Torque Converter Cutaway 4R70W
Torque Converter Operation Test
This test verifies that the torque converter clutch control system and the torque converter are operating correctly.
1. Carry out Quick Test with scan tool. For additional information, refer to the Powertrain Control/Emissions Diagnosis manual (PCED). Check for DTCs.
2. Connect a tachometer to the engine.
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 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 five seconds after pedal is released. If this does not occur, see torque converter operation concerns.
6. If the vehicle stalls in (D) or manual 2 at idle with vehicle at a stop, move the transmission range selector lever to manual 1 position. If the vehicle stalls, see torque converter operation concerns.
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 torque converter clutch shudder. For diagnosis of the following items, refer to the appropriate sections of the workshop manual and the Powertrain Control/Emissions Diagnosis manual (PCED).
> Spark plugs - check for cracks, high resistance or broken insulators.
> Plug wires.
> Fuel injector - filter may be plugged.
> Fuel contamination - engine runs poorly.
> 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.
> MAP/MAF sensor - improper air/fuel mixture.
> HO2S sensor - 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.
Abbreviated Road Test Evaluation Form
If the shudder occurs a) during the 3-4 or 4-3 shift at HEAVY throttle, or b) at 40mph in 2, OD OFF, and OD, or c) at the same RPM in every gear, or d) coasting, cruising, or in R, or e) during extended light braking, then it is NOT TC clutch shudder.