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 concern
3. Verify the condition- carry out the Torque Converter Operation Test
4. Carry out diagnostic procedures
- Carry out On-Board Diagnostic (OBD) ; refer to Diagnostics. Diagnostics
- Repair all non-transmission related DTCs first.
- Repair all transmission DTCs.
- Rerun OBD (On-Board Diagnostic) to verify repair.
- Carry out Line Pressure Test. Refer to Special Testing Procedures Special Testing Procedures.
- Carry out Stall Speed Test. Refer to Special Testing Procedures Special Testing Procedures.
- Carry out Diagnostic Routines. Refer to Diagnosis By Symptom Diagnosis By Symptom.
- Use the Diagnosis by Symptom Index 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
NOTE: Always drive the vehicle in a safe manner according to the driving conditions and obey all traffic laws.
The torque converter operation test verifies that the Torque Converter Clutch (TCC) control system and the torque converter are operating correctly.
1. Carry out Self Test with scan tool. Refer to Computers and Control Systems Information. Check for DTCs.
2. Connect a scan tool.
3. Bring the engine to normal operating temperature by driving the vehicle at highway speeds in (D) position.
4. After normal operating temperature is reached, maintain a constant vehicle speed of about 80 km/h (50 mph) and tap brake pedal with the left foot.
5. Engine rpm should increase when brake pedal is tapped, and decrease about 5 seconds after pedal is released. If this does not occur, see torque converter operation concerns. Refer to Diagnosis By Symptom Diagnosis By Symptom.
6. If the vehicle stalls in (D) or manual 2 at idle with vehicle at a stop, move the selector lever to manual 1 position. If the vehicle stalls, see torque converter operation concerns. Refer to Diagnosis By Symptom Diagnosis By Symptom. If the vehicle does not stall in (D), refer to Diagnosis By Symptom Diagnosis By Symptom.
7. If the vehicle exhibits a vibration during the road test, complete the Road Test Evaluation Form. This form will aid the technician in determining the source of the vibration.
NOTE: The following is a list of common vehicle concerns that have been misdiagnosed as TCC (Torque Converter Clutch) shudder. For diagnosis of the following items, refer to the appropriate systems of the diagnostic/repair information and Computers and Control Systems Information.
- Spark plugs- check for cracks, high resistance or broken insulators
- Ignition coil-on-plug- short or open circuit
- 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) and 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
