E46 325i - will not start on key, O2 sensor error, misfires.

First post .

My 2001 325i refuses to start - cranks very slow and click, and the headlights come on despite not being turned on and it sounds like the climate control vents are going crazy under the dash. Battery shows 11.8 V when not running. It starts when jumped from another vehicle.

Also, the CEL is on and error code P1155 is showing, along with misfire codes on four cylinders. P1155 is "intermittent O2 sensor, bank 2, sensor 2."

Leading up to this has been a smell of fuel from the exhaust and a loss of power, along with increased fuel usage.

Any ideas what I should check first? I've got the sensor in question but I'm not going to fit it in case that's not the problem!

Many thanks,

M.

 

slow crank, clicking and headlights flashing are all flat battery symptoms and 11.8 is pretty low. The fact that it starts when jumped proves it. Get the battery sorted first.

 

Worth checking the alternator voltage first? Expecting 14.3 V with revs?

 

Yes around 14.3V when the engine is running and relatively stable whatever the revs.

 

Just jumped it and got it going, error codes are gone but the idle is a bit lumpy and it still smells of fuel.
Alternator voltage was 13.9 V under load - is that too low?

 

I'd say 13.9V is fine and isn't your problem.

It seems like you have two problems: a worn out battery and a misfire, and if you have a fault code pointing at the O2 sensor that would be a good place to start.

 

Jumped it and took it round the block for five minutes. Turned it off, and tried to start it again, and it started on the key. No misfire (but still ran a bit lumpy).
Battery confirmed?

 

Battery might just need properly charged. The O2 sensor fault could be intermittent, I had a similar problem years back on my E39 528. One day it would be fine, the next running like a bag of spanners. Replace it with a genuine BMW as some aftermarket are rubbish.

Hope this helps.

 

Battery problem sorted... now the running.

Got a new code and new symptom: P0102 (along with P1155) and it dies shortly after being started; needs a few tries and some revving before it'll keep going.
I gather that P0102 is a MAF-related code, but could there be a vacuum leak/CCV blockage causing both codes?

 

Carefully check the large-bore 'bendy' hose which goes post-MAF to the inlet side of things, they perish with time and are especially given to splitting on the underside [hence checking all round....ask me how I know ]. I chose a random year but it looks like you have the same M54 engine I have in the e60.

Part #3 here https://www.realoem.com/bmw/enUS/showparts?id=AN36-EUR-11-2000-E46-BMW-325i&diagId=13_0905

BMW item Nr 13541705209

Hope this helps.

 

The idle is lumpy, but doesn't surge - my previous car was a Mondeo with a torn hose (failed-open CCV caused constant idle vacuum and sucked a breather to shreds) and that had a hunting/surging idle.
Does that fat hose tend to fail on the "knee"?

I'm confused at this - IME a low MAF voltage would cause a LEAN condition, not a rich one... wtf is going on here?!

 

Might be because the pipe is post-MAF? I'm only reporting what I had on my e39. The hose was perished/split both underneath and at where that small pipe/elbow is bonded in.

 

In taking the MAF off to clean it I noticed the downstream boot was split on the inside of the "knee" and the whole thing was covered in cracks.
Ordered a new one - they're <$10 equivalent ;).

 

Hope this is the fix for the problem.

 

I ordered Part #6 as well - only an extra fiver.
Somebody else pointed me to the breather that feeds into the idle control valve as a common failure... I'm going to spending my xmas bonus on hoses at this rate!

 

Good thinking , you may find that one or both aren't in the best of health [they're likely to be the same age after all , and for all the extra cost you're probably just as well while you're in there.

However, part #6 is pre-MAF so I'd have expected the mixture to be 'sorted' if that were the source of the problem, it not being metered air. Anyway, for a £5 you're no worse off and at least you'll have eliminated a possible cause for the problem. Peace of mind is priceless.....

 

I think #6 is post MAF - looks like it's the last stage before the throttle body.
And I think the concertina elbow coming out of it links to the ICV.

 

Oooops! I thought that part #5 went to the underside of the air cleaner housing, but in my defence it's many years since I did it on the e39

 

Replaced pipes, but still starting and running badly.
Tried unplugging the MAF and it starts and runs fine!

 

So it's running on 'factory defaults'. You could try cleaning the MAF sensor very carefully , following the instructions on the product carefully. For all the cost, it's worth trying - do you have any codes stored after unplugging it? I'm assuming the EML light is on while running, or did it go out on startup?

https://www.ebay.co.uk/i/3128823900...78288&itm=312882390073&pmt=0&noa=1&pg=2386202