This has been doing my head in for a while... Once the car is warm its fine, but you know those first couple of junctions after a cold start and you have to blip it so as not to stall.
I think I have the solution - at least on my car and a good bet on others.
Every once in a while I was getting a fault code for no vehicle speed input at the ECU. It would pop up some days then disappear for weeks. The speedo also worked perfect so I figured it was a glitch. I knew the ECU has the vehicle speed signal (VSS) input but remembered it as something related to HVAC integration. Turns out my memory was only half right.
Long story here - pull up a frickin seat
I was researching an ABY conversion for a local UR owner and was pulling my hair out going thru all the wiring diagrams and data I could find on the old green digidash to see where I could find the VSS signal - it is generated by the speedo in the S2 but not on the UR.
As I was reading up, I realised that VSS is also used as part of idle air control on the ABY engine.
What I couldn't understand was how URs had cruise control but no VSS from the dashboard... Then I discover that the speedo sensor input goes straight into the cruise module of a UR so it works off the raw signal.
Without any time to hook up the sillyscope and try to watch that and drive at the same time - to try and see if the VSS output from speedo was electrically different in some way... I figured 'fuggit' and came up with a plan so cunning you could pin a tail on it and call it a weasel.
Out with the VAG1551 / VAGCOM and into ECU measuring block 004 - sure enough at no matter what road speed, the ECU is 'seeing' 4kph (the lowest it can display). Speedo is fine and no fault codes...
So then I pop off connector T10 above the drivers pedals (this stops speedo & tacho working and triggers an oil light but bear with me). I modify a little spade connector and bridge pins 9 (the raw signal from gearbox) and 8 (VSS from speedo to ECU)... No fault codes.
Off I drive and now I am seeing vehicle speed in Block 004 - then I noticed I wasn't getting the suicidal idle that happens so often.
This means a few things -
1 - The ABY is really fussy about when and why it declares foul on that VSS signal.
2 - I need to get a scope on to see if the root source is that my speedo isn't generating the signal (I assume it is just a buffered output) or if the 332 ECU connector extractions on my car have frigged a wire somewhere.
3 - I can get the ABY running in the UR with VSS coming direct from G22
4 - I should be doing this **** for a living
I think I have the solution - at least on my car and a good bet on others.
Every once in a while I was getting a fault code for no vehicle speed input at the ECU. It would pop up some days then disappear for weeks. The speedo also worked perfect so I figured it was a glitch. I knew the ECU has the vehicle speed signal (VSS) input but remembered it as something related to HVAC integration. Turns out my memory was only half right.
Long story here - pull up a frickin seat
I was researching an ABY conversion for a local UR owner and was pulling my hair out going thru all the wiring diagrams and data I could find on the old green digidash to see where I could find the VSS signal - it is generated by the speedo in the S2 but not on the UR.
As I was reading up, I realised that VSS is also used as part of idle air control on the ABY engine.
What I couldn't understand was how URs had cruise control but no VSS from the dashboard... Then I discover that the speedo sensor input goes straight into the cruise module of a UR so it works off the raw signal.
Without any time to hook up the sillyscope and try to watch that and drive at the same time - to try and see if the VSS output from speedo was electrically different in some way... I figured 'fuggit' and came up with a plan so cunning you could pin a tail on it and call it a weasel.
Out with the VAG1551 / VAGCOM and into ECU measuring block 004 - sure enough at no matter what road speed, the ECU is 'seeing' 4kph (the lowest it can display). Speedo is fine and no fault codes...
So then I pop off connector T10 above the drivers pedals (this stops speedo & tacho working and triggers an oil light but bear with me). I modify a little spade connector and bridge pins 9 (the raw signal from gearbox) and 8 (VSS from speedo to ECU)... No fault codes.
Off I drive and now I am seeing vehicle speed in Block 004 - then I noticed I wasn't getting the suicidal idle that happens so often.
This means a few things -
1 - The ABY is really fussy about when and why it declares foul on that VSS signal.
2 - I need to get a scope on to see if the root source is that my speedo isn't generating the signal (I assume it is just a buffered output) or if the 332 ECU connector extractions on my car have frigged a wire somewhere.
3 - I can get the ABY running in the UR with VSS coming direct from G22
4 - I should be doing this **** for a living
Comment