ASE G1 Auto Maintenance and Light RepairAutomatic Transmission/TransaxleMedium
A customer reports that their automatic transmission sometimes 'hangs' in a gear, staying at high RPM for too long before eventually shifting harshly. This occurs intermittently. The fluid level and condition are good, and no DTCs are present. Which of the following is the most likely cause?
- AThe governor pressure sensor is failing.
- BA restricted vacuum modulator line.
- CThe transmission control module (TCM) is receiving an incorrect throttle position sensor (TPS) signal.
- DAn internal clutch pack is sticking.
Show answer & explanationAnswer & explanation
Correct answer: C. The transmission control module (TCM) is receiving an incorrect throttle position sensor (TPS) signal.
The throttle position sensor (TPS) tells the TCM how much power the driver is demanding. If the TCM receives an intermittently high TPS signal, it will delay upshifts and increase line pressure, leading to the symptom of 'hanging' in gear at high RPM and then shifting harshly, even if the driver is only lightly accelerating.
Why the other options are wrong
- A. Governor pressure sensors are found in older, hydraulically controlled transmissions; modern electronic transmissions use solenoids and other sensors for pressure control.
- B. A restricted vacuum modulator line (found in older transmissions) would typically cause consistently early and soft shifts, not hanging at high RPM then harsh shifts.
- D. A sticking clutch pack would likely cause slipping or delayed engagement, not typically 'hanging' at high RPM before a harsh shift.
Throttle Position Sensor (TPS)
The Throttle Position Sensor (TPS) measures the throttle plate's angle, providing the engine/transmission control module with information about driver acceleration demand.
- Crucial for shift timing and firmness.
- Signal directly influences line pressure and shift points.
- A faulty TPS can cause erratic shifting or performance issues.
Memory trick: Speed and Load dictate the gear change code.