XB50 - Check ACP VREF and ACP SIG RTN Circuits

Continuous Memory Diagnostic Trouble Code (DTC) 579 indicates the A/C Pressure (ACP) sensor did not detect a sufficient change in A/C system pressure when the A/C was turned on or the ACP circuit is above maximum voltage. This could be due to a problem in the ACP sensor circuits or the A/C system, and could be a hard fault or an intermittent concern.

Possible causes:
- Open or shorted ACP sensor circuit.
- A/C system mechanical concern.
- Damaged ACP sensor.
- Damaged Variable Control Relay Module (VCRM).
- Power-to-A/C clutch circuit open (DTC 586 also present).

NOTE: If Continuous Memory DTC 586 is also present, refer to the EEC-IV DTC charts to address the 586. Manufacturer Code Charts

- Key "OFF".

- Disconnect ACP sensor.

- Key "ON".

Air Conditioning Pressure Switch Connector:

- Measure voltage between the ACP VREF and the ACP SIG RTN circuits at the ACP sensor vehicle harness connector.

- Key "OFF".

- What was the voltage?

Greater than 6.0 volts -- Go to XB62 (to check ACP VREF for short to power). XB62 - Check ACP SIG RTN For Short to Power

Less than 4.0 volts -- Go to XB63 (to check ACP VREF and ACP SIG RTN circuits). XB63 - Check ACP SIG RTN and ACP VREF Circuit Continuity

Between 4.0 and 6.0 volts -- Go to XB51 (ACP VREF and ACP SIG RTN circuits OK to sensor). XB51 - Check If A/C Clutch Will Engage