What it means
No pulses detected on timing reference signal A — open circuit, dead sensor, or air gap too wide.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The engine control module expects timing pulses from signal A while the crankshaft rotates. This code sets when it detects no pulses from that signal, so it cannot use signal A as expected; an open circuit, failed sensor, excessive sensor gap, or damaged tone wheel may be responsible.
Common causes
Most likely first.
- Failed timing reference sensor
- Open, damaged, or disconnected sensor wiring
- Excessive sensor-to-wheel gap or damaged tone wheel
Symptoms
- Check engine light on
- Engine may crank but not start
- Stalling or rough running
- Power loss
How to diagnose it
- Save freeze-frame data and check whether the scan tool shows engine speed while cranking, since no detected speed can support a missing timing signal.
- Inspect signal A's sensor connector for disconnection, corrosion, loose terminals, or physical damage.
- Trace signal A's wiring for an open, short, or damaged section, and test circuit continuity and connections using the vehicle wiring diagram.
- Check the sensor mounting and air gap against the manufacturer's specification, then inspect the tone wheel for damage.
- Test the sensor output during cranking against the manufacturer's specification before replacing the sensor.
Common fixes
- Reconnect or clean the signal A connector.
- Repair an open, shorted, or damaged section of signal A wiring.
- Correct excessive sensor gap or mounting problems to the manufacturer's specification.
- Replace the signal A sensor or repair the damaged tone wheel if testing confirms the fault.
Can I keep driving?
The engine may crank without starting or may stall, so do not rely on the vehicle for a journey. If it stalls in traffic or cannot restart, arrange recovery; repeated cranking can drain the battery.
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.