Crankshaft Position Sensor "A" Circuit

What it means

The engine computer (ECU) has detected an electrical problem in the crankshaft position (CKP) sensor circuit. The crankshaft position (CKP) sensor tells the ECU the crankshaft speed and position, which it needs to fire the spark plugs and injectors. The signal is missing or outside the range the ECU will accept.

Symptoms

• Check engine light on
• Engine cranks but will not start
• Stalling, often when the engine is hot
• Misfires or stumbling
• Tachometer dropping to zero while driving

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 crankshaft position (CKP) sensor connector and wiring (near the crankshaft pulley, on the bellhousing near the flywheel, or on the engine block). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
3. 3Watch the crankshaft position (CKP) sensor reading on live data. Engine RPM should appear on the scan tool while cranking. If RPM reads zero while cranking, the ECU is not seeing the crank signal.
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 crankshaft position (CKP) sensor
• Clear the code and test drive to confirm the repair