For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The TCM uses the A/C Request signal in order to modify the shift program when the A/C is on. When the HVAC controls are in any position that enables the A/C compressor, the A/C Request circuit connects to B+. The TCM interprets this as a signal that the A/C compressor load is present.

### Diagnostic Aids

An intermittent may be caused by the following conditions:

• | Corrosion

• | Mis-routed harness

• | Rubbed through wire insulation

• | Broken wire inside the insulation

Refer to Symptoms for Intermittents.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. The scan tool should indicate Yes with the HVAC controls in any position that requests the A/C compressor.

2. The ECM and TCM A/C Request circuits connect within the HVAC control head. An open circuit will only affect that individual A/C Request circuit. A short to ground or B+ will affect both circuits.

#### A/C Request Circuit Diagnosis

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Transmission On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to On-Board Diagnostic System Check
2 |

1. Turn on the ignition with the engine off.
2. Turn the A/C on and off while observing the A/C Request on the scan tool.

Does the scan tool parameter toggle between Yes and No?

--

No trouble Found

Refer to the Diagnostic Aids

Go to Step 3

3 |

1. Turn off the ignition.
2. Disconnect the TCM.
3. Turn on the ignition with the engine off.
4. Connect the test light J 35616-200 between the A/C Request circuit in the TCM harness connector and ground.
5. Turn the A/C on and off while monitoring the test light.

Does the test light go on and off?

--

Go to Step 6

Go to Step 4

4 |

1. Turn off the ignition
2. Disconnect the ECM.
3. Turn on the ignition with the engine off.
4. Turn the A/C on and off while monitoring the test light.

Does the test light go on and off?

--

Go to Step 8

Go to Step 5

5 | Check both the ECM and the TCM A/C Request circuits for the following conditions and repair as necessary.

• | Open Circuit

• | Short to ground

• | Short to power

Was a problem found and corrected?

--

Go to Step 9

Go to Heater, Ventilation and Air Conditioning (HVAC)

6 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 9 | Go to Step 7
7 | Replace the TCM. Refer to TCM Replacement . Is the action complete? | -- | Go to Step 9 | --
8 | Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 9

--

9 |

1. Turn on the ignition with the engine off.
2. Turn the A/C on and off while observing A/C Request on the scan tool.

Does the scan tool parameter toggle between Yes and No?

--

System OK

Go to Step 3