Torque Converter Clutch Circuit Check - LT. Truck: Notes

Fig 1: TCC Circuit Diagram (Lt. Truck)

Courtesy of GENERAL MOTORS CORP.

The automatic transmission TCC eliminates power loss of torque converter stage when vehicle is in a cruise condition. This allows the convenience of the automatic transmission, and fuel economy of a manual transmission.

Fused battery ignition is supplied to the TCC solenoid, located inside valve body, to shift a spool valve in order to modulate pressure to the TCC.

The PCM/TCM will engage TCC by grounding circuit No. 422 to energize the solenoid.

TCC will engage under the following conditions:

• Vehicle speed is greater than 30 MPH (48 km/h).
• Engine at normal operating temperature greater than 149°F (65°C).
• Transmission at normal operating temperature of 195°F 91°C).
• Throttle position sensor output is not changing, indicating a steady road speed.
• Brake switch is closed.
• 4th gear is indicated.
• No codes are stored.
  NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. This step checks for a shorted internal transmission harness or TCC solenoid .
  2. This step verifies power supply to the TCC solenoid.
  3. This step checks circuit No. 422 for a short to ground.
  4. This step checks PCM/TCM s ability to control the TCC solenoid. If bidirectional Scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.