Input/Turbine Speed Sensor "A" Circuit No Signal

What it means

The ECU is getting no signal at all from the input/turbine speed sensor. The input/turbine speed sensor measures how fast the transmission input shaft is spinning so the computer can control shifts and detect slipping.

Symptoms

• Check engine light on
• Harsh, delayed or erratic shifts
• Transmission stuck in one gear (limp mode)
• Speedometer problems on some vehicles

Probable causes

Most likely first

1. 1Damaged or unplugged connector
2. 2Open or shorted wiring
3. 3Failed sensor
4. 4Damaged reluctor (tone) ring

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Inspect the input/turbine speed sensor connector and wiring (on the transmission case). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
3. 3Watch the input/turbine speed sensor reading on live data. Input speed should closely follow engine RPM when the torque converter is locked.
4. 4Check the sensor resistance (for 2-wire sensors) or power and ground (for 3-wire Hall-effect sensors). Watch the signal on an oscilloscope or graphing meter while cranking or driving; it should be a clean, regular pattern.
5. 5If the wiring checks out, test the sensor itself against the specification in a service manual.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair the damaged wiring or connector
• Replace the input/turbine speed sensor
• Clear the code and test drive to confirm the repair