DTC P1538 Air Conditioning (A/C) Request Circuit High Voltage. Oldsmobile Aurora 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Aurora 🢒 DTC 🢒 DTC P1538 Air Conditioning (A/C) Request Circuit High Voltage

Engine Controls Components
OBD II Symbol Description Notice
ESD Notice
ESD Notice

Circuit Description

This diagnostic test indicates if the A/C request circuit is shorted to voltage. This is done by comparing the A/C Request line (CKT 603) to the serial data received from the HVAC controller. If A/C is not requested by serial data and the A/C Request line (CKT 603 ) is high, voltage present, then DTC P1538 is set.

Conditions for Running the DTC

•	DTC P1605 not set.

•	A/C compressor not requested by the HVAC programmer via serial data.

Conditions for Setting the DTC

A/C request line high continuously for 20 seconds.

Action Taken When the DTC Sets

Disable the A/C compressor.

•	The Malfunction Indicator Lamp (MIL) will not illuminate.

•	No message will be displayed.

Conditions for Clearing the DTC

•	A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.

•	A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

•	Use a scan tool to clear DTCs.

•	Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in Powertrain Control Module Description .

Step	Action	Value(s)	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Start and idle the engine. Turn the HVAC A/C controls to OFF. Using a scan tool observe the DTC information Fail This Ign. Wait one minute. Has this DTC set?	--	Go to Step 3	Fault not present. Refer to Diagnostic Aids
3	Using a scan tool observe the A/C Request display. Does A/C Request display Yes?	--	Go to Step 4	Go to Step 10
4	Disconnect A/C low pressure switch connector. Observe the A/C Request display. Does A/C Request display Yes?	--	Go to Step 6	Go to Step 5
5	Reconnect A/C low pressure switch connector. Remove HVAC cont fuse. Observe the A/C Request display. Does A/C Request display Yes?	--	Go to Step 7	Go to Step 9
6	Record the fluid life indexes, turn the key to OFF and wait 30 seconds. Disconnect PCM connector C1. Turn the key ON. Using DMM J 39200 measure the voltage to ground at PCM connector C1 terminal 76. Is the voltage more than the value specified?	0.5 V	Go to Step 8	Go to Step 10
7	Repair the short to voltage on CKT 762. Is the repair complete?	--	Go to Powertrain Control Module Diagnosis	--
8	Repair the short to voltage on CKT 603. Is the repair complete?	--	Go to Powertrain Control Module Diagnosis	--
9	Replace the HVAC programmer. Refer to Heating and Air Conditioning. Is the replacement complete?	--	Go to Powertrain Control Module Diagnosis for Verify Repair	--
10	Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the replacement complete?	--	Go to Powertrain Control Module Diagnosis	--