Please help - EPC Light/ Brake light issue

[dfc101]

Hi all,

I'm having what seems to be a fairly common problem among some VAG lines with a 2003 1.2 Mk4 Petrol Ibiza Sx:

During acceleration (across all gears) there is a sudden power loss which is resolved by taking foot off the accelerator and then reapplying (it can also be resolved by left foot braking with right foot still on accelerator). This can be intermittent and sporadic which suggests an electrical fault. It fired up an EPC code on to the dash. From searching around I found the most likely reason for this was a fault brake light switch. I plugged in and read the codes and it backed this up – saying that the brake light switch was failing.

I acquired a genuine part from a Seat dealer and replaced the brake light switch. The car ran fine for a few miles before suffering the same problem again. I did however notice that the lower brake lights (ie not the boot lid centre light – this operated correctly) were always on when the lights were turned on.

I haven't got the opportunity to read codes again for about a week as I borrowed the kit from a friend. So until then, does anyone have any ideas what could be causing the fault? Would replacing the brake light bulbs be a good idea given its cheap to do? Am I focusing too strongly on the brakes, could it be something else?

Notes:

The cars recently been serviced (minus bulb replacement), had a clutch replacement, and has had a new MAP sensor fitted a couple of weeks before this fault occurred. Other than that it's been a smooth runner from purchase. It's only got 50k on the clock!

I've noticed moisture buildup in the rear lights recently and am wondering if this could have caused a problem at the bulb socket?


Cant think of any other info I'm missing!




Thanks for any input,

Dave

 

[Nath.]

Hi all,

. I did however notice that the lower brake lights (ie not the boot lid centre light – this operated correctly) were always on when the lights were turned on.

You sure that the brake light bulbs are fitted the right way round? If they are the twin filament ones you can get them in 180 degrees out and then the brake light becomes the tail light and vice versa. This means that the brake lights are then very dim and are flooded by the over bright tail lights. Other than that I can remember reading that the brake light switch must be the exact part number as there are a few variations of the part.

 

[dfc101]

I'll check this when I finish work but it's been so long that the bulbs were replaced that it's quite odd that they would suddenly start to throw up an error, or is it? I was considering just fitting new ones for the process of elimination anyway.

I'll also double check the part number again but I'm almost certain it was the exact same part.

Either way it seems like its going to be something annoying simple to fix, it's just isolating the issue thats hard. I've been looking at similar threads and reading this sort of thing:

" it turns out that when a new brake bulb was installed a while back it was installed incorrectly. it worked fine but the problem was that since it was a dual filament, when it was installed at 90 degrees to normal it was completing the left side of the brake light circuit when the side lights were turned on which made the car go into limp mode, obviously thinking the brakes had been pressed at the same time as the accelerator, the EPC light then came on because of this"

And from another forum: "as I said the brake light switch is a dual switch, one circuit powers thee brake lights and sends a signal to the ECU and the other only sends a signal to the ECU, they must match. If the ECU signal is not there but the brake light one is, the lights will work and the ECU will recognise a problem and put on the EPC light, it is extremely unlikely to be anything wrong with the computer"

 

[dfc101]

An update on this........

Picked up some new bulbs from Halfrauds (8 quid down to 1.50 with a trade card!). Replaced the body mounted brake lights and left the central brake light. All the lights seem to be fully operational now and the problem went away. Until....

After about 25 miles or so of smooth riding the car started "kangarooing". Fiercely revving itself when idle and even with the clutch fully engaged and foot off the accelerator. Revs were ranging between 500 and 2000. A mechanic mate has suggested its the throttle body that's faulty so it has no idea how much air to regulate.

Everything up until now has been relatively cheap to fix but looking around a second hand working throttle body is around 70 quid. A new, genuine, part is around 200 and I've also read the ECU needs to be recalibrated/remapped when a new throttle body has been fitted.

Does anyone think it could be anything other than the throttle body, or have any suggestions as to fixing the problem without forking out around 250 quid!?

Cheers,