P1538

DTC P1537 or P1538

Circuit Description

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

DTC Descriptor

This diagnostic procedure supports the following DTCs:

* DTC P1537 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage

* DTC P1538 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage

Conditions for Running the DTC

* The engine is running.

* The ignition 1 voltage is more than 11.0 volts.

* The A/C is requested ON.

* The A/C compressor is running (P1537 only)

* The DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects a low voltage on the A/C clutch relay control circuit for more than 25 seconds.

OR

The ECM detects a high voltage on the A/C clutch relay control circuit for more than 25 seconds.

Action Taken When the DTC Sets

* The malfunction indicator lamp (MIL) will not illuminate.

* The ECM will store conditions which were present when the DTC was set as Failure Records data only.

* This information will not be stored in the Freeze Frame data.

Conditions for Clearing the MIL/DTC

* DTCs can be cleared by using the scan tool.

* Disconnect the ECM battery feed for more than 10 seconds.

Diagnostic Aids

* For HVAC system concerns, refer to HVAC Preliminary Checks HVAC Preliminary Checks in Heating, Ventilation, and Air Conditioning.

* If condition is intermittent refer to Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

* The following table illustrates the A/C compressor relay terminal locations in the underhood fuse block:






2.

Listen for a click when the A/C compressor relay operates. When the relay is commanded On with the scan tool, the ECM pulses the relay ON and OFF several times. Repeat the command as necessary.