smartcarofamerica.com/threads/smart-fortwo-451-wont-crank-until-whirring-noise-stops-crankshaft-position-sensor.159516/

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Source: smartcarofamerica.com

smartcarofamerica.com/threads/smart-fortwo-451-wont-crank-until-whirring-noise-stops-crankshaft-position-sensor.159516/ · p. 1 · Applies to: 451

Forum thread: Smart Fortwo 451 won't crank until whirring noise stops (crankshaft position sensor) | Smart Car of America Forum Source: smartcarofamerica.com Topic: crankshaft position sensor Models discussed: 451 Solution status: yes

Problem: 2007 Smart Fortwo 451 won't crank for 1+ minutes after ignition switch on; a whirring noise must stop before the engine will start. The issue reoccurs each time the ignition is switched off for a few minutes.

Solution: The problem was a crankshaft position sensor with a drifting leak between output and ground. This caused the startup diagnostic routine to stall during fuel pump priming, making the fuel pump (the whirring noise) run excessively long. Replacing the crankshaft position sensor resolved the issue. The sensor costs approximately £40 ($50), is accessible without a ramp (mounted underneath the engine at the back), and is secured by a single bolt and snap connector.

Key facts: - Symptom: extended fuel pump whirring noise on startup, delaying engine crank by 1+ minutes; noise stops on its own after several minutes, then engine cranks normally - Root cause: crankshaft position sensor with drifting leak between output and ground pin - Diagnostic note: OBD fault code was recorded but disappeared once noise stopped, initially misleading troubleshooting; ELM adapter did not clearly highlight the problem - Fix verified: replacing crankshaft position sensor eliminated startup delay; startup diagnostic routine now completes unhindered - Sensor location: underneath engine at rear, single bolt fastening, snap-on connector; no ramp needed for access - Cost: £40 (~$50); some vendors sell as sets with camshaft position sensor