What it means
Timing reference signal A pulses are erratic — connector or wiring intermittent, contamination on tone wheel, or sensor partially failed.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module monitors the timing pulses from signal A as the crankshaft turns. This code sets when those pulses become intermittent or erratic rather than remaining consistent, often because a connector loses contact under vibration, the sensor is failing, or the tone wheel is contaminated.
Common causes
Most likely first.
- Intermittent connector or contamination
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check engine light on
- Intermittent rough running or hesitation
- Stalling or hard starting
- Power loss
How to diagnose it
- Record freeze-frame data and review live engine-speed data to identify whether signal A becomes erratic during starting, idling, or a change in engine speed.
- Inspect signal A's connector for contamination, corrosion, loose terminals, or a latch that does not hold securely.
- Follow signal A's harness and look for chafing, strain, or contact with a vibrating, hot, or moving part.
- Inspect the tone wheel and sensor area for contamination, damage, or a mounting issue that could interrupt the signal.
- Monitor signal A's waveform while gently moving the harness and connector, then compare the result with the manufacturer's specification.
Common fixes
- Clean and secure the signal A connector and ensure its terminals make firm contact.
- Repair chafed wiring and secure the harness away from vibration or moving parts.
- Remove contamination from the tone-wheel or sensor area where accessible and appropriate.
- Replace the signal A sensor if its output remains intermittent with sound wiring and a clean target.
Can I keep driving?
Intermittent timing signal loss can cause hesitation or sudden stalling, so avoid driving if these symptoms occur. If the engine currently runs normally, keep any necessary trip short and stop if the fault returns.
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.