HVAC System - Manual

DTC P1545

Circuit Description

Ignition voltage is supplied directly to the air conditioning (A/C) compressor clutch relay. The powertrain control module (PCM) or engine control module (ECM) controls the relay by grounding the A/C clutch relay 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. The driver has a fault line which is monitored by the PCM or ECM. When the PCM or ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the PCM or 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 will set.

The PCM or ECM will monitor the control circuit for the following:

* A short to ground
* A short to voltage
* An open circuit
* An open relay coil
* An internally shorted or excessively low resistance relay coil

When the PCM or ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1545 Air Conditioning A/C Clutch Relay Control Circuit

Conditions for Running the DTC

* The ignition voltage is between 9.0-18.0 volts.
* The engine speed is more than 80 RPM.
* The PCM or ECM driver transitions from ON to OFF or from OFF to ON.

Conditions for Setting the DTC

The PCM or ECM detects an open on the control circuit of the A/C compressor clutch relay.

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 A/C compressor clutch is disabled.
* The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Failure Records.
* The driver information center, if equipped may display a message.

Conditions for Clearing the DTC

* A last test failed, or current DTC clears when the diagnostic runs and passes.
* The DTC can be cleared by using a scan tool.

Diagnostic Aids

Important: Be sure to verify that the PCM or ECM engine grounds are secure and clean.

If DTC P1545 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids. Component Tests and General Diagnostics

Test Description

Step 1 - Step 11:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
3. Tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
4. Verifies that the powertrain control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
8. Tests for a short to voltage or an open.
10. If the A/C fuse is open ensure to test the A/C compressor clutch supply voltage circuit for short to ground.