GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Aurora 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 DTC P1540 Air Conditioning (A/C) Refrigerant Overpressure - Air Conditioning (A/C) Disabled

Object Number: 191650 Size: SF
Engine Controls Components
Cell 21: A/C Sensors
OBD II Symbol Description Notice
ESD Notice

Circuit Description

This diagnostic detects an over pressure condition in the A/C system. The DTC is set if the A/C high pressure switch, opens at 430 psi, disables the A/C clutch at least 10 times with high side temperature below a threshold. This is designed to detect blockages in the A/C system. When the DTC is set, the A/C clutch will be disabled for the ignition cycle.

Conditions for Running the DTC

A/C is ON.

Conditions for Setting the DTC

A/C clutch disabled 10 times by the A/C high pressure switch with the A/C high side temperature less than 87°C (109°F).

Action Taken When the DTC Sets

Disengage the A/C compressor for the ignition cycle.

    •  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 .

Diagnostic Aids

Use the Failure Rec. on the scan tool and note the conditions under which the DTC set. If A/C High Side Temp. was close to 87°C (189°F) then a high pressure condition probably occurred, if A/C High Side Temp. was low than an intermittent open circuit or switch probably set this DTC.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. Checking if fault is present.

    2.

  2. Checking if fault is pressure or switch / circuit problem.

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

  1. Turn the engine ON and the A/C ON.
  2. Using a scan tool observe the A/C Hi Press. Sw. display.

Does the display indicate Normal?

--

Fault not present. Refer to Diagnostic Aids

Go to Step 3

3

  1. Connect a manifold gauge set to A/C system.
  2. Turn the engine ON and the A/C ON.
  3. Monitor A/C high side pressure and A/C Hi Press. Sw. display.

When the scan tool display indicates Hi Press. is the A/C high side pressure above the value specified?

430 psi

Go to Step 7

Go to Step 4

4
  1. Turn the key to OFF.
  2. Disconnect the A/C high pressure switch and PCM connector C1.
  3. Check terminal contact at both the A/C high pressure switch and the PCM.
  4. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis

Go to Step 5

5
  1. Check CKT 451, CKT 604 and the ground for CKT 451 for an intermittent open condition.
  2. Repair if needed.

Was a repair made?

--

Go to Powertrain Control Module Diagnosis

Go to Step 6

6

Replace the A/C high pressure switch. Refer to Heating and Air Conditioning.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

--

7

Repair the cause of high A/C system pressure. Refer to Heating and Air Conditioning.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

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