VW T4 P0571 Wiring Fault FIXED Brake Light Switch Implausible Signal 16955 Transporter AUDI SKODA

This is for a year 2000 Transporter T4 which has 4 wires to the brake pedal switch. Does not apply to some earlier T4s that have 2 wires to their brake pedal switch.
The brake lights were working fine and all bulbs were good but we still had this fault code. From research on internet this fault is often fixed by replacing the brake pedal switch (several types available so make sure you get the correct one). Ours had already been replaced by the previous owner but the fault remained. There are two sets of contacts within the switch: one provides 12V to the brake lights circuit when the pedal is pressed (continuity through pins 1 and 4), and the other set tells the ECU if the pedal is pressed (breaks continuity between pin 2 and 3). We checked resistance through pins 1 and 4, and pins 2 and 3 with the battery disconnected whilst moving the pedal on and off. That was fine with 0 ohm resistance.
We checked for a good power and ground at pin 1 and 4 (I can't remember which is which) and they were fine.
Then we plugged in VCDS and went to Measuring Block 6 in the Engine module. With no pedals pressed we got 010 but it should have been 000. With brake pedal pressed it read 011 which is correct. We also checked when clutch pedal pressed too and we got 111.
Key:
1** Clutch pedal on
1 Brake Switch on (Pins 2 and 3 open circuit. Tells ECU brake pedal has been pressed)
**1 Brake Pedal Switch on (continuity through Pins 1 and 4 which sends power to lights).
So basically the switch contacts were working correctly but the ECU was always seeing Pins 2 and 3 unmade so we knew that there was open circuit or high resistance somewhere in the wiring from the switch to the ECU (or the ECU was bad)
So we checked inside the conduit that runs across the top of the engine from the bulkhead next to the brake servo, as someone on the VW T4 forum had found damaged wiring inside theirs. We found quite a few damaged wires inside, including a broken purple wire for the brake pedal switch! We repaired the wire and cleared the fault code. We took the van for a test drive and the fault did not return 😁.
This issue can affect multiple systems as many wires to run through that conduit including accelerator/throttle pedal position etc.

[@GrubbyRabbitRepairs]

Hi, see the Description for more detailed fault finding tips. Hope this helps someone! 😁

[@montyludwig]

Thanks mate for the useful video!

[@GrubbyRabbitRepairs]

Glad you found it useful 🙂. Thanks for watching mate!

[@adolg4049]

I have this Needle lift and acelerator position sensor implausible signal ??

[@GrubbyRabbitRepairs]

I know the accelerator pedal position wiring on a TDI runs through that conduit so you definitely could have the same problem of chafed wires. The needle lift sensor is on one of the injectors on a TDI. Not sure where the wiring goes for that

[@adolg4049]

@@GrubbyRabbitRepairs thank u Man but Service shop tell me its Fault of Injection pump Idk What to do Honestly

[@GrubbyRabbitRepairs]

@@adolg4049 I had the needle lift sensor on my T4 go bad and it caused a hesitation while accelerating. Are they mistaking that for a lack of fuel pressure? Have they read the fault codes? They may have used a fuel pressure gauge and found that the high pressure fuel pump is weak but I'm not sure how it would cause those fault codes. I'm not a mechanic though, it's just a hobby for me.

[@GrubbyRabbitRepairs]

When I say the accelerator pedal wiring goes through that conduit I mean for a right hand drive van. I'm not sure of the routing on a left hand drive van.

[@adolg4049]

Codes shows only Needle lift sensor implausible signal acelerator pedal position sensor implausible signal I Have A engine like AlH With no throtle body At all but My gas pedal has Sensor and Cable Idk Really WHEN I PRESS FAST ACELERATOR CAR GOES RPM ITSELF 10+ AND STAYS LIKE THAT and no response acelerator after that i turn of i press slow and sometimes Work nice