A failing crankshaft position sensor is one of the most common root causes when a BMW refuses to start. The check covers three parameters: signal quality, resistance, and the air gap to the pulse wheel. The telltale scenario: the engine starts confidently cold, then won’t start at all once warm.
Vehicle Identification
The diagnosis is tied to one specific car: you enter the 17-digit VIN (Fahrgestellnummer). Processing runs locally in your browser — the number isn’t stored and isn’t shared with third parties.
Common Symptoms
- No-start.
- Stumbling (misfires) on a warm engine.
- The engine stalls.
The key quirk: the symptoms often show up only on a warm engine. With the engine cold, measurements frequently fall within spec — which throws you off during a first check.
Fault Codes
| Code | As Attributed in the Source Data |
|---|---|
| 2A82 | listed as a possible code for a faulty crankshaft sensor |
| 29F1 | listed in the same set of possible codes |
| P1343 | appears in cross-references and the knowledge graph as the crankshaft signal code |
| 2C72 | O2 sensor B1S1 signal |
| P2015 | swirl flap sensor (Drallklappen) |
A contradiction in the source. The sensor’s diagnostic page names only 2A82 and 29F1 as possible codes, while the knowledge graph and cross-references treat P1343 as the crankshaft signal code. The source offers no clean one-code-one-fault mapping. In practice, check both sets: first the codes logged in the control unit’s memory, then the knowledge-graph interpretation.
Most Likely Cause
At operating temperature the sensor goes high-resistance or loses its signal entirely — the classic hot-restart problem. The control unit stops receiving a valid crankshaft position and blocks the start.
That explains the engine’s behavior: cold, the part measures within spec; heat changes its resistance and signal quality, and the engine stalls or won’t start. Testing it cold returns a false negative.
Diagnostic Procedure
- Measure the sensor’s resistance cold and at operating temperature. The manufacturer’s spec is 800–1200 Ω. Compare the two readings to each other, not just against the spec sheet.
- Capture the signal with an oscilloscope during a cranking attempt. Judge the shape and stability of the pulses, not just whether pulses are there.
- Inspect the air gap to the pulse wheel (Luftspalt zum Impulsrad).
What to Check Before Replacing the Sensor or Control Unit
Before swapping any component, check the power supply, ground, and wiring integrity (a continuity test of the circuit). This step is mandatory, not a formality: it rules out faults a new part won’t fix.
Tools
- Fluke 115 multimeter — voltage and resistance measurement plus circuit continuity checks on sensors, connectors, and wiring.
- Oscilloscope — capturing the signal during a cranking attempt.
- BGS 723 LED test light (3–48 V) — checking voltage at fuses, connectors, and ground connections without loading sensitive control units.
- ISTA — BMW’s factory diagnostic software; without it, the crankshaft position adaptation can’t be performed.
Repair
The job goes in this order: replace the sensor, replace the O-ring seal, then run the crankshaft position adaptation through ISTA. The source specifically calls for an OEM Bosch sensor — that’s a direct instruction from the source, not generic brand advice.
Replace the O-ring along with the sensor: reusing the old seal invites a leak and a second teardown.
When You Need a Shop
If you don’t have BMW diagnostic software (ISTA), take the car to a BMW specialist. Without the factory software you can’t run the crankshaft position adaptation, and without it the repair stays incomplete.
What Shops See in Practice
Per the source’s observations, the culprit is very often the wiring harness or a connector rather than the component itself. That’s why the sequence “electrics first, part second” saves time and rules out replacing good parts. The source offers no failure statistics by mileage — the takeaway is limited to that observation.
Related Content
The “common problems” blocks, the knowledge graph, and the automated collections all repeated one another — they’re consolidated into a single list below.
- Fault codes: P1343 (crankshaft signal), P2015 (swirl flap sensor), 2C72 (O2 sensor B1S1).
- Engines: N47, B47, B57.
- Symptoms: BMW won’t start; BMW cranks and immediately stalls; Check Engine light on; power loss; heater stays cold; vibrations — at idle, usually engine mounts or misfires; at 62–75 mph, typically tires, wheel balance, or the driveshaft; under braking, warped brake rotors.
- Checks: camshaft sensor (cross-checked against the crank signal), fuel supply, fuel rail pressure, coolant leaks, turbocharger.
- Components: Valvetronic, high-pressure fuel pump (HDP/HPFP), water pump, thermostat, valve cover gasket, turbocharger, injectors (piezo and solenoid).
- Models: 3 Series E90, 3 Series E91, 5 Series F10.
The Bottom Line
A no-start on a warm engine with normal cold operation is reason enough to start with the crankshaft position sensor. The order of operations: measure resistance in both temperature states (800–1200 Ω per the spec), capture the oscilloscope signal during a cranking attempt, inspect the pulse wheel air gap. Only after verifying power, ground, and wiring do you replace the sensor — with a new O-ring and the adaptation run through ISTA.