Engine Cranks But Won't Start When Warm
The engine cranks normally but fails to start when warm, indicating a likely fuel or sensor issue rather than a battery or starter problem. Common causes include a faulty crankshaft position sensor, fuel system issues, or vapor lock.
Diagnosis Details
Possible Causes
Faulty crankshaft position sensor (CPS) - fails when warm, causing no spark or injector pulse
Fuel pump or fuel pressure regulator issue - loss of residual pressure when hot
Vapor lock in fuel lines (less common on modern BMWs but possible in hot conditions)
Related OBD-II Codes
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What You Should Do
Check for spark and fuel pressure when warm.
Test crankshaft position sensor resistance and signal.
Scan for fault codes.
If no codes, monitor fuel pressure during hot restart attempt.
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Disclaimer: This AI-generated diagnosis is for informational reference only. Always consult a qualified mechanic for an in-person inspection. AutOwner is not responsible for decisions made based on this information.
