Input/Turbine Speed Sensor A Circuit No Signal
The PCM detected no voltage signal from the input (turbine) speed sensor circuit A. This 3-wire electromagnetic sensor monitors transmission input shaft speed, and without its signal, the transmission cannot properly control shift timing or the vehicle cannot determine speed accurately.
What You Might Notice
- Erratic or non-functioning speedometer and odometer
- Transmission unable to shift gears or shifts harshly
- Intermittent speedometer operation
- Loss of vehicle speed information to other systems
- Possible limp mode or reduced transmission performance
Most Common Causes
- 1
Open or shorted wiring harness
Broken, corroded, or disconnected wires in the sensor circuit prevent voltage signal transmission to the PCM. Inspect the entire wiring harness from sensor to connector for damage or corrosion.
- 2
Faulty input/turbine speed sensor
The sensor itself has failed internally or its coil has opened, eliminating signal generation. The sensor may be worn out or damaged from transmission fluid contamination.
- 3
Loose or corroded connector
Poor contact at the sensor connector or PCM connector prevents voltage flow. Moisture intrusion or oxidation can degrade the connection quality significantly.
- 4
PCM or wiring fuse failure
A blown fuse in the sensor circuit or internal PCM damage can eliminate power to the sensor circuit entirely. Check the appropriate fuse box for blown fuses related to transmission controls.
How to Diagnose It
- 1
Check Open or shorted wiring harness — Broken, corroded, or disconnected wires in the sensor circuit prevent voltage signal transmission to the PCM. Inspect the entire wiring harness from sensor to connector for damage or corrosion.
- 2
Check Faulty input/turbine speed sensor — The sensor itself has failed internally or its coil has opened, eliminating signal generation. The sensor may be worn out or damaged from transmission fluid contamination.
- 3
Check Loose or corroded connector — Poor contact at the sensor connector or PCM connector prevents voltage flow. Moisture intrusion or oxidation can degrade the connection quality significantly.
- 4
Check PCM or wiring fuse failure — A blown fuse in the sensor circuit or internal PCM damage can eliminate power to the sensor circuit entirely. Check the appropriate fuse box for blown fuses related to transmission controls.
How to Fix It
- 1
Inspect and repair wiring harness
Visually trace the entire wiring harness from the input speed sensor to the PCM connector. Look for broken insulation, corrosion, pinched wires, or loose connections. Repair or replace damaged sections and ensure all connectors are clean and firmly seated.
- 2
Test and replace input speed sensor
Use a multimeter to test for voltage and resistance at the sensor. If no voltage is present with ignition on, or resistance values are infinite (open circuit), replace the sensor. Ensure proper installation depth and torque specifications.
- 3
Clean and reconnect sensor connectors
Disconnect both the sensor and PCM connectors. Clean terminals with electrical contact cleaner and a soft brush to remove corrosion. Dry thoroughly and reconnect firmly until you hear or feel a click. Apply dielectric grease to connector terminals.
- 4
Check transmission fuse and PCM power supply
Locate the fuse box (refer to vehicle manual) and check the transmission control or input speed sensor fuse. If blown, replace with the correct amperage rating. If fuse blows again, suspect PCM wiring or internal PCM failure requiring professional service.
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