What it means
Engine speed input from the ignition/distributor is in electrical range but plausibility check fails — slow response, drift, or noise.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The ignition or distributor engine-speed input reports engine rotation to the control module, which checks whether the signal follows engine speed plausibly. This code sets when the signal is present but responds, drifts, or varies outside the expected pattern, rather than disappearing completely.
Common causes
Most likely first.
- Sensor drift or pickup gap wrong
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check-engine light
- Engine may stall or hesitate
- Erratic tachometer reading
How to diagnose it
- Record freeze-frame data and compare live RPM with engine operation, watching for delayed, unstable, or implausible readings when the fault occurs.
- Inspect the pickup or speed-sensor mounting, connector, and wiring for looseness, contamination, damage, or movement.
- Check the sensor position or air gap only as specified for the vehicle, since an incorrect gap can distort an otherwise present signal.
- Test the speed-input waveform or signal through cranking and running using the manufacturer's procedure to distinguish sensor drift from wiring noise.
- If the sensor signal is sound at the sensor but not at the module, check the intervening harness and receiving circuit.
Common fixes
- Secure a loose pickup or sensor mounting and correct its position to the manufacturer's specification.
- Repair damaged wiring or a loose connector that is adding noise to the speed signal.
- Replace a sensor confirmed to drift or produce an unstable signal.
- Repair a confirmed fault in the receiving module or signal circuit.
Can I keep driving?
Because the engine may hesitate or stall as the speed signal becomes unreliable, avoid heavy traffic and high-speed trips if symptoms are occurring. A worsening signal can cause sudden loss of engine power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.