	If the AWD DISABLE indicator is always ON or always OFF, replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.

All-Wheel Drive Disabled Indicator Malfunction

1. Ignition OFF, disconnect the C4 harness connector (Buick) or the C1 harness connector (Pontiac) at the I/P switch assembly.
2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, install a test lamp between the B+ circuit terminal C (Buick) or terminal D (Pontiac).
4. With a scan tool, command the IP display test ON and OFF. The test lamp should turn On and OFF when changing between the commanded states.

⇒	If the test lamp is always OFF, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always ON, test the B+ circuit for a short to voltage. If all circuits test normal, replace the BCM.

5. If all circuits test normal, replace the I/P switch assembly.

Differential Clutch Pump Actuator Check Valve Malfunction

1. Test the AWD Fuse in the Underhood Fuse Block. It should test NORMAL.

⇒	If the fuse is OPEN replace the fuse. If the fuse OPENs again check the AWD Ignition 1 Voltage circuit for a short to ground. If the circuit tests normal, replace the differential clutch pump actuator check valve.

2. Key ON, engine OFF. Disconnect the connector at the differential clutch pump actuator check valve. Measure the voltage between the AWD Ignition 1 Voltage circuit, clutch pump actuator check valve connector pin C, and a known good ground. The voltage should read B+.

⇒	If the voltage reads less than B+ repair the OPEN/HIGH RESISTANCE condition in the AWD Ignition 1 Voltage circuit.

3. Measure the voltage between the AWD Ignition 1 Voltage circuit, clutch pump actuator check valve connector pin C, and the AWD hard ground circuit, clutch pump actuator check valve connector pin B. The voltage should read B+.

⇒	If the voltage reads less than B+ repair the OPEN/HIGH RESISTANCE condition in the AWD hard ground circuit.

Important: The AWD Axle Actuator Control circuit is a modulated ground, with a duty cycle of 16-28 percent in the LOW range and 49-90 percent in the HI range. As such a test lamp will not work properly on it.

4. Measure the voltage between the AWD Ignition 1 Voltage circuit, clutch pump actuator check valve connector pin C, and the AWD Axle Actuator Control circuit, clutch pump actuator check valve connector pin A. The voltage should read B+.

⇒	If the voltage reads less than B+ test the AWD Axle Actuator Control circuit for an OPEN/HIGH RESISTANCE condition.

5. Key OFF. Measure the voltage between the AWD Ignition 1 Voltage circuit, clutch pump actuator check valve connector pin C, and the AWD Axle Actuator Control circuit, clutch pump actuator check valve connector pin A. The voltage should read 0 volts.

⇒	If the voltage reads greater than 0 volts test the AWD Axle Actuator Control circuit for a short to ground.

6. With the connector connected, connect a DMM in parallel to the control circuit. Set the DMM to read duty cycle.

Important: The differential clutch pump actuator check valve duty cycle will initiate at 49-90 percent duty cycle for 3 seconds, then drop to 16-28 percent duty cycle. Every 30 seconds, the duty cycle will cycle up to 49-90 percent for 0.5 seconds, then back to 16-28 percent.

7. Engine ON. Observe AWD Duty Cycle on the DMM from the time of engine start. Is the duty cycle functioning as described?

⇒	If the duty cycle differs from that described, replace the PCM.

8. If all circuits and connections test normal, replace the differential clutch pump actuator check valve.