Torque Converter Diagnosis

Torque Converter Diagnosis





Prior to torque converter installation, all diagnostic procedures must be followed. This is to prevent the unnecessary installation of good torque converters. Only after a complete diagnostic evaluation can the decision be made to install a new torque converter.

Begin with the normal diagnostic procedures as follows:
1. Preliminary inspection.
2. Know and understand the customer's concern.
3. Verify the condition - carry out the torque converter operation test. Torque Converter Operation Test
4. Carry out diagnostic procedures. Diagnosis By Symptom
^ Carry out on-board diagnostics. Refer to Diagnostics.
- Repair all non-transmission related DTCs first.
- Repair all transmission-related DTCs.
- Rerun on-board diagnostics to verify repair.
^ Carry out Stall Speed Test. Refer to Special Testing Procedures. Stall Speed Test
^ Carry out Diagnostic Routines. Refer to Diagnosis By Symptom. Diagnosis By Symptom
- Use the Diagnosis by Symptom to locate the appropriate routine that best describes the symptom(s). The routine will list all possible components that may cause or contribute to the symptom. Check each component listed; diagnose and repair as required before changing the torque converter.

Torque Converter Operation Test
The Torque Converter Operation Test verifies that the torque converter clutch (TCC) control system and the torque converter are operating correctly.
1. Carry out Quick Test with scan tool. Refer to Computers and Control Systems. Check for DTCs.
2. Connect a scan tool to the vehicle.
3. Bring the engine to normal operating temperature by driving the vehicle at highway speeds for approximately 15 minutes in D position.
4. After normal operating temperature is reached, maintain a constant speed of about 56 km/h (35 mph) in 5th gear for 10 seconds.
5. Release the accelerator pedal and monitor the scan tool TP voltage to approximately 1.25 volts or 30% throttle.
6. Monitor the TCC and engine speed PID. The TCC should release and engine rpms should increase before the 5-4 shift occurs.

NOTE: The following is a list of common vehicle concerns that have been misdiagnosed as TCC shudder. For diagnosis of the following items, refer to Computers and Control Systems.

^ Spark plugs - check for cracks, high resistance or broken insulators
^ Plug wires
^ Fuel injector - filter may be plugged
^ Fuel contamination - engine driveability concerns
^ EGR valve - valve may let in too much exhaust gas and cause engine to run lean
^ Vacuum leak - engine will not get correct air/fuel mixture
^ Manifold absolute pressure (MAP)/mass air flow (MAF) sensor - incorrect air/fuel mixture
^ Heated oxygen sensor (HO2S) - too rich/lean air/fuel mixture
^ Fuel pressure - may be too low
^ Engine mounts - loose/damaged mounts can cause vibration concerns
^ Axle joints - check for vibration