Throttle Potentiometer Issue

[Nistorph]

Hi,

I’m looking for some guidance please.

I have a T25 fitted with a 1.9 AHU TDI lump. It now, with increased frequency, reverts to some sort of 1000rpm limp home mode whereby it will hold the revs steady and ignores any throttle inputs. A good friend owned the van for 10 years before me, and I’ve owned it for 3 years. He experienced this 3 times in total during this period. This has become a frequent experience for me, typically when starting after a nights camping. Disconnecting the battery for a period of time cancels any codes and helps. Sometimes restarting (ignition off and on again) helps too. When driving it is possible to predict the limp home before it happens as the throttle doesn’t respond quite how you’d expect I.e. full throttle provides acceleration, but not at the rate it would normally.

I don’t have VAGCOM however it’s previously been scanned and revealed 18039/P1631 - Accelerator Position Sensor (G79): Signal too high.

Throttle Potentiometer = Bosch 0 205 001 082
ECU = Bosch 0281001555/556
Family Reference - EDC MSA 15.5-5.2

The throttle potentiometer is tucked away beneath the vehicle, which I understand might not be sensible as these units aren’t fully waterproof.

It’s also been suggested that I might need clutch / brake sensors in the system, which I haven’t got. As a start though, given that the van used to work fine for many years I have initially ruled out introducing brake / clutch sensors.

I intend to swap out the throttle potentiometer for either another under van unit or an internal one incorporating an accelerator pedal from a donor vehicle.

My question is:

How can I identify which throttle potentiometer part numbers will work under the vehicle - as I can’t locate any with all the correct Bosch numbers - typically the final 3 are different. Does this matter?

How can I identify a donor pedal and sensor arrangement for internal used / mounting? Will any similar era 1.9tdi VAG donor suffice? I’ve seen some accelerators with Bosch sensors and others with Hella. Does this matter - are they all standard.

Pedal photo arrangement is from someone else’s van - similar to what I’d like to acheive.

Thanks in advance

Chris

[Nistorph]

… I guess the short version is:

Is there a list of Bosch or Hella throttle position sensor part numbers which are compatible with ECU / ECU Family?

Thanks

Chris

[Aidan]

working the other way around, do you know the exact engine donor's details - ideally a chassis number for the vehicle that the engine ecu and associated parts came from, which is the sort of information that should be kept with the converted vehicle so future owners can get the correct parts and service it - should be normal with any engine swap to keep this information but it rarely seems to be passed on

if the engine installation is a hybrid of some sort then obviously there's more information required - plenty of peeps fitted mixed parts and made them work but future maintenance becomes even harder unless you know what one really is dealing with

[syncroandy]

Hi, as I've been messing with these sorts of things for a while, I may be able to advise.

Firstly, consider the problem may be a wiring/connector fault, not the sender. The pedal circuit is very sensitive and originally had gold pins, with waterproof connectors to eliminate any corrosion risk. In engine-swaps, this can get overlooked, leading to problems later. It may therefore be worth checking the wiring and all connection points are sound.

The cylindrical bosch TDi senders are basically all interchangable, so long as its off some sort of VAG diesel 92>00-ish it should work. There are minor variations of things like the wiring pigtail length and connector type which give rise to different VW part numbers. I'd suggest forgetting about VW and Bosch part numbers, and just buy it based on appearance. Having said that, a quick look on Ebay shows 028907475AJ as being a common pn.  When swapping these parts, getting the pinout correct is critical, and is done off the plug pin numbers not the pigtail wire colours.

The cylindrical senders are considered 'waterproof', engine-bay placement is common, including by VW. So long as the conector is waterproof it should be OK.

The 'pedal' style senders, used from ~98> have a different six-pin pinout, and are not waterproof. They are electrically compatible though.  Pinouts are below.

The two brake-lamp signals are important for safety, and for engine-braking to work. The clutch switch signal is used during gear-changes to make them smoother. The brake and clutch signals are also used for the cruise-control system, if enabled. The brake signal inputs to the ECU can be retrofitted using a relay to provide the 'inverted' signal. The clutch signal needs a switch fitted.

Personally I think anyone whose gone to all the trouble of installing a TDI without these properly wired up is daft, as it will drive like cr*p without, and be at constant risk of limp-home-mode.

The relay is wired as below. The ECU pins are:
'F' brake signal > T68/44
'F47' CCS brake signal > T68/20
'F36' clutch switch signal > T68/17

(NB. The 028906021DT ECU is from an early 'B5' Passat. VW used the previous generation 68-pin ECU for the initial Passat B5's, before switching to 80-pin. There are a few differences in the wiring specific to these early B5 Passats, chiefly for the brake and clutch signals, these are referenced to the 'switched 12v' ECU power supply, NOT to 'sender earth' as on earlier 68-pin ECU's.)

[Nistorph]

Thanks both for your responses - very much appreciated.

I have a fair amount of info from the conversion however no details on the exact donor vehicle, other the type and age.

Dodgy connectors sound a good first shout. Interestingly the van was playing up before I unbolted the sensor to photograph the part number. Once I’d reinstalled it, and disturbed the connector / wires, the van fired up fine.

Will get under the van this weekend to take a look at the connectors.

Chris

[Nistorph]

For anyone who might be interested the issue is now resolved. 2 of the TPS wires near the connection to the loom had become chafed with small areas of bare wire exposed. Rectification of this has sorted the issue. 

Thanks for the assistance.

Chris

[TwinTurbo]

thanks for comming back to provide your solution,