00777 Throttle Position Sensor Issue

eggybread

Member
Joined
Jan 16, 2017
Location
Birmingham, UK
TDI
Mk2 Jetta AHU Swap
Hi guys,

After lerking through this and various other forums about this issue I'm finally posting.

A few months ago I bought an AHU swapped MK2 Jetta. Guy I bought it from informed me of the issue where accelerating past a certain point cuts the revs to 1200rpm and the throttle is non responsive until its given a couple of prods. I was told it would only do this once on start up and drives fine after. Turns out it will do it on first pull away everytime but can catch you off guard whilst driving along as well.

Scanning with vagcom gives the error "00777 Accelerator Position Sensor G79 27-10 Implausible Signal Intermittent". I've heard the glow plug light will flash when this error shows its face but unfortunately one was never wired in, that's next on the list.

I've traced the wiring on the TPS back, tested the continuity across all the wires and the earth. All checks out fine. Tried another TPS. Cleaned all contacts on the T68 plug on the ECU. Unplugged the 4 pin brake sensor (looking at the wiring diagram I think this should be a 2 pin?). Unplugged the MAF. Problem still persists.

I read on the forum that an ECU swap fixed the problem and so I'm looking into sourcing a replacement. Does anyone know the compatibility between ECU's? I'm currently running a 028 906 021 GG and whilst they seem expensive to get a hold of there's a 028 906 021 DK for good money.

If anyone knows the correct wiring on the pins for the brake sensor as well that would be much appreciated.

Cheers in advance.
 
Last edited:

Mike_04GolfTDI

Top Post Dawg
Joined
Nov 19, 2003
Location
Richmond, BC, Canada
TDI
Mine: 2019 Golf R DSG, Wife's: 2015 Golf Comfortline TDI
Was I the one who wrote that an ECU swap fixed the problem?

This happened to me, and yes, an ECU swap fixed the problem.

Years later I took the ECU apart and found that one of the large capacitors inside was bulging, which usually means it has failed. The ECU would kind of randomly work, and then not work. I replaced the capacitor and that seemed to fix it, although I don't trust it enough to use it. I have three ECU's for my Mk4, so no reason to try using the possibly flakey one.

Unless you have a spare ECU, it is risky to take it apart and attempt to fix it. Obviously you'd be left without a running engine if anything goes wrong.
 

eggybread

Member
Joined
Jan 16, 2017
Location
Birmingham, UK
TDI
Mk2 Jetta AHU Swap
Cheers for the advice Mike.

It was dslg60 who posted about changing the ECU but I've seen fair few threads where the issue has been solved after swapping the ECU out so I might have stumbled across yours on my travels.

I've had the ECU apart again today after work and had a look see inside. No bulging capacitors to be found. Gave the thing a once over with some electrical contact cleaner anyway since it was open. Fitted it back to the car and the problem is still there.

Looks like I might have to source another ECU anyway since I can't find a glaring fault elsewhere.

Going off the OE reference number in the table here, http://www.atpelectronics.co.uk/c/vw-vento-diesel-ecu, my only options are 0 281 001 649 and 0 281 001 650 ECU's since mine is a 0 281 001 650. I don't suppose you know if this is the case or if there are other compatible ECU's before I source another?
 

eggybread

Member
Joined
Jan 16, 2017
Location
Birmingham, UK
TDI
Mk2 Jetta AHU Swap
Managed to source an ECU with the exact part number as mine, hopefully that should be here within the next couple of days.

I'll post an update whether it fixes it or not, fingers crossed.
 

eggybread

Member
Joined
Jan 16, 2017
Location
Birmingham, UK
TDI
Mk2 Jetta AHU Swap
Quick update.

Fitted the new ECU and the problem on start up is still there. Unsure of what else there is to try at this point. On the upside I've got a spare demobilised ECU floating about.

Going to take the car out over the next couple of days and see if it decides to throw the 00777 again. Shame it's completely random as to whether it decides to work.

Any suggestions wouldn't go a miss at this point. :)

Cheers
 

Mike_04GolfTDI

Top Post Dawg
Joined
Nov 19, 2003
Location
Richmond, BC, Canada
TDI
Mine: 2019 Golf R DSG, Wife's: 2015 Golf Comfortline TDI
Are you sure the accelerator pedal is meant for a diesel? I saw a thread recently saying the pedal from a petrol car will cause erratic behavior.
 

eggybread

Member
Joined
Jan 16, 2017
Location
Birmingham, UK
TDI
Mk2 Jetta AHU Swap
Part number is 1H2721727A on the TPS which after a quick Google seems to turn up diesel results? I tried the 1H2721727 TPS as well which I think may be the petrol version, didn't seem to change the behaviour although I did only mess with it on the drive and not on the road.

I've driven the a car couple hundred miles over the weekend since the new ECU has been fitted, it hasn't thrown the error code yet and the pedal hasn't decided to stop working.

Turns out it doesn't log that error code when it does it on start up so I'm going to say it's an unrelated issue that I need to chase. No idea what is causing that.
 

DT3

New member
Joined
Nov 7, 2015
Location
long island ny
TDI
06 jetta
Throttle position sensor replacement

Hi , I'm tiring to remove accelerator pedal on a 2006 tdi Jetta replacing tps ,does anyone know how to remove wire harness? Thanks
 
Last edited:

Sport6

New member
Joined
Jun 17, 2018
Location
Birmingham
TDI
T3 1.9 tdi ahu
Ahu no throttle response

Hi guys
I was wondering if this issue ever got resolved?
I have a t3 awith an Ahu conversion that has developed a 00777 fault code, i have changed potentiometer,ecu and battery however still no joy. If I disconnect 3 wire fuel cut off plug when engine is running and restart with foot on throttle it will rev for about 5 seconds!! Has anybody got any ideas? My thoughts are that the pump is faulty
Thanks in advance
 
Top