No ignition but speed pulses present
* Investigate if the vehicle has been under environmental disturbances like vibrations etc * Check motion sensor operation and the cable harness – replace sensor if found faulty * Check for evidence of tampering * Check if speed pulses are being injected through front connector.
What you'll see
No driver-visible symptom recorded.
System reaction
MC33/EV408: * Message with error text: "v-impulses w/o ignition" together with Memory Code 33 is shown in the tachograph display. * Event is not stored in the tachograph memory.
Diagnostic depth
Pulses from the motion sensor when ignition is switched off.
This is a known problem and can occur when the edge of a cog lies in front of the motion sensor, and the vehicle is parked but slightly moving. This “phenomenon” can happened due to strong wind and transport by a ferry etc. Other possibilities are: * Fault in the cable harness * Fault in the motion sensor * The vehicle have been towed