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BMW 2A9A and 2A9B: camshaft sensor signal invalid for synchronization
The engine computer can't line up the camshaft signal with the crankshaft. On N52 sixes BMW traced many cases to a sticking VANOS solenoid, not the sensor.
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Codes on this page
| Code | Definition | Source |
|---|---|---|
| 2A9A | Cam sensor, inlet signal: signal invalid for synchronization | Vehicle Service Pros |
| 2A9B | Cam sensor, exhaust signal: signal invalid for synchronization | Vehicle Service Pros |
| 2A98 | Crankshaft–inlet camshaft correlation: value outside reference range | Vehicle Service Pros |
| 2A99 | Crankshaft–exhaust camshaft correlation: value outside reference range | Vehicle Service Pros |
P-codes are the generic OBD-II codes any reader shows. Six-character and four-character hex codes are BMW's own, read with a BMW-capable scanner; the wording is BMW's, from the source shown.
What it means
The DME uses the camshaft sensors to time fuel injection and VANOS. When the inlet (2A9A) or exhaust (2A9B) signal doesn't make sense against the crankshaft, it stores these codes, and the engine may be hard to start or run rough. 2A98 and 2A99 say the cam-to-crank relationship is outside its range.
Can I keep driving?
Often yes, but it may not restart. Owners report long cranking or no-start with these codes. Drive gently and get it checked before relying on the car.
Usual causes on BMWs
| Cause | Cars most affected | What you notice | Evidence | Repair prices (national average) |
|---|---|---|---|---|
| VANOS solenoid stuck or contaminated | N52 in E60 and E90 built 3/2005–6/2005 (BMW bulletin), other sixes | Hard starting, rough running, misfire codes. BMW's fix was cleaning the solenoid and a DME update rather than new parts. | Vehicle Service Pros | VANOS solenoids (intake / exhaust) Indie $549–$703 Dealer $973–$1,199 |
| Camshaft sensor or wiring | All | If the code stays on the same side after swapping solenoids, the sensor or its connector is next. | — | — |
| Loose VANOS gear bolts | N51, N52K, N52T, N55 | Rattle plus camshaft sensor and VANOS codes. | SI B12 14 12 (PDF) | — |
A bulletin isn't a recall and doesn't mean your car has the problem; open it for the exact models and build dates. Estimates are national averages built from BMW warranty labor time, regional shop rates and parts prices; open a repair for your ZIP. "Owners paid" is the middle half of sourced prices, shown where we have at least 3.
What to do
- Check the oil level and condition.
- Swap the intake and exhaust VANOS solenoids; if the code follows the solenoid, replace that one.
- If it stays put, test the camshaft sensor and its wiring.
Warnings it can bring up
Sources
- Vehicle Service Pros: "Bimmer bugs" (BMW N52 bulletin summary, cam sensor and VANOS codes), Dec 2013
- NHTSA: BMW technical service bulletins and recalls by VIN
Bulletins are cited in the tables above. Explanations are ours; where a source is an owner report rather than BMW, it is labelled as one.