P1545

Circuit Description
The A/C Request Circuit - When the HVAC controls are in any position that enables the A/C compressor, and the A/C compressor refrigerant switch is closed (low and high), the A/C request circuit is connected to B+. The ECM energizes the A/C compressor control circuit when a high signal voltage is detected on the A/C request circuit. The ECM will de-energize the A/C compressor control circuit during the WOT maneuvers, when the ECT exceeds a predetermined threshold or when the A/C request circuit signal voltage goes low (either by a pressure switch opening, or the HVAC system is in a non-A/C mode).

The A/C Load Signal - The ECM also receives an input on the A/C load signal circuit. This is accomplished through a pressure switch connected to B+ which is normally open. When the refrigerant high side pressure reaches approximately 1,200 kPa, the switch closes sending a B+ signal to the ECM. The ECM will then raise the idle speed by approximately 50 RPM in order to help compensate for these conditions.

The A/C Compressor Control Circuit - The ignition voltage is supplied directly to the A/C compressor control relay coil. The ECM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. When the ECM is commanding a component on, the voltage of the control circuit should be low (near 0 volts). When the ECM is commanding the control circuit to a component off, the voltage potential of the circuit should be high (near battery voltage).

The relay controls the high current flow to the A/C compressor clutch. This allows the ECM driver only to have to handle the relatively low current used by the relay.

Conditions for Running the DTC
^ The battery voltage is between 7.5 - 15 volts.
^ The vehicle engine speed is more than 65 km/h (40 mph).
^ The A/C clutch has been requested.

Conditions for Setting the DTC
ECM internal circuitry determines there is an open or a short in the A/C compressor relay control circuit.

Action Taken When the DTC Sets
The ECM will not illuminate the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC
^ The DTC clears after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other non-emission related diagnostic.
^ The ECM battery voltage is interrupted.
^ The scan tool clears the MIL/DTC.

Diagnostic Aids

Notice: Refer to J 35616-A Connector Test Adapter Kit Notice in Service Precautions.

Use the J 35616-A connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector.

Check for the following conditions:
^ Poor connections at the ECM or at the component-Inspect the harness connectors for a poor terminal to wire connection.
^ Damaged harness-Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help locate the fault.

Refer to Symptoms for the Intermittents. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. Listen for an audible click when the relay operates. Repeat the commands as necessary.
3. This check can detect a partially shorted coil which would cause an excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm, the coil may open (amps drop to 0), or short (goes above 0.20 amp).
15. Perform the Idle Learn Procedure when replacing the ECM or the throttle body.