Intermediate Shaft Speed Sensor A Circuit Intermittent
The Powertrain Control Module (PCM) has detected an erratic, intermittent, or missing signal from the transmission's intermediate shaft speed sensor 'A'. The computer sets this code when the sensor's rotational speed data drops out or fluctuates outside of expected parameters, preventing accurate shift timing.
An intermittent speed sensor signal can cause erratic shifting, transmission slipping, or force the vehicle into limp mode. It should be diagnosed promptly to prevent potential internal transmission damage and unsafe driving conditions.
Common symptoms
- Illuminated Check Engine Light
- Harsh or erratic transmission shifting
- Transmission slipping between gears
- Vehicle stuck in limp mode (failsafe mode)
- Erratic or malfunctioning speedometer
Likely causes
- Damaged, loose, or corroded wiring and connectors in the sensor circuit
- Contaminated transmission fluid or metal debris on the sensor's magnetic tip
- Faulty intermediate shaft speed sensor
- Internal transmission mechanical failure
- Faulty Powertrain Control Module (PCM) or Transmission Control Module (TCM)
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Fluid that is very dark, smells burnt, or contains excessive metal shavings indicates internal wear that could contaminate the sensor.
Visually inspect the sensor's wiring harness and connector.
Look for: Look for chafed wires, melted insulation, or corroded pins that could cause an intermittent electrical connection.
Remove the intermediate shaft speed sensor and inspect its tip.
Look for: Check for a buildup of metallic debris on the magnetic tip of the sensor, which can distort or block the signal.
Test the sensor's internal resistance using a digital multimeter.
Look for: Compare the measured resistance to the manufacturer's specifications; an out-of-range or fluctuating reading indicates a failing sensor.
Monitor the sensor's live data using an advanced scan tool or oscilloscope.
Look for: Look for dropouts, spikes, or an erratic waveform in the speed signal while the vehicle is in motion or the wheels are turning.
This page explains the generic P0794 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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