Input/Turbine Speed Sensor A Circuit Intermittent
The PCM detected an erratic or intermittent voltage signal from the input (turbine) speed sensor A circuit. This sensor monitors transmission input shaft speed, and an unstable signal prevents the transmission control module from accurately calculating shift points and gear ratios.
What You Might Notice
- Erratic or inaccurate speedometer readings
- Transmission fails to shift properly or shifts harshly
- Speedometer and/or odometer not functioning
- Check Engine Light illuminated
- Diminished fuel economy and delayed acceleration
Most Common Causes
- 1
Defective input speed sensor
The sensor itself has failed or is wearing out, causing intermittent electrical dropout or signal noise to the PCM.
- 2
Corroded or loose sensor connector
Moisture or corrosion on the sensor connector terminals creates intermittent electrical contact, producing erratic voltage signals.
- 3
Damaged wiring harness
A break, short, or pinch in the sensor wiring between the sensor and PCM interrupts signal transmission intermittently.
- 4
Engine control module (PCM) malfunction
A faulty PCM or corrupted software may misinterpret valid sensor signals as erratic, though this is less common than sensor failure.
How to Diagnose It
- 1
Check Defective input speed sensor — The sensor itself has failed or is wearing out, causing intermittent electrical dropout or signal noise to the PCM.
- 2
Check Corroded or loose sensor connector — Moisture or corrosion on the sensor connector terminals creates intermittent electrical contact, producing erratic voltage signals.
- 3
Check Damaged wiring harness — A break, short, or pinch in the sensor wiring between the sensor and PCM interrupts signal transmission intermittently.
- 4
Check Engine control module (PCM) malfunction — A faulty PCM or corrupted software may misinterpret valid sensor signals as erratic, though this is less common than sensor failure.
How to Fix It
- 1
Replace input speed sensor
Remove the defective sensor from the transmission housing and install a new OEM or quality replacement sensor with proper torque specification.
- 2
Inspect and repair connector
Disconnect the sensor connector and clean corroded terminals with electrical contact cleaner. Inspect for bent pins or damage; repair or replace the connector as needed.
- 3
Inspect and repair wiring harness
Visually trace the sensor wiring from the sensor to the PCM, checking for cracks, pinches, or exposed wire. Repair damaged sections with proper splicing or replace the entire harness if extensively damaged.
- 4
Clear code and test drive
After repairs, clear the diagnostic trouble code with a scanner and perform a test drive to verify transmission shift quality and speedometer accuracy. Recheck for code return.
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