ASE G1 Auto Maintenance and Light RepairAutomatic Transmission/TransaxleMedium
A technician is diagnosing an automatic transmission that shifts harshly and inconsistently, especially under heavy acceleration. The fluid level is correct and appears clean. A scan tool reveals no trouble codes. Which of the following components should the technician investigate next?
- AThe brake light switch.
- BThe throttle position sensor (TPS).
- CThe vehicle speed sensor (VSS).
- DThe transmission range sensor (TRS).
Show answer & explanationAnswer & explanation
Correct answer: B. The throttle position sensor (TPS).
Harsh and inconsistent shifting, particularly under heavy acceleration, often points to an issue with the throttle position sensor (TPS). The TPS provides critical input to the transmission control module (TCM) about engine load and driver demand. If this signal is inaccurate, the TCM may command incorrect shift points or pressures, leading to harsh shifts, even without setting a specific trouble code.
Why the other options are wrong
- A. A faulty brake light switch could affect torque converter lock-up or shift interlock, but generally not harsh, inconsistent shifts under acceleration.
- C. A faulty VSS usually causes erratic speedometer readings, incorrect shift points (e.g., too early/late), or torque converter issues, but less commonly harsh shifts specifically under acceleration.
- D. A faulty TRS typically causes incorrect gear display, no-start conditions, or inability to select certain gears, not harsh shifts under acceleration.
TPS & Harsh Shifting
An inaccurate or faulty Throttle Position Sensor (TPS) can cause an automatic transmission to shift harshly or inconsistently, as the Transmission Control Module (TCM) receives incorrect engine load data.
- TPS signals engine load to TCM.
- Incorrect signal leads to improper shift points/pressures.
- Often manifests under varying throttle input.
Memory trick: Harsh shifts, especially with throttle? TPS is the boss.