For 1990-2009 cars

For schematic details, refer to

#### A/C System

Engine Controls Components
Powertrain Control Module Controlled Air Conditioning Description
Engine Cooling Fans
Automatic Transmission, Park/Neutral Position Switch
OBD II Symbol Description Notice
Ignition Switch and Underhood Electrical Center 2
U/H Center 2: ETC and A/C Cruise Fuses
Information Sensors
G112 V8 VIN G
Powertrain Control Module Connector End Views
.

### Circuit Description

The A/C system uses an A/C refrigerant pressure sensor mounted in the high side of the A/C system to monitor A/C refrigerant pressure. The PCM utilizes this information in order to disable the A/C compressor clutch when the A/C system pressure is out of range. The PCM also uses A/C refrigerant pressure sensor to enable the engine coolant fans when the A/C refrigerant pressure is high.

The PCM supplies a 5 volt reference, a signal circuit, and a ground circuit to the A/C refrigerant pressure sensor. As the A/C pressure increases or decreases, the resistance of the sensor changes and varies the amount of signal voltage detected by the PCM.

### Diagnostic Aids

Important:

• | Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM.

• | For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

• | The following may cause an intermittent:

- | Poor connections; Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

- | Mis-routed harness.

- | Rubbed through wire insulation.

- | Broken wire inside the insulation.

• | If the test did not fail this ignition cycle, move the related electrical harnesses and the connectors while monitoring a scan tool.

• | For an intermittent, refer to Symptoms .

### Test Description

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

1. The normal A/C voltage is between 1.0 and 1.8 volts.

2. If the A/C pressure/voltage stays high after disconnecting the A/C refrigerant pressure sensor electrical connector, this indicates the signal circuit is shorted to a voltage.

3. This step tests for a good ground circuit.

4. This step verifies the integrity of the A/C refrigerant pressure sensor signal circuit.

5. If you have thoroughly inspected the 5.0 volt reference circuit (for opens, shorts to ground, PCM connections etc.) and is OK, then replace the PCM.

6. If you have thoroughly inspected the ground circuit for opens and the PCM connections are OK, then replace the PCM.

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. Install the scan tool.
2. Idle the engine.
3. Monitor the DTC Information using the scan tool.

Did DTC P1639 fail this ignition cycle?

--

Go to DTC P1639 5 Volt Reference 2 Circuit

Go to Step 3

3 |

1. Turn ON the ignition leaving the engine OFF.
2. Monitor the A/C High Side parameter using the scan tool.

Does the scan tool indicate the A/C High Side Pressure voltage within the specified range?

0.1-1.8V

Go to Step 4

Go to Step 5

4 | Move related harnesses while monitoring the A/C High Pressure voltage. Does the scan tool indicate that the sensor values change while moving related electrical harnesses? | -- | Go to Step 16 | Go to Diagnostic Aids
5 | Disconnect the A/C refrigerant pressure sensor electrical connector. Refer to

#### Right Rear Side of the Engine Compartment

(1) | A/C Refrigerant Pressure Sensor
(2) | Right Shock Tower
(3) | Engine Wiring Harness

in HVAC Systems with A/C-Manual or Automatic.

Does the scan tool indicate the A/C High Side less than the specified value?

1V

Go to Step 6

Go to Step 10

6

Measure the voltage from the A/C refrigerant pressure sensor 5 volt reference circuit to the battery ground using the DMM J 39200 .

Is the voltage near the specified value?

5V

Go to Step 7

Go to Step 11

7

Measure the voltage from the A/C refrigerant pressure sensor 5 volt reference circuit to the sensor ground circuit using the DMM J 39200 .

Is the voltage at the specified value?

5V

Go to Step 8

Go to Step 12

8

Jumper the 5 volt reference circuit to the A/C refrigerant pressure sensor signal circuit using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.

Does the scan tool indicate the A/C High Side voltage at the specified value?

5V

Go to Step 9

Go to Step 13

9

Repair the faulty A/C refrigerant pressure sensor connection or faulty sensor. Refer to A/C Refrigerant Pressure Sensor Replacement in HVAC Systems with A/C-Manual or Automatic.

Is the action complete?

--

System OK

--

10

Repair the short to voltage in the A/C refrigerant pressure sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

11

Repair the A/C refrigerant pressure sensor 5 volt reference circuit . Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 14

12

Repair the A/C refrigerant pressure sensor ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 14

13

Repair the A/C refrigerant pressure sensor signal circuit . Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 14

14

1. Inspect for a poor sensor ground terminal connection at the PCM connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a condition, repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Is the action complete?

--

System OK

Go to Step 15

15

Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the action complete?

--

System OK

--

16

1. Inspect for a poor sensor connection or PCM connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a condition, repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Is the action complete?

--

System OK

--