Diagnostic Strategy

Diagnostic Strategy
Troubleshooting an electronically controlled automatic transmission is simplified by using the proven method of diagnosis. One of the most important things to remember is that there is a definite procedure to follow.

Air Conditioning (A/C) Clutch
An electromagnetic clutch is energized when the clutch cycling pressure switch closes. The switch is located on the suction accumulator/drier. The closing of the switch completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C clutch is engaged, Electronic Pressure Control (EPC) is adjusted by the PCM to compensate for additional load on the engine.

Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) sensor provides the Sequential Fuel Injection (SFI) system mixture temperature information. The IAT sensor is used both as a density corrector for air flow calculation and to proportion cold enrichment fuel flow. The IAT sensor is installed in the air cleaner outlet tube. The IAT sensor is also used in determining Electronic Pressure Control (EPC) pressures.

Engine Coolant Temperature (ECT) Sensor
The Engine Coolant Temperature (ECT) sensor detects temperature of engine coolant and supplies the information to the Powertrain Control Module (PCM). The ECT sensor is used to control Torque Converter Clutch (TCC) operation. The ECT is installed in the heater outlet fitting or cooling passage on the engine. For engine control applications, the ECT signal is used to modify ignition timing, EGR flow and air-to-fuel ratio as a function of engine coolant temperature.

Throttle Position (TP) Sensor
The Throttle Position (TP) sensor is a potentiometer mounted on the throttle body. The TP sensor detects the position of the throttle plate and sends this information to the Powertrain Control Module (PCM). The TP sensor is used for shift scheduling, electronic pressure control and Torque Converter Clutch (TCC) control.

NOTE: Do not take any short cuts or assume that critical checks or adjustments have already been made.

Follow the procedures as written to avoid missing critical components or steps.
To properly diagnose a concern have the following available:
- TSBs.
- Wiring Diagram. These provide the information required when diagnosing transmission concerns. Use the Diagnostic Flow Chart as a guide and follow the steps as indicated.

Preliminary Inspection
- Know and understand the customer's concern.
- Verify the concern by operating the vehicle.
- Check the fluid levels and condition.
- Check for non-factory add-on items.
- Check shift linkages for proper adjustment.
- Check TSBs regarding the concern.

Diagnostics
- Carry out on-board diagnostic procedures Key On Engine Off (KOEO) and Key On Engine Running (KOER).
- Record all Diagnostic Trouble Codes (DTCs).
- Repair all non-transmission codes first.
- Repair all transmission codes second.
- Erase all continuous codes and attempt to repeat them.
- Repair all continuous codes.
- If only pass codes are obtained, refer to Diagnosis By Symptom for further information and diagnosis. 4R70W

Follow the diagnostic sequence to diagnose and repair the concern the first time.