DTC P1546. Buick Regal 2002

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2002 🢒 Regal 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC P1546

DTC P1546 L36, L67

Circuit Description

Battery positive voltage is supplied to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through 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 PCM. When the PCM is commanding a component on, the voltage of the control circuit should be near 0 volts. When the PCM 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 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.

Conditions for Running the DTC

•	The ignition voltage is between 9.0-18.0 volts.

•	The ignition is ON.

Conditions for Setting the DTC

•	A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.

•	The condition is present for at least 30 seconds.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

•

The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.

•	A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.

•	A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using a scan tool.

Diagnostic Aids

If condition not present refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

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.

Tests for voltage at the coil side of the A/C compressor clutch relay.

Verifies that the PCM is providing ground to the A/C compressor clutch relay.

Tests if ground is constantly being applied to the A/C compressor clutch relay.

Tests for a short to voltage or an open.

Perform the recalibration procedure for the PCM.

Step	Action	Yes	No
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views
1	Did you perform the HVAC Diagnostic System Check?	Go to Step 2	Go to Diagnostic System Check - HVAC Systems - Manual
2	Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the A/C Relay ON and OFF in the Special Functions, Engine Output Controls list. Does the A/C Compressor clutch relay turn ON and OFF with each command?	Go to Diagnostic Aids	Go to Step 3
3	Turn OFF the ignition. Disconnect the A/C compressor clutch relay. Turn ON the ignition, with the engine OFF. Probe the battery positive voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground. Does the test lamp illuminate?	Go to Step 4	Go to Step 10
4	Connect a test lamp between the A/C compressor clutch relay control circuit of the A/C compressor clutch relay and the battery positive voltage circuit of the A/C compressor clutch relay. With a scan tool, command the A/C Relay ON and OFF . Does the test lamp turn ON and OFF with each command?	Go to Step 8	Go to Step 5
5	Does the test lamp remain illuminated with each command?	Go to Step 7	Go to Step 6
6	Test the A/C compressor clutch relay control circuit of the A/C compressor clutch relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 9
7	Test the A/C compressor clutch relay control circuit of the A/C compressor clutch relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 9
8	Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 11
9	Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 13	Go to Step 12
10	Repair the battery positive voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?	Go to Step 13	--
11	Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement?	Go to Step 13	--
12	Important: Perform the programming procedure for the PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement?	Go to Step 13	--
13	Use the scan tool in order to clear the DTCs . Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. Does the DTC reset?	Go to Step 2	System OK

DTC P1546 LG8