Engine Light - Randomly Goes Out?

[GJN]

'02 E46 330i Sport, 152,000 miles

All,

1) I've been having issues with the engine light coming on, usually on a long run of several hundred miles. It's always a lean mixture error. Tried a few things to fix it to no avail. I bought a cheap OBD reader to reset it, since it's never a problem for the vast majority of the year - only long motorway trips for holidays.

Last week it came on, and I left it on so that the local indy could read it (again) and to see if he had any other ideas.

Today, on the motorway, the light went out. It's not the bulb that's gone, because it illuminates with the ignition.

I thought the light would latch "on" until it was reset? Why would it suddenly go out?

 

2) On the aforementioned holiday trip, the cruise control suddenly tripped out. Luckily pressing the accelerator avoided any disasters. Resetting it worked for a while, then it tripped again. Reset again, and it's been fine ever since (about a week). Any ideas? I've also in the past had an issue where the radio volume randomly went up to maximum - which was extremely scary. I'm wondering if this and the cruise control issue might be somehow related to the controls being on the steering wheel - and some kind of rotary contact intermittently failing?

 

Any thoughts on the above much appreciated.

Thanks!

 

[incredirog]

did you read the thread a few below yours bank 1&2 lean errors? it’s very similar to yours, I almost thought it was the same! basically my advise would be if the only thing that bothers you is an intermittent engine management light after a long journey in an almost 20 year old car and the rest of the year it’s completely fine just leave it alone, the fact it goes away means that it is getting itself back within parameters and no longer needs to show the driver a warning. you could spend some serious money fixing something which doesn’t really need fixing. oh and the radio is a common fault and not linked to the cruise control whatsoever.

Edited June 14 by incredirog

[GJN]

On 14/06/2022 at 14:56, incredirog said:

did you read the thread a few below yours bank 1&2 lean errors? it’s very similar to yours, I almost thought it was the same! basically my advise would be if the only thing that bothers you is an intermittent engine management light after a long journey in an almost 20 year old car and the rest of the year it’s completely fine just leave it alone, the fact it goes away means that it is getting itself back within parameters and no longer needs to show the driver a warning. you could spend some serious money fixing something which doesn’t really need fixing. oh and the radio is a common fault and not linked to the cruise control whatsoever.

Yes I read the thread below mine - in fact it’s my thread!

The engine light is annoying rather than critical (I hope!)

If it causes significant engine damage I’ll get another car and be done with it - it doesn’t owe me anything.

It was more the light going out again that I thought was odd.

Cruise control - again it’s scary when doing 70 in a line of traffic on the motorway, but I can live with it.

 

[momo]

Possibly not related but have you checked the alternator is putting out the right voltage when running?

I had an alternator start to fail a few years ago and it would do some really random things like this. The voltage was showing fine when running but every now and then would dip (guessing at this point, I never tested it when it happened because it'd fix itself after a few mins). My glow plug light would come on and randomly some other ones would come on.

Thought F-it - replaced it with a Bosch one. Never had those issues since.

[GJN]

On 19/06/2022 at 08:32, momo said:

Possibly not related but have you checked the alternator is putting out the right voltage when running?

I had an alternator start to fail a few years ago and it would do some really random things like this. The voltage was showing fine when running but every now and then would dip (guessing at this point, I never tested it when it happened because it'd fix itself after a few mins). My glow plug light would come on and randomly some other ones would come on.

Thought F-it - replaced it with a Bosch one. Never had those issues since.

I’ve not considered the alternator.

Strange you should mention it though. My wife’s old Civic SRS light came on. Couldn’t get a code out of it, so took it to several ‘specialists’, who told me the airbag control unit ‘might’ fried, and since no spares are available, it was best to scrap the car since it’s an MOT fail, and obviously a safety issue.

As a last resort, took it to an old school auto electrician. He had it 2 weeks looking at it as and when he had time. He eventually diagnosed an alternator issue (regulator burned out) which caused over-voltage, which in turn tripped the SRS light.

New alternator, and it’s been perfect ever since. 
 

Thanks for the idea - Is there an easy way of checking? Battery voltage when running?

[momo]

12 hours ago, GJN said:

I’ve not considered the alternator.

Strange you should mention it though. My wife’s old Civic SRS light came on. Couldn’t get a code out of it, so took it to several ‘specialists’, who told me the airbag control unit ‘might’ fried, and since no spares are available, it was best to scrap the car since it’s an MOT fail, and obviously a safety issue.

As a last resort, took it to an old school auto electrician. He had it 2 weeks looking at it as and when he had time. He eventually diagnosed an alternator issue (regulator burned out) which caused over-voltage, which in turn tripped the SRS light.

New alternator, and it’s been perfect ever since. 
 

Thanks for the idea - Is there an easy way of checking? Battery voltage when running?

Could use a multimeter but I think there's a hidden menu where you can check

Here you go:

 

[GJN]

9 hours ago, momo said:

Could use a multimeter but I think there's a hidden menu where you can check

Here you go:

 

Thanks very much.