[lustek]

Hi everyone,

I'm working on a BMW E46 with the M54B30 engine (Double VANOS, single housing). I've been diagnosing this for a few days and I'm stuck – hoping someone with hands-on experience can point me in the right direction.

The problem:
Both VANOS units are completely inactive. Values in INPA are frozen – intake shows approximately +206° and exhaust approximately −105° – and neither changes at any RPM, including when blipping the throttle. The only fault code stored is the exhaust camshaft position sensor (CMP).

What I've already done and checked:

• Exhaust CMP sensor – replaced with a known-good unit, fault returns immediately on startup
  
• Wiring harness to both solenoids and to both CMP sensors – fully checked, no breaks or shorts
  
• Solenoid self-test – when solenoid connectors are unplugged, open-load faults appear instantly, which suggests the solenoids and their drivers are functional
  
• Direct 12V battery test on one solenoid – plunger extends, solenoid is mechanically OK
  
• PWM signal check – connected a 12V test bulb (as a load) to the solenoid connector with the engine running. Bulb lights up immediately and stays at constant brightness regardless of throttle input. No flicker, no dimming. This tells me DME is outputting a steady DC voltage instead of a PWM signal – consistent with it having lost CMP feedback and going into a fallback/limp state
  
• Full VANOS disassembly – all O-rings and seals replaced, piston clearances corrected (there was significant play before the rebuild)
  
• Post-rebuild retest – no change. VANOS still frozen at the same values, same CMP exhaust fault
  

My questions:

1. Could the oil supply to the VANOS unit be the root cause? E.g. blocked oil gallery, faulty oil pressure control valve on the front of the engine, or low oil pressure overall? Could insufficient oil pressure prevent the mechanism from moving enough for the CMP signal to be valid?
   
2. Is there a way to verify VANOS oil supply pressure without specialist equipment?
   
3. Has anyone seen a case where the DME itself caused this – stuck in fallback, refusing to output PWM even with everything else correct?
   
4. Any other checks you would do before condemning the DME or pulling the front of the engine again?
   

Any help or experience with this specific failure pattern would be greatly appreciated.

Thank you.

[Liteace]

check the out put of all 3 sensors, cams + crank, is the cam timing 100% correct, reassembled with cam locking tools?

[lustek]

check the out put of all 3 sensors, cams + crank, is the cam timing 100% correct, reassembled with cam locking tools?

Regarding the sensor outputs – I don't have access to an oscilloscope, so I haven't been able to check the waveforms properly.

As for the cam timing – I have to be honest here. I did not use cam locking tools during the VANOS reassembly, and I have not verified the cam timing since putting it back together. I was not aware this was strictly necessary for this job.

Could this alone explain all the symptoms – the exhaust CMP fault appearing immediately on startup, the DME outputting DC instead of PWM, and both VANOS values being frozen? If so, is there a way to verify cam timing without the locking tools, for example by checking the reference marks at TDC?

[willisodhiambo]

Has anyone seen a case where the DME itself caused this – stuck in fallback, refusing to output PWM even with everything else correct? YES

[inspi1981]

Looks like timing is without specs

[larshutten]

For starters share the exact faultcode you are getting on the exhaust camshaft sensor, also how do you expect vanos to work when it can’t see the position of the exhaust camshaft due to a faultcode? It can’t adjust if it doesn’t know the position of it…

[lustek]

Fault code and signal from exhaust cmp sensor

[lustek]

Added one more oscilloscope capture with all 3 sensors simultaneously at 20ms/div:

CH1 (pink, top) → crankshaft (CKP) – dense regular pattern as expected
CH2 (cyan, bottom) → intake cam (CMP)
CH3 (yellow, bottom) → exhaust cam (CMP)

Both cam sensors show clean rectangular signals with different pulse widths relative to each other. All 3 sensors are alive. Can anyone confirm if the phase relationship between the cam signals looks correct for M54B30, or does it suggest a timing issue?

[Node]

Well, your code clearly says exhaust camshaft sensor SIGNAL IMPLAUSIBLE. I have no idea how anyone can properly assemble BMW engines WITHOUT locking tools...

[lustek]

Well, your code clearly says exhaust camshaft sensor SIGNAL IMPLAUSIBLE. I have no idea how anyone can properly assemble BMW engines WITHOUT locking tools...

I remove only vanos unit, not timing. I dont touch this guys
Also same fault was present before vanos rebuild