Your BMW cranks but won’t start? You’re not alone. This is one of the most common and confusing issues BMW owners face. The starter turns the engine, but the car simply refuses to fire up. In this guide, we’ll break down exactly what causes a crank-no-start condition and walk you through a systematic troubleshooting process to identify and fix the problem.
What Does “Crank No Start” Mean?
In a “crank no start” condition, your engine spins when you turn the key or push the start button, but it doesn’t ignite or run. That means your starter motor works, but something critical—like spark, fuel, or compression—is missing.
3 Core Requirements for Engine Start
Your BMW needs the following to start:
- Fuel: Adequate fuel pressure and injector operation
- Air: Proper airflow and sensor readings
- Spark: Ignition timing and coil performance
If even one of these is missing, your car will crank without starting.
Step-by-Step BMW Crank No Start Diagnosis
1. Scan for Trouble Codes First
Start with an OBD-II scanner—preferably BMW-compatible (Foxwell NT510, Carly, ISTA).
- Check for codes like P0335 (Crankshaft Position Sensor), P0340 (Camshaft Sensor), P0230 (Fuel Pump Circuit), or EWS/CAS immobilizer faults
Tip: Even if your check engine light isn’t on, codes may still be stored.
2. Check Fuel Delivery
Fuel issues are a leading cause of crank-no-start scenarios. Here’s what to test:
- Turn the key to “ON” and listen for fuel pump priming near rear seat
- Use a fuel pressure gauge at the fuel rail (normal range: 50–70 PSI)
- Check fuel pump relay and fuse in fuse box
Fix: Replace fuel pump, relay, or fuel filter if pressure is low or zero.
3. Inspect Crankshaft and Camshaft Position Sensors
These sensors tell the ECU when to fire the spark plugs and inject fuel. If either one fails, the ECU won’t trigger ignition.
- No RPM reading while cranking = bad crankshaft sensor
- Codes like P0335 or P0340 = sensor failure
Fix: Replace sensor using OEM parts only. Aftermarket versions may cause inconsistent starting.
4. Check for Spark
Remove a spark plug and ignition coil. Ground the plug against the engine and have someone crank the engine. You should see a strong spark.
- No spark = ignition coil, crank sensor, or DME issue
- Weak or intermittent spark = check power supply and grounds
Fix: Replace bad coil packs or spark plugs. BMWs like the N52, N54, and B58 have known coil issues.
5. Test the Immobilizer (EWS or CAS System)
If the ECU doesn’t recognize the key, it will block spark and fuel even if the engine cranks.
- Look for immobilizer light flashing or messages like “Key not recognized”
- Try a spare key if available
- Scan for EWS or CAS codes using a BMW diagnostic tool
Fix: Resynchronize or replace EWS/CAS module and reprogram keys if needed.
6. Verify Airflow and MAF Sensor Operation
While not a common cause of complete no-start, a failed MAF can cause the engine to stall shortly after starting or misfire on startup.
- Disconnect the MAF sensor and try starting the car
- If the engine starts, the MAF is likely faulty
Fix: Replace the MAF sensor or check for intake leaks.
7. Confirm Engine Compression (Rare but Possible)
If all else checks out, test engine compression. This is rare, but timing chain failure or valve issues can result in low/no compression.
- Use a compression tester on all cylinders
- Readings should be above 120 PSI
Fix: Low compression may require major engine repair or rebuild.
Common BMW Models and Crank No Start Patterns
| Model | Common Cause |
|---|---|
| BMW E46 (325i, 330i) | Crankshaft sensor, fuel pump relay |
| BMW E90 (2006–2011) | Fuel pump, coil failure, CAS module |
| BMW F30 (2012–2018) | Timing chain stretch (N20), key not detected |
| BMW X5/X3 | Battery voltage, fuel pump, EWS/CAS faults |
Common Diagnostic Tools
- Foxwell NT510: BMW-specific scanning and real-time data
- BMW ISTA (INPA): Dealer-level software
- Multimeter: For voltage and continuity tests
- Fuel pressure gauge: To test delivery
- Spark tester: To confirm ignition spark
When to Call a Mechanic
If you’ve done the basic checks and the engine still cranks without starting, call a specialist if:
- Fuel pressure and spark are both present, but the engine still won’t start
- There are EWS/CAS or DME (ECU) communication errors
- You don’t have access to BMW coding or programming tools
Average Repair Costs
| Repair | Estimated Cost |
|---|---|
| Crankshaft Sensor | $150–$300 |
| Fuel Pump | $300–$700 |
| Ignition Coil Pack | $250–$500 (set) |
| CAS Module Reprogramming | $400–$900 |
| Battery (Registered) | $250–$400 |
Final Thoughts
A BMW that cranks but won’t start is typically due to one of five things: no fuel, no spark, failed crank sensor, key recognition issue, or fuel pressure loss. By following a structured diagnostic approach, you can avoid unnecessary parts swapping and costly repairs.
Still stuck? Start with scanning for codes, check spark and fuel pressure, then work your way toward sensors and the immobilizer system. With a few simple tools and a focused plan, you’ll get your BMW running again in no time.