A passive speed sensor signal depends on movement and its installation. A waveform that becomes clearer at higher speed does not automatically clear the sensor circuit of a starting fault.
Interpreting the evidence
Record the signal during the actual failed start and compare it with cranking speed, supply condition and the specified sensor arrangement. Connector resistance, sensor clearance and the target wheel need consideration alongside the sensor itself. The useful question is what the ECU receives at the difficult operating point.
Keep this evidence
Include cranking speed, whether the engine starts when warm, and a capture from the failed attempt.
Use the vehicle’s signal requirements. An attractive waveform at idle cannot establish that the low-speed starting signal is adequate.
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Technical background from HELLA. The referenced design explains the principle; the vehicle-specific procedure determines the repair.
Related reading — Hall and inductive crank sensors need different test methods. Browse all vehicle-electronics diagnostic notes or return to the repair library.