Throttle Potentiometer vs. Engine Wiring Loom

[TimCrighton]

I'm having a fault with my car which is as follows: I wonder if anyone can shed some light on it for me:


The car is a very early '02 (registered 01 Jan 2002). Mini Cooper.

Engine warning light comes on, car falls into 'limp'.

Taken car to BMW (for the moment nameless). They have said its a Throttle Potentiometer fault code, but I need to change the Engine wiring loom at £495.

Now, call me synical but I called MINI Motorsport Centre in the mean time and they've told me that there is a recognised fault in the wiring that manifests itself as a Throttle Potentiometer code, but its actually the wiring. The dealer should have acknowledged this aparently as most of the cars that have been dealt with by the chaps at MMC (formally all at Cooper Works) have been done under goodwill (although no formal recall exists for this part) as its a common fault and is caused by the illogical design of the wiring harness. New harnesses (hence the need for replacement) are stronger in the effected place.

Wondering if anyone has had this fault, and what the result was?

I'm a bit frustrated as the dealer claims to know nothing of the common problem, but yet rather than suggesting replacing the potentiometer as the fault code suggests they instantly recognise the requirement to change the loom... Strange that!!!

[Tara&Paul]

I had exactly the same problem with my 2002 Mini Cooper yesterday afternoon and I fixed it this morning with a zip tie and two inches of black electrical insulation tape, total cost about 15p.

The problem is with the small section of wiring harness that connects from the throttle body back towards the windscreen as it rubs on a corner of the cylinder head.

You will find the problem wire which is about 5mm in diameter and unshielded, between the right-hand side of the engine and the left-side of the cap where you fill up with water, this has a picture of a book on the top.

Basically the wire has rubbed gently against the cylinder head over time, which has worn through the outer casing of the harness. Now you will have an electrical short which will send incorrect data to the ECU causing it to go into limp home mode and sending you to BMW for a big repair bill !!!

To fix this problem, I simply wound black tape around the slightly damaged area and zip tied the harness away from the cylinder head so it will not rub. You will also need to have your EML light reset, if you near St.Albans in Herts I have an OBD 2 tester and I can do this for you?

Let me know how you get on?

Paul.

[TimCrighton]

Have just been out and fiddled with the wire in question. It had got caught on the top exh. manifold heat sheild, so free'd that up, and also pulled it away from the cylinder head (although no tape to hand at the moment). Fired it up, and bingo, both lights went out and it ran fine! I'll tape it up properly later, stupid design though that looking at it carefully, it needs an angled plug to move it away from the throttle body. The quality of the connectors is pretty duff too to be honest. It actually clips to the heat shield - thats a fine idea BMW, lets clip a plastic coated wire to the exh. heat sheild with a metal clip....

Thank you very much Paul.

I'll try this, and keep an eye on it, and if it proves a conclusive fix then I'm going to write a lovely letter to my local stealership!

[TimCrighton]

Taped it all up and took it out for a quick drive, but its dropped back in to "limp" and the lights have come on. Not sure on this now. Will have another look through the wiring again.

EDIT: Did you mean the wire which has about 5 or 6 individual wires as a bundle of wires? I have looked at that, and whilst I can't see any damage to the wires there are slight rub marks on the head, so I've taped each wire just in case....?

[Tara&Paul]

Glad to hear that your MC is running fine again!

Providing that you tape over with electrical insulation tape where the wiring harness has been rubbing, you should have a permenant fix?

The problem that we've had with our Mini's is a very common one which BMW know about. But BMW have been replacing entire engine bay wiring harnesses and charging owners about £500 to fix the problem. Should call them the Stealership?

When I eventually limped my mini home yesterday after going to Mini in the Park, I plugged in my OBD 2 code reader and it gave me three codes: P1125 P1226 and P0171 which are related to the Throttle Body. I've only just replaced the throttle body with a LOHEN 58mm one, so the problem wasn't the throttle body. So I suspected a electrical short, but wasn't 100% sure? So this morning I traced the wiring harness back from the throttle body to check for evidence of rubbing and eureka I found the break within five minutes. Then five minutes later the mini's running 100% again!

I had a similar problem with a rubbing wire on a Nissan 4x4 a few years ago. Although the problem was a bit more serious, the electrical short kept blowing the fuse in the alternator/battery charging circut which would kill the truck, not good! It took me a few hours to find the rubbing wire, but only a few inches of insulation tape and a zip tie to fix it.

Once again, glad I could help.

Regards,

Paul.

[Tara&Paul]

Quote: Originally Posted by TimCrighton (original)

Taped it all up and took it out for a quick drive, but its dropped back in to "limp" and the lights have come on. Not sure on this now. Will have another look through the wiring again.

EDIT: Did you mean the wire which has about 5 or 6 individual wires as a bundle of wires? I have looked at that, and whilst I can't see any damage to the wires there are slight rub marks on the head, so I've taped each wire just in case....?

Tim,

Give me a call on my mobile: 07816 750729 or 01727 832020
And I'm only about an hour away, I could pop down this evening and bring my OBD code reader with me?

Paul.

[TimCrighton]

Paul -

Thank you so much for your help on this. The problem now seems to be resolved.

Was good to meet you and Tara

Tim

[rothbury]

Quote: Originally Posted by Tara&Paul (original)

Tim,

Give me a call on my mobile: 07816 750729 or 01727 832020
And I'm only about an hour away, I could pop down this evening and bring my OBD code reader with me?

Paul.

I have just joined this site after an embarrassing mistake by joining the original Mini site.
I am very interested in your posts with Tim Crichton . I had a fault with my 2001 Mini One
which led to the dealer changing the potentiometer in Nov 2006 . The symptoms were EBSL light on and minimal power which I see now was probably "limp home mode". Could only do about 2000rpm
tops. We thought all was cured then in traffic over the May Bank holiday it did it again both going down to Cornwall and coming back. SO embarrassing! It would eventually revert to normal but cd take quite a long time and switching off then on again would not necessarily do the trick.
It occurred to me after reading your posts that this wiring thing might be the cause as otherwise why should a virtually new potentiometer fail so quickly.
Also why did the dealer not find it out on the diagnostic when we first reported it if it was a failed
p.....ometer. He didn't know what it was until another dealer said that's what it might be.
I am going to try to find the wire you refer to and see what happens .

[richg40]

This fault is not caused by wires chaffing. The cause is the poor quality plug terminals on the throttle plug, loom side. The wiring loom requires replacing, anyother fixes are purely temp.

[rothbury]

Quote: Originally Posted by richg40 (original)

This fault is not caused by wires chaffing. The cause is the poor quality plug terminals on the throttle plug, loom side. The wiring loom requires replacing, anyother fixes are purely temp.

Well we'll have to see but a new wiring loom costs £500 doesn't it - can't they just replace the connectors?

[richg40]

i think you've answered you're own question there.