To properly diagnosis the torque converter clutch (TCC) system, first perform all electrical testing, then perform the hydraulic testing.
The TCC is applied by fluid pressure which is controlled by a solenoid located inside the valve body. The solenoid is energized by completing an electrical circuit through a combination of switches and sensors.
Functional Check Procedure
- Install a tachometer or a scan tool.
- Operate the vehicle until proper operating temperature is reached.
- Drive the vehicle at 80-88 km/h (50-55 mph) with light throttle.
- Maintain the throttle position while you lightly touch the brake pedal and verify the release of the TCC and a slight increase in engine speed.
- Release the brake slowly, accelerate, and verify a reapply of the TCC with a slight decrease in engine speed.
Torque Converter Evaluation
The roller clutch on the torque converter stator can malfunction in 2 different ways:
Condition A - Poor Acceleration at Low Speed
The stator assembly freewheels in both directions.
The vehicle tends to have poor acceleration from a standstill. At speeds greater than 50-55 km/h (30-35 mph), the vehicle may act normal. If poor acceleration is noted, verify that the transaxle is in First gear when starting
out, and determine that the exhaust system is not blocked.
If the engine freely accelerates to high RPM in Neutral, assume that the engine and the exhaust system are normal. Testing for poor performance in Drive and Reverse will help to determine if the stator is freewheeling at all times.
Condition B - Poor Acceleration at High Speed
The stator assembly remains locked up at all times.
Engine RPM and car acceleration may be limited or restricted at high speeds, even though performance is normal while accelerating from a standstill. The engine may overheat. Visually examine the converter for a blue color caused by overheating.
If the converter has been removed, inspect the stator roller clutch by inserting 2 fingers into the splined inner race of the roller clutch. If the stator is locked up, you will be able to turn the clutch freely in a clockwise direction, but cannot
easily turn the clutch in a counterclockwise direction.
Noise
Torque converter whine is usually noticed when the vehicle is stopped and the transaxle is in Drive or Reverse. The noise will increase when the engine RPM is increased. The noise will stop when the vehicle is moving or when the torque converter clutch
is applied because both halves of the converter are turning at the same speed.
Perform a stall test to verify that the noise is actually coming from the converter;
- Place your foot on the brake.
- Put the gear selector is Drive. A torque converter noise will increase under this load.
Caution: You may damage the transmission if you depress the accelerator for more than 6 seconds.
- Depress the accelerator to approximately 1200 RPM for no more than 6 seconds.
Note: Do not confuse this noise with pump whine which is noticeable in all gear ranges. Pump whine varies with pressure ranges.
Replace the torque converter under any of the following conditions:
| • | External leaks occur in the hub weld area. |
| • | The converter hub is scored or damaged. |
| • | The converter pilot is broken, damaged, or fits poorly into the crankshaft. |
| • | Steel particles are found after flushing the cooler and the cooler lines. |
| • | The pump is damaged or steel particles are found in the converter. |
| • | The vehicle has TCC shudder or no TCC apply. Replace the converter only after all hydraulic and electrical diagnoses have been made. TCC material may be glazed. |
| • | The converter has an imbalance which cannot be corrected. |
| • | The converter is contaminated with engine coolant containing antifreeze. |
| • | The stator roller clutch has failed internally. |
| • | You observe excess end play. |
| • | You notice heavy clutch debris due to overheating. |
| • | You find steel particles or clutch lining material in the fluid filter or on a magnet when no internal parts in the unit are worn or damaged. This indicates that the lining material came from the converter. |
Replacement of the converter is not necessary under any of the following conditions:
| • | The oil has an odor or is discolored, and you can find no evidence of metal or clutch facing particles. |
| • | The threads in one or more of the converter bolt holes are damaged. Correct this condition with a thread insert. |
| • | The transaxle failure did not display evidence of damaged or worn internal parts, steel particles, or clutch plate lining material in the unit or inside the fluid filter. |
| • | The vehicle odometer indicates high mileage. The exception to this condition occurs when the TCC damper plate lining is excessively worn in vehicles which are operated in heavy , constant traffic, such as taxi, delivery, or police usage. |
