3T40 Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

Circuit Description with 3T40 Automatic Transmission
The torque converter clutch solenoid valve (TCC solenoid valve) receives power from the fuse panel on circuit 439. The normally-open 3rd clutch pressure switch interrupts the ground path from the TCC solenoid valve. The Powertrain Control Module (PCM) activates the TCC solenoid valve by grounding the circuit through an internal switch in the PCM. Although the PCM commands the TCC solenoid valve On, the converter clutch does not apply until the 3rd clutch oil (3rd clutch engaged) closes the pressure switch, completing the circuit. Activating the TCC solenoid valve blocks exhaust fluid. This moves the converter clutch control valve to the applied position, and provides fluid pressure to engage the torque converter clutch.

When the PCM detects low TCC slip and the torque converter clutch is commanded off, then DTC P0742 sets. DTC P0742 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ No TP sensor DTC P0121, P0122 or P0123.
^ The PCM has commanded the TCC off.
^ The engine speed is 1,500-4,000 RPM.
^ Engine torque is greater than 13 N.m (10 lb ft).
^ Time since the last gear selector lever change has been more than 6 seconds.
^ The speed ratio is 0.9-1.375.
^ The throttle angle is greater than 8 percent.
^ The slip speed is -20 to +20 RPM for 10 seconds.
^ The vehicle speed is 56-120 km/h (35-75 mph).

CONDITIONS FOR SETTING THE DTC
The PCM detects two or more counts of the TCC being stuck on.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the conditions for setting the DTC are met.
^ The PCM stores DTC P0742 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns off the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool can clear the MIL/DTC.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission-related diagnostic fault occurring.

DIAGNOSTIC AIDS
^ If the vehicle stalls repeatedly, the TCC is mechanically stuck on.
^ Inspect the connectors at the PCM, AT inline harness connector and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step determines whether the stuck on condition is due to an electrical condition or a mechanical condition.
3. This step tests for a short to ground on the TCC circuit (CKT 422) solenoid valve control between the automatic transmission wiring harness and the PCM.