BMW Cranks But Won’t Start
Your BMW cranks — the engine turns over — but it just won’t fire up. This can be frustrating and even confusing, especially if there were no warning signs. If your BMW cranks but doesn’t start, the problem is likely with fuel delivery, ignition, or a sensor that controls engine timing. In this guide, we’ll help you diagnose the issue step-by-step and get you closer to a solution.
What Does “Cranks But Won’t Start” Mean?
When you turn the key or push the start button, the starter motor engages, and the engine spins. That’s cranking. But if the engine doesn’t fire and run on its own, it means something critical — like fuel, spark, or compression — is missing.
This is different from a no-crank situation, where the engine doesn’t turn over at all. To better understand how BMW’s engine control systems work during startup, check out these BMW tech features and guides.
Common Reasons a BMW Cranks but Won’t Start
Here are the most common causes:
- Fuel delivery problem: Bad fuel pump, clogged fuel filter, or failed fuel injectors.
- No spark: Faulty ignition coils, crankshaft position sensor, or spark plugs.
- Crankshaft or camshaft sensor failure: The ECU can’t “see” the engine’s position to time spark/fuel correctly.
- Immobilizer (EWS/CAS) issue: The car’s anti-theft system may block ignition or fuel.
- Low compression: Usually caused by internal engine problems, though rare in healthy engines.
If you’re unsure how these systems interact, this BMW system overview is a great place to learn.
What to Check First
Before digging into complex systems, check the basics:
- Fuel: Is there fuel in the tank? Is the fuel pump priming (you should hear a hum for 2 seconds)?
- Battery voltage: Low voltage can affect spark and ECU function. A healthy battery should read 12.4–12.6V.
- Check engine light: Is it on? Scan for codes — even one stored code can point you in the right direction.
How to Diagnose the Issue
To identify what’s missing — fuel, spark, or sensor input — follow this process:
1. Check for Fuel
- Turn the key to “on” and listen near the rear seat for the fuel pump buzz.
- Use a fuel pressure gauge to test pressure at the rail.
- If no fuel pressure, suspect a faulty pump, relay, or clogged filter.
2. Check for Spark
- Remove a spark plug and check for spark by grounding it against metal while cranking.
- No spark usually means a bad coil, crankshaft sensor, or ignition module.
3. Check Crankshaft/Camshaft Sensors
- Scan with a BMW-specific OBD2 tool for codes like P0335 (crank sensor).
- If no signal is received, the engine won’t know when to inject or fire.
Learn how to use live data and diagnostic tools more effectively in these BMW diagnostics tutorials.
Symptoms That Help Pinpoint the Problem
| Symptom | Likely Issue |
|---|---|
| Cranks quickly, no fuel pump sound | Fuel pump, relay, or fuse issue |
| Cranks, fuel pressure present, no spark | Ignition coil or crank sensor problem |
| Cranks, then stalls immediately | Immobilizer (EWS/CAS) preventing engine operation |
| Cranks, but random misfires when attempting to start | Timing or sensor issue |
How Immobilizer (EWS or CAS) Can Stop Starting
BMW’s EWS (older models) or CAS (newer models) systems control whether the car allows the engine to start. If there’s a mismatch between the key and the module, the car will crank but cut fuel or spark.
Signs of immobilizer issues:
- Crank with no fire
- Security warning light or EWS error code
- Engine starts with a spare key but not the main one
These systems can be reset or reprogrammed using BMW diagnostic tools. Read more about BMW’s security systems and how they affect startup here.
Cost to Repair No-Start Issues
Here’s what you might expect to pay depending on the problem:
| Repair Type | Estimated Cost |
|---|---|
| Fuel pump replacement | $400 – $800 |
| Crankshaft or camshaft sensor | $200 – $400 |
| Ignition coil replacement | $100 – $250 per coil |
| EWS/CAS module sync or repair | $150 – $500 |
If you’re comfortable working on your car, some repairs like sensors and coils can be done DIY with simple tools.
When to Call a Mechanic
Call a BMW specialist if:
- You have fuel and spark but the engine still won’t start
- You’re getting EWS/CAS fault codes
- You’ve replaced parts but the issue remains
Some BMWs require dealer-level diagnostic tools to reset modules or read detailed data. If DIY methods don’t help, it’s time to get professional assistance.
Conclusion
If your BMW cranks but won’t start, the issue is likely fuel, spark, timing, or a sensor problem. Start with simple checks — fuel pressure, spark, and fault codes. Diagnosing the root cause early can save you time, money, and hassle.
Want to dig deeper into BMW engine management and startup systems? Explore our full library of BMW tech resources and troubleshooting guides.
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