Glow Plug (mil) Light, A Theory

[GaryM]

I have had a problem with my Galaxy for a while now where the Glow Plug light comes on when driving for now apparent reason or affect on performance and sometimes it will clear shortly after, after an ignition reset Or not.

 

Armed with VAG-COM I checked the ECU and found the brake light switch was logging: 16955 - Brake Switch (F): Implausible Signal.

 

Reading several posts seems to confirm that this is a very common cause. So I took the switch out to take a look (my skills being electrical more than mechanical).

 

My car, a 76,000mile 2000, 1.9TDI 115Bhp Zetec, has only a single Black switch fitted. Upon opening it (not advised :D ) it has two contact blocks. One rated for current, operating the actual lights and the other low current set, I assume, signalling the ECU although I think the ECU monitors both sides.

 

The switch construction is not of a high standards (typical for car electrics) using poor plated contacts as opposed to Gold flashed one used in the electronic industry. I found the contacts to be dirty but the big contacts to have arc'd and become badly pitted. Out with a bit of emery cloth and they are nice and shiny again. Time will tell if it is fixed.

 

Anyway the theory...

 

The extra load of an additional set of brake lights from a trailer board (cycle rack in my case) or towing a trailer causes the contacts to wear quicker and with an older car the switch will just get dirty leading to poor contact and eventual arcing.

 

If I get the fault again I will be replacing the switch with a new one. It will be interesting to see if it is modified (better rated) being a newer part.

[paulmpaciorek]

Had the same prob with my Golf TDI,but it cost me

[GaryM]

At those costs it has already paid for my investment in VAG-COM and a the OBD lead. So if you don't mind getting your hands dirty it seems a worthwhile investment.

[Tigger]

I had this problem twice First time I replced the switch. Second time i just cleaned it both worked