02 E46 325i auto - trans light on intermittently

[TonyRPH]

The car had 136k miles on the odo.

About a month ago the car got a bit of an Italian tune up, and upon arriving home the trans light came on.

The car has seen little use (about 20 miles each weekend) since then, but yesterday when I started it, upon selecting gears I got an almighty thump as it passed through reverse and into drive. I immediately put it back into park at which point I noticed the trans light was on (it may have been on when I started the car but I didn't notice).

I stopped the engine, waited a few seconds and restarted at which point the gearbox was fine, and went out for a drive with no further issues.

Unfortunately I don't have a code reader for that car, but a bit of internet research suggests an oil change is required?

I think it's a ZF gearbox (model unknown).

From memory there's a place in Lancashire (might be Preston?) that does oil changes. Any recommendations?

I'm based on the North West.

Thanks in advance.

[danb79]

Hi Tony

Poor voltages can cause this too; start with the battery and see what the voltages are first

Secondly; the switch on the side of the box can cause similar issues too; I replaced the one on my previous Jap import E39 540i as it was doing similar

Speak to Grant at Automatic Transmissions, Preston - he'll soon have you sorted: https://automaticgearboxrepairs.com/

[TonyRPH]

danb79 said:

Useful stuff.

Thanks Dan, I'll get it checked.

[davettf2]

10 to 1 its the gear selector switch. I've now replaced this twice. They seem to suffer if the car is not used regularly. Plus its a reasonably cheap fix compared to a gearbox oil change, which should be done at 80000 plus miles Don't believe the sealed for life!

Cheers
Dave

[TonyRPH]

davettf2 said:

10 to 1 its the gear selector switch. I've now replaced this twice. They seem to suffer if the car is not used regularly. Plus its a reasonably cheap fix compared to a gearbox oil change, which should be done at 80000 plus miles Don't believe the sealed for life!

Cheers
Dave

The low battery explanation provided by Dan is a more likely problem in my case I think - as the car is only used once or twice or week (although for 30 mile journeys).

Is the gear selector switch moved by the gear lever?

[danb79]

TonyRPH said:

davettf2 said:

10 to 1 its the gear selector switch. I've now replaced this twice. They seem to suffer if the car is not used regularly. Plus its a reasonably cheap fix compared to a gearbox oil change, which should be done at 80000 plus miles Don't believe the sealed for life!

Cheers
Dave

The low battery explanation provided by Dan is a more likely problem in my case I think - as the car is only used once or twice or week (although for 30 mile journeys).

Is the gear selector switch moved by the gear lever?

Yes. It has a carbon track that wears and causes issues. It'll generally throw an error code of 3C

Low battery is why there's a clunk. It's dropping into limp mode by the sounds of it

[TonyRPH]

danb79 said:

Yes. It has a carbon track that wears and causes issues. It'll generally throw an error code of 3C

Low battery is why there's a clunk. It's dropping into limp mode by the sounds of it

I finally got a copy of BMWScan and after much pain getting it to work, I do indeed have a 3C error.

EGS -> 3C/21 - Gearbox Switch

I've yet to clear the error and test again, as following a recent CCV replacement, the car has now developed an overheating issue, and it's also leaking oil from somewhere at the front... (either gearbox or pas).

Old BMWs eh? Who would have them!!!

[2 GKC]

Can the gearbox switch issue also throw up an engine management light? Having a nightmare trying to get the EML and gearbox lights sorted by my local garage.

How much roughly is it to have the switch changed?

[TonyRPH]

2 GKC said:

Can the gearbox switch issue also throw up an engine management light? Having a nightmare trying to get the EML and gearbox lights sorted by my local garage.

How much roughly is it to have the switch changed?

I don't believe the gearbox switch can bring up an EML light - only the TRANS light (and the gearbox makes some really bad thumps when selecting gears) - restarting the engine usually clears it until the next time.

Has your garage run a diagnostic on it? The switch issue gives a specific code.

On mine, the EML light came on when the exhaust camshaft sensor failed (I seem to recall it does the same with the crank sensor and inlet camshaft sensor as well).

[2 GKC]

Thanks, Yes they got the gearbox switch code when they looked at it this morning. They have spent ages trying to clear the engine management light but nothing seems to be working. Runs fine so it’s a bit frustrating. That said they haven’t done what you mentioned.

Any idea on cost of doing the gearbox switch?

[TonyRPH]

2 GKC said:

Thanks, Yes they got the gearbox switch code when they looked at it this morning. They have spent ages trying to clear the engine management light but nothing seems to be working. Runs fine so it’s a bit frustrating. That said they haven’t done what you mentioned.

Any idea on cost of doing the gearbox switch?

The switch is roughly £100 (used on Ebay) and will likely need overhauling (cleaning) before fitting.

It's probably just as easy to clean your existing switch - the contacts get dirty and tend not to make proper contact intermittently - there are Youtube video showing how to do this.

I've no idea how much labour will cost to remove and refit - from what I've seen on Youtube, it's mounted on the side of the gearbox fairly high up, so access might be a bit tight.

By the way, when the sensors (exhaust sensor in particular) fail, you'll usually notice a reduction in low end performance in particular, and the car may even idle a bit rough.

Your garage must surely have a suitable diagnostic tool to read the codes? Which model is your car?

[2 GKC]

It’s a 2002 330ci auto convertible on 70k miles. Doesn’t get a lot of use. It does seem a bit sluggish at low revs and does idle a little roughly so maybe it is that. Garage said they couldn’t see any codes related to the EML though. Think I’ll take it to a specialist.

[TonyRPH]

Sluggish at low revs definitely points to one of the camshaft sensors.

When the crank sensor fails, often the car won't start at all (or can take a lot of cranking to get it started).