Electric nightmare Skoda Superb 3U

[BNY-SNK]

Hello everyone 

I'm new around here and I'll use this post to introduce my turdbox!
There's this Skoda Superb 04 plate 1.9 AWX w/ 336k km's on it that I've been daily driving for about a year now and I have to admit it's a great car - only the wiring on it has been massacred by the old owners and the car was a total of 48 errors on VCDS haha

 

In the past year I fixed most of them but there's one that's stepping on my nerves like nothing else in this world.

16955 - Brake Switch (F) P0571 - 35-00 - Implausible Signal 
Symptoms - Check Engine light ON and the coil thing that usually refers to glow plugs blinking - but not on this car.

 

I've swapped about 3 sensors, then I started checking if they are working. I haven't taken the whole dash out to check the wiring yet as I don't really have the nerves to do it, and If I do it I'll probably fudge it and make it squeak more that it already is.

 

Funny side note is - the car has been left to a garage for a week and a half to get some parts changed, a custom exhaust and custom intercooler piping - and when I took it back the glow plug coil light was gone so I was really excited about that but then I thought the bulb died or something hit the fan - as it goes with VAG cars when lights go out - so I plugged VCDS in it and as soon as I pulled the codes out of the engine module, the coil light came back and is still blinking to this day.

 

Anyone else encountered this? Managed to fix it? Know a magician that knows a trick?

 

Thank you,

Benny

[J.R.]

Replace the brake switch, there are 2 sets of contacts, one that speaks to the body control module to operate the brake lights, the other to the ECU to tell it to ignore any throttle input.

 

People sometimes shunt the 2nd contact to allow them to left foot brake, your car sounds like it has been modified & tuned so its a strong possibility.

 

If the ECU records the engine being used for hundreds of hours without the brakes being used it will generate the implausible signal fault code.

 

Not sure why you have been mucking about chnaging other sensors and looking at the wiring unless you thought that the brake switch must be working because the brake lights do.

[Breezy_Pete]

Are the brake lights all working, including the high level one? Any bulb substitutions with LED type?

[BNY-SNK]

Sorry, forgot to mention that all brake lights are working, including the top one. It seems like the issue is w/ the digital side of things, not the analog bit.

[Breezy_Pete]

When you said you changed about 3 sensors, you meant brake pedal switches, yeah?

The wiring to the engine ECU is the inner two wires of the 4-way connector, pins 2 and 3.  Pin 2 (red/grey wire) should have continuity to engine ECU pin 65 after changing colour to a white/red wire at pin 12 of a white 15-way connector in the plenum.

Pin 3, red/white wire should have 12V when engine is running.

[BNY-SNK]

Quote

Replace the brake switch, there are 2 sets of contacts, one that speaks to the body control module to operate the brake lights, the other to the ECU to tell it to ignore any throttle input.

 

People sometimes shunt the 2nd contact to allow them to left foot brake, your car sounds like it has been modified & tuned so its a strong possibility.

 

If the ECU records the engine being used for hundreds of hours without the brakes being used it will generate the implausible signal fault code.

 

Not sure why you have been mucking about chnaging other sensors and looking at the wiring unless you thought that the brake switch must be working because the brake lights do.

 

By "I swapped about 3 sensors" I meant that I replaced the brake switch with 3 different ones from different manufacturers including an OEM one, that's why I assume it's a wiring issue @J.R.

[BNY-SNK]

1 minute ago, Wino said:

When you said you changed about 3 sensors, you meant brake pedal switches, yeah?

The wiring to the engine ECU is the inner two wires of the 4-way connector, pins 2 and 3.  Pin 2 (red/grey wire) should have continuity to engine ECU pin 65 after changing colour to a white/red wire at pin 12 of a white 15-way connector in the plenum.

Pin 3, red/white wire should have 12V when engine is running.

That's great info! Thanks for that - I'll update here when I have an update
Thank you loads!!!

[J.R.]

1 hour ago, BNY-SNK said:

 

By "I swapped about 3 sensors" I meant that I replaced the brake switch with 3 different ones from different manufacturers including an OEM one, that's why I assume it's a wiring issue @J.R.

 

In which case whoever may have been playing with it may have shunted the contact elsewhere or broken the circuit dependant on whether the contact monitored by the ECU is N/O or N/C.

 

The next thing to do is get a wiring diagram, find the colours of the 2 pairs (I assume) of wires & specifically the one for the contact monitored by the ECU, with the plug disconnected you should see I believe 5v across them, if not then check the voltage of each conductor to battery negative and also the resistance across them.

 

If zero resistance then it has been shunted somewhere, try driving the car and braking very gently while keeping your foot on the throttle, after a very brief delay the engine power should cut, if it doesn't then the ECU sensing wires have been tampered with, either shunted or cut dependant on whether the contact on the switch is N/O or N/C.

[Breezy_Pete]

It's normally closed, circuit broken by pressing pedal.

Wiring colours etc already posted. 

[J.R.]

Thanks, the notification took me straight to the post by BNY-SNK without me realising that you had posted before.

 

12v & not 5v from the ECU duly noted.