3.2.201. SPN 4201, FMI 2, Crank speed signal erratic, too much noise pulses¶
Description
The crankshaft speed and angular position evaluation module expects a defined sequence of pulses from the crankshaft speed sensor (a trigger wheel with 58 teeth and a gap 2 teeth wide). If too many pulses are received between the two gaps, the system reports a fault.
Possible causes are:
- An invalid signal from the crankshaft sensor.
- The sensor wiring is defective.
- The sensor is defective.
- The distance between the sensor and the trigger wheel is too high, possibly a loose sensor.
- An external electromagnetic disturbance is affecting the sensor signal.
- The trigger wheel is defective.
Reaction in EEM
The FC is stored and the warning lamp is activated. The CAN message indicates active fault. Engine power will be reduced (Degradation Level 2). The engine starting may take longer than normally, and the running may be poor due to missing/incorrect information for the injection timing control. The engine runs with the camshaft speed sensor signal.
Solution
First save the error log and then erase it. Restart the ECU after erasing the error log. If the fault occurs again during the next driving cycle, check the following paths:
- Check the crankshaft sensor wiring, the connectors and the contact surfaces of the connector pins (possible oxidation). Look also for a possible reverse connection.
- Check the coil resistance of the crankshaft sensor (the engine must be stopped). The normal resistance values are + 20°C is 1120 - 1530 Ohms.
- Check the crankshaft sensor mounting. The air gap between the sensor tip and the trigger wheel teeth should be 0,2 - 1,0 mm.
- Look for possible electromagnetic noise sources on or close to the vehicle, disturbing the speed sensor signal (devices using or carrying high currents, high voltages or strong magnetic fields).
- Check the condition and the mounting of the crankshaft trigger wheel (damaged teeth, the positioning of the trigger wheel).
See Crankshaft speed sensor for reference.