18047 - Accelerator Position Sensor 1/2 (G79/G185) and 01314 - Engine Control Module

[ianlovatt]

...And behind door number 13 on the advent calendar was these two fault codes (see full scan attached).

Today the car went into limp mode with warning triangle light and flashing coil light. Turn it off and restart and the car behaved fine again for a short while and then did it again. I cleared the engine and ABS fault codes in the attached scan and they reappeared so they seem to be linked to the problem.

Searching around this sounds like water in the ECU enclosure... which for the first time in the car's 17 year life I took off earlier this year to see if it was the cause of the car not starting. That turned out to be the starter motor:
Please Help won't start (no cranking) 53 plate 1.9tdi

Given
ESP light
and
Guide: ESP Light On- Glow-Plug/Engine Light Flashing - Cause & Fix Inside! | Audi-Sport.net
(good looking guide to sorting this in the second one)

I think I'll be looking for a dry spell (accompanied by flying pigs) here in Yorkshire in the near future to have another fettle with the ECU enclosure.


Couple of questions

1) Does this sound like it could be water ingress into the ECU enclosure to other people?

2) Our drive is sloping - is it best to park the car up the slope or facing down the slope to prevent water pooling around ECU enclosure seals?


Cheers,
Ian


EDIT: Added an image of the measuring blocks for the throttle - this is when the pedal was fully depressed. This wasn't when the issue was happening but thought I'd post it anyway (sat on the drive with the engine off but ignition on)

[ianlovatt]

Had a play with the car this evening. The warning lights come on the moment I touch the accelerator pedal now and the measuring blocks just remain at 0% now (see attached image) vs going up to ~67% last night in my post yesterday. I'm a bit confused why it didn't go to 100% when fully pressed yesterday but maybe that's all part of the water getting progressively worse.

Opened up the ECU enclosure and removed the lower part of the dash to get at the electrical gubbins this evening. Everything seemed dry! Not sure if I'm looking in the wrong place but given some of the horror stories I've read of people finding wet footwells and drowned ECUs but there was no obvious (to me) signs of water...

Shared album - ian lovatt - Google Photos
Shared album - ian lovatt - Google Photos

I wriggled into the footwell and had a good look and feel about where the seal from the plastic ECU enclosure meets the car body and couldn't find any water.

I had the car running with the blowers firing into the footwells plus a hair dryer going for a good hour and half but it didn't seem to make any difference

Can anyone advise where to check in particular for damp?

Is there any chance this isn't water?


Any help on this would really be appreciated!
Ian


Finally this is my creation for getting the back two torx30 bolts in case that's of help to anyone in the future
Shared album - ian lovatt - Google Photos

[ianlovatt]

OK it must be water in the connectors underneath/behind the ECU enclosure - I hadn't realised they are the key thing to check as per
audi A4 avant accelerator pedal problem

some other threads recommending this
Flashing glow plug light and no accellerator!! | Audi-Sport.net
Accelerator Position Sensor: Implausible Signal (diagnostics on 1.9 TDI 130) | Audi-Sport.net

So to be clear for anyone reading this it's not the state of the contacts down at the accelerator pedal sensor (I checked these and they were all still clean and dry - which isn't surprising)

I'll be taking that damn ECU cover off again at lunch and if needed removing base as well to get at connectors

Ian

[ianlovatt]

Wrestled the base of the ECU enclosure off to get to the connectors properly (worth slackening wiper mechanism under the scuttle to make this easier).

No sign of any corrosion in the connectors!
Shared album - ian lovatt - Google Photos

I don't think there was any signs of major water ingress in the past around the seal either
Shared album - ian lovatt - Google Photos
Shared album - ian lovatt - Google Photos

Gave things a good spray with contact cleaner and hair dryer but made no difference.

Had a panic when the ESP light started staying on before I'd even touched the accelerator and gained a new fault code
01826 - Sensor for Steering Angle (G85); Supply Voltage Terminal 30

but it turns out this is normal after the connectors have been removed and after I recalibrated the steering sensor it cleared
Audi A4 (8E) Brake Electronics (Bosch 5.7) - Ross-Tech Wiki


So I guess I really do need to look at the accelerator pedal sensor...

[ianlovatt]

<rant>
Ha so having uprooted my wiring loom and ECU (in the process dropping a t30 bit into the plenum chamber which I cannot for the life of me work out where is hiding! ..maybe it dropped through one of the drainage holes) it turns out because solder resist (Solder mask - Wikipedia) is too expensive for the back of the PCB one of the tracks (a positive feed I think) to the divider circuits in the sensor has died. Vorsprung durch technik indeed...

Shared album - ian lovatt - Google Photos
</rant>


So they have a pretty funky setup on these divider circuits
Shared album - ian lovatt - Google Photos

I can't work out what the solder resist on one of the the inner circuit 's resistive strips (they can afford it here where they don't even need it?!) is supposed to do other than baffle someone probing at the pins expecting both divider circuits to give continuous readings?

Across pins 5&6 and 3&4 I had a bout 1kOhm with pedal at rest. If I push the pedal 3&4 gradually increased to 1.7kOhm while 5&6 immediately go open circuit - as I think they should because the solder resist cuts the resistive carbon(?) strip in two thus breaking the circuit. The other "unnecessary" bit of solder resist chops the resistive strip off from pin 1 which I think is just to confuse people?!

Anyways my problem seems to be that the only actual resistive strip in use for the full range of the pedal is has a break in the track between one end and pin 2 (the positive feed I think).

I might try and tack on some wires but there's a few physical constraints to replace these tracks that are suffering on the back of the PCB

Failing that it's time to get a whole new pedal.

So my question to the audience would be do I get a second hand one off ebay for ~£20 or do I get a new one?

My worries for second hand are that this seems to have failed because of the design (no sign of any acute water damage it's just 17years in the footwell for a bare copper track is a crap plan) so presumeably other second hand ones being a similar age will be prone to doing this?
My worries for new are they're expensive only found one here so far https://www.*******.co.uk/hella/10117984 for £72 and I presume if I call up audi parts it will be double that...

Thanks,
Ian

PS I thought the whole point of two circuits was for redundancy and safety... seems that the only time the ECU gets two reliable readings is when the pedal is at rest? although I guess its unlikely for a situation to occur where someone takes their foot off the pedal and both circuits give the impression it's still pushed.... hopefully :s

[ianlovatt]

So I assume that the site I tried to link of should not be spoken of here hence all the *** replacing it?? I've never used them so no idea if they're good or bad.

Thought I'd post the part number on my pedal 8E2721523C

[philipharmes]

Thanks for sharing all this info Ian.
It's always usefull stuff for when anyone gets a similar problem.

I usually plump for eBay for secondhand parts & havn't been dissapointed with a duff part yet, touch wood.

That pedal sensor has a seal all the way around the periphery, so I guess the water got in via the spindle.

Hope you get a replacement ok & get back on the road fault free.

[ianlovatt]

Cheers for the reply - Saved this thread from being a complete monologue from me!

Following my "decision avoidance" lifestyle values I've tacked some wires on to replace broken tracks on the PCB and it's sprung back to life so haven't needed to confront the second hand Vs new dilemma but I think I will go with second hand if I do need to get one. I could buy a lot of second hand ones for the price of a new one and they're dead easy to replace.

Is there any calibration needed after fitting a new accelerator pedal? I'm assuming not as vcds showed throttle position now going from 0-100% but I came across "throttle body alignment" and although I haven't looked it up yet it seemed like it might be relevant...

Thanks
Ian

Thanks for sharing all this info Ian.
It's always usefull stuff for when anyone gets a similar problem.

I usually plump for eBay for secondhand parts & havn't been dissapointed with a duff part yet, touch wood.

That pedal sensor has a seal all the way around the periphery, so I guess the water got in via the spindle.

Hope you get a replacement ok & get back on the road fault free.

[ianlovatt]

Right I think that's the end of this for me (famous last words) the accelerator is back on and working ok after a 20min drive about this evening.

I don't think throttle body alignment is necessary on diesels according to this so no need to do that for me:
Please Help Help running Throttle Body/Valve Alignment
Throttle Body Alignment (TBA) - Ross-Tech Wiki

Here's the back of the board where the tracks failed
Shared album - ian lovatt - Google Photos

And here is the board repaired
Shared album - ian lovatt - Google Photos

I've lacquered the back of the board in the hope that'll help save the one remaining track should any moisture get in