Torque Converter Lock-Up Clutch (TCC) Diagnosis

Torque Converter Lock-Up Clutch (TCC) Diagnosis
To properly diagnosis the lock-up clutch (TCC) system, perform all electrical testing first and then 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
Inspect
1. Install a tachometer or scan tool.
2. Operate the vehicle unit proper operating temperature is reached.
3. Drive the vehicle at 80 to 88 km/h (50 to 55 mph) with light throttle (road load).
4. Maintaining throttle position, lightly touch the brake pedal and check for release of the TCC and a slight increase in engine speed (rpm).
5. Release the brake slowly accelerate and check for a reapply of the Lock up clutch and a slight decrease in engine speed (rpm).

Torque Converter Evaluation
Torque Converter Stator
The torque converter stator roller clutch can have one of two different type malfunctions:
A. Stator assembly freewheels in both directions.
B. Stator assembly remains Locked up at all times.
^ Condition A - Poor Acceleration Low Speed
The car tends to have poor acceleration from a stand still. At speeds above 50 to 55 km/h (30 to 35 mph), the car may act normal. If poor acceleration is noted, it should first be determined that the exhaust system is not blocked, and the transaxle is in 1st (First) gear when starting out.
If the engine freely accelerates to high rpm in N (Neutral), it can be assumed that the engine and exhaust system are normal. Checking for poor performance in "Drive" and "Reverse" will help determine if the stator is freewheeling at all times.
^ Condition B- Poor Acceleration High Speed
Engine rpm and car speed limited or restricted at high speeds. Performance when accelerating from a standstill is normal. Engine may overheat. Visual examination of the converter may reveal a blue color from overheating.
If the converter has been removed, the stator roller clutch can be checked by inserting two fingers into the splined inner race of the roller clutch and trying to turn freely clockwise, but not turn or be very difficult to turn counter clockwise.

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 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 make sure the noise is actually coming from the converter:
1. Place foot on brake.
2. Put gear selector in "Drive".
3. Depress accelerator to approximately 1200 rpm for no more than six seconds.

CAUTION: If the accelerator is depressed for more than six seconds, damage to the transaxle may occur.

A torque converter noise will increase under this load.

CAUTION: This noise should not be confused with pump whine noise which is usually noticeable in P (Park), N (Neutral) and all other gear ranges. Pump whine will vary with pressure ranges.

The torque converter should be replaced under any of the following conditions:
^ External leaks in the hub weld area.
^ Converter hub is scored or damaged.
^ Converter pilot is broken, damaged or fits poorly into crankshaft.
^ Steel particles are found after flushing the cooler and cooler lines.
^ Pump is damaged or steel particles are found in the converter.
^ Vehicle has TCC shudder and/or no TCC apply. Replace only after all hydraulic and electrical diagnoses have been made.(Lock up clutch material may be glazed.)
^ Converter has an imbalance which cannot be corrected .
^ Converter is contaminated with engine coolant containing antifreeze.
^ Internal failure of stator roller clutch.
^ Excess end play.
^ Heavy clutch debris due to overheating (blue converter).
^ Steel particles or clutch lining material found in fluid filter or on magnet when no internal parts in unit are worn or damaged (indicates that lining material came from converter).

The torque converter should not be replace if:
^ The oil has an odor, is discolored, and there is no evidence of metal or clutch facing particles.
^ The threads in one or more of the converter bolt holes are damaged. -correct with thread insert.
^ Transaxle failure did not display evidence of damage or worn internal parts, steel particles or clutch plate lining material in unit and inside the fluid filter.
^ Vehicle has been exposed to high mileage (only). The exception may be where the Lock up clutch damper plate lining has seen excess wear by vehicles operated in heavy and/or constant traffic, such as taxi, delivery or police use.

Lock-Up Clutch Shudder Diagnosis
The key to diagnosing lock-up clutch (TCC) shudder is to note when it happens and under what conditions.
TCC shudder should only occur during the APPLY and/or RELEASE of the Lock up clutch.

While TCC Is Applying or Releasing
If the shudder occurs while TCC is applying, the problem can be within the transaxle or torque converter.
Something is not allowing the clutch to become fully engaged, not allowing clutch to release, or is trying to release and apply the clutch at the same time. This could be caused by leaking turbine shaft seals, a restricted release orifice, a distorted clutch or housing surface due to long converter bolts, or defective friction material on the TCC plate.

Shudder Occurs after TCC Has Applied:
In this case, most of the time there is nothing wrong with the transaxle! As mentioned above, once the TCC has been applied, it is very unlikely that will slip. Engine problems may go unnoticed under light throttle and load, but become noticeable after TCC apply when going up a hill or accelerating, due to the mechanical coupling between engine and transaxle.

CAUTION: Once TCC is applied there is no torque converter assistance. Engine or driveling vibrations could be unnoticeable before TCC engagement.

Inspect the following components to avoid misdiagnosis of TCC shudder and possibly disassembling a transaxle and/or replacing a torque converter unnecessarily:
^ Spark plugs - Inspect for cracks, high resistance or broken insulator.
^ Plug wires - Lock in each end, if there is red dust (ozone) or black substance (carbon) present, then the wires are bad. Also look for a white discoloration of the wire indicating arcing during hard acceleration.
^ Distributor cap and rotor - look for broken or un-crimped parts.
^ Coil - look for black on bottom indication arcing while engine is misfiring.
^ Fuel injector - filter may be plugged.
^ Vacuum leak - engine won't get correct amount of fuel. May run rich or lean depending on where the leak is.
^ EGR valve - valve may let it too much unburnable exhaust gas and cause engine to run lean. MAP sensor - like vacuum leak, engine won't get correct amount of fuel for proper engine operation.
^ Carbon on intake valves - restricts proper flow or air/fuel mixture into cylinders.
^ Flat cam - valves don't open enough to let proper fuel/air mixture into cylinders.
^ Oxygen sensor - may command engine too rich or too lean for too long.
^ Fuel pressure - may be too low.
^ Engine mounts - vibration of mounts can be multiplied by TCC engagement.
^ Axle joints - checks for vibration.
^ TPS - TCC apply and release depends on the TPS in many engines. If TPS is out of specification, TCC may remain applied during initial engine starting.
^ Cylinder balance - bad piston rings or poorly sealing valves can cause low power in a cylinder.
^ Fuel contamination - causes poor engine performance.