With Out Transmission Test Box

Chart C-8A, Torque Converter Clutch (TCC) Functional Check:

Transaxle Control Circuit Diagram:

CIRCUIT DESCRIPTION:
The purpose of the Torque Converter Clutch feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of the automatic and the fuel economy of a manual transaxle. Two PCM controlled solenoids, located inside the transaxle, regulate fluid pressure to the torque converter clutch. One solenoid (the TCC solenoid) provides fluid pressure to the TCC, the other solenoid (the Pulse Width Modulated or PWM solenoid), regulates pressure for a smooth apply.

The solenoids get battery power when the ignition is turned "ON", and become energized when the PCM completes the circuit to ground. When the TCC solenoid coil is activated ("ON,") fluid pressure applies the torque converter clutch, making a straight mechanical coupling between the engine and transmission. When the TCC solenoid is deactivated, fluid pressure to the TCC is released and the torque converter clutch disengages, allowing the torque converter to operate in the conventional manner (fluid coupling between engine and transaxle).

The TCC brake switch is connected in-line with the power supply to the TCC solenoid and is used to interrupt power to the solenoid when the brake is applied. The PCM monitors voltage in the power supply circuit after the brake switch, at the TCC brake input terminal (BA5). Low voltage at this terminal (zero or near zero) indicates the brakes are being applied. The PCM then disables TCC and PWM solenoid operation until conditions for apply are again present.

TCC will engage when the following conditions are present:
^ Engine warmed up.
^ Vehicle speed above a calibrated value (about 28 mph 45 km/h).
^ Throttle position sensor output not changing, indicating a steady road speed.
^ Brake switch closed.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Determines whether the fault is caused by a bad solenoid or control circuit.
2. Checks availability of B+ on circuit 420.
3. Checks the PCM's ability to pulse the PWM solenoid "ON" and "OFF".
4. Electrical circuits have checked out. If there is a TCC engagement problem, it would be a mechanical or hydraulic problem in the transmission.

DIAGNOSTIC AIDS:
The "Scan" tool only indicates when the PCM has turned "ON" the TCC driver and this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, road test the vehicle. Engine rpm should decrease when the "Scan" indicates the TCC driver has turned "ON."