A3 c circuit reference.

[white_shepherd86]

You need to suspect and may need to unplug every 5v Sensor connected to that ECU. Regardless of Circuit a, b, c or d. Often they are all connected in the module !!

First cut the wire that feeds the pedal - What you got.

It hasn't faulted again since so I haven't looked near it again

 

[Dr Sheldon]

It hasn't faulted again since so I haven't looked near it again

That 5v missing from Gas Pedal was a VERY common failure on the Vauxhall / Opel's with the stupid Hybrid ECU's bolted directly onto the cylinder head - Great place to mount an ECU - Not !

Never ever seen it on a VAG !

 

[white_shepherd86]

That 5v missing from Gas Pedal was a VERY common failure on the Vauxhall / Opel's with the stupid Hybrid ECU's bolted directly onto the cylinder head - Great place to mount an ECU - Not !

Never ever seen it on a VAG !

The ECU is out under the scuttle panel below the wipers on this A3 and is very corroded looking, my brother in law said the fault first occurred when there was Really heavy rain, so maybe something seeped in. Have spare ECU now anyway so will have to wait and see how long it runs for.

 

[Dr Sheldon]

The ECU is out under the scuttle panel below the wipers on this A3 and is very corroded looking, my brother in law said the fault first occurred when there was Really heavy rain, so maybe something seeped in. Have spare ECU now anyway so will have to wait and see how long it runs for.

Yep ! seen VAG ECU's go pop many a time - Just saying !! Never for a throttle pedal 5v fault.

 

[TTT]

That 5v missing from Gas Pedal was a VERY common failure on the Vauxhall / Opel's with the stupid Hybrid ECU's bolted directly onto the cylinder head - Great place to mount an ECU - Not !

Never ever seen it on a VAG !

Only on the long pieces of ultrasonic welden aluminium internal wiring.

 

[white_shepherd86]

Yep ! seen VAG ECU's go pop many a time - Just saying !! Never for a throttle pedal 5v fault.

I suspect the pedal got saturated with water and shorted, shutting down the ECU. TTT you never got back to me about how a 5v supply could give me full throttle. Keen to know.

 

[TTT]

I tried to make a sketch.

There are some assumptions made, on the design and construction of the engine ecu.

5V are now place in common, due to the connection you made for both potentiometers of the gas pedal.

If (assumption made), there is a common 0V inside ecu, and that connection fails, both signal wires will go to 5V, because there is nothing to pull these signals down towards 0V anymore. ECU will see this as full pedal. Unless software will reject 5V as valid value being above a threshold, but again, an assumption.

These systems are normally designed with multiple failure redundancy in mind, no maker wants trouble and publicity that cars went full speed uncontrolled. What you have made is to remove one protection layer already. You would think, it cannot happen to me. Boeing had the same with the 737 .... look how many deaths. Same problem there also.

Another option is that these signals are mirrored, so if ECU sees 5V both, reject ... that could do as well, but who knows....

Long story short, why for the love of God, risk this?

 

[Dr Sheldon]

TTT you never got back to me about how a 5v supply could give me full throttle. Keen to know.

both signal wires will go to 5V, because there is nothing to pull these signals down towards 0V anymore. ECU will see this as full pedal.

Another option is that these signals are mirrored, so if ECU sees 5V both, reject

There are 2 signals in the throttle - always !

I have seen a few variations

• Signals Mirrored / Opposite.
• One signal twice the Voltage of the other - They will always add up to 5v as a check
• One PWM and One linear Voltage.

• Adding that 5v, from I know will do no harm - The system is well engineered to protect against that !

That said !

I do agree with @TTT

Long story short, why for the love of God, risk this?

 

[white_shepherd86]

I tried to make a sketch.

There are some assumptions made, on the design and construction of the engine ecu.

5V are now place in common, due to the connection you made for both potentiometers of the gas pedal.

If (assumption made), there is a common 0V inside ecu, and that connection fails, both signal wires will go to 5V, because there is nothing to pull these signals down towards 0V anymore. ECU will see this as full pedal. Unless software will reject 5V as valid value being above a threshold, but again, an assumption.

These systems are normally designed with multiple failure redundancy in mind, no maker wants trouble and publicity that cars went full speed uncontrolled. What you have made is to remove one protection layer already. You would think, it cannot happen to me. Boeing had the same with the 737 .... look how many deaths. Same problem there also.

Another option is that these signals are mirrored, so if ECU sees 5V both, reject ... that could do as well, but who knows....

Long story short, why for the love of God, risk this?

Thank you. From my own experience I would have thought there is a max threshold for the signal voltage returning to the ECU so if a value above what max throttle would be i.e 5v returning to the ECU it would shut down as it knows that's not the values it should be. Thanks again for your advice.

 

[Dr Sheldon]

Thank you. From my own experience I would have thought there is a max threshold for the signal voltage returning to the ECU so if a value above what max throttle would be i.e 5v returning to the ECU it would shut down as it knows that's not the values it should be. Thanks again for your advice.

Being a 5v Sensor its working range will be from ~0.5v to ~4.5v. For reasons of error detection below 0.5v will cause a Short to Ground DTC and above 4.5v will trigger Short to Positive.

And the 2 signals will be monitored and crosschecked for plausibility thousands of times per second.