Drive By Wire Fault

[MugelloB7RS4]

Hi everyone, I've got an intermittent problem that I'm wondering if anyone has seen before.

Occasionally when the car is at normal operating temp and I go to WOT, I get a drive by wire fault. Its not everytime either which is weird.

005000 - Control Module Malfunction - DBW Throttle Monitoring
P1388 - 001 - - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10100001
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 248534 km
Time Indication: 0

Freeze Frame:
RPM: 3372 /min
Load: 100.0 %
Speed: 88.0 km/h
Temperature: 92.0°C
Temperature: 27.0°C
Absolute Pres.: 970.0 mbar
Voltage: 13.589 V


This causes EPC light and MIL to come on. Its almost as if the car kills power from the engine because you're only able to coast after that. I've started to get good at turning the car off and then back on again while rolling to reset everything. A key cycle fixes it.

I've read that throttle pedal position sensors sometimes are the culprit. Its as if the throttle pedal position doesn't equal throttle body position sensor and the car goes all wacky.

Has anyone experienced this before on the RS4? My thinking right now is that I'm going to clean the throttle body. There could be something in there that's not allowing it to reach full WOT on the throttle plate. Past that I'm going to replace throttle pedal sensor. Past that I'm likely going to look at the throttle body itself.

Any thoughts?

Thanks

Roy

[MugelloB7RS4]

Update:

I tried a throttle body adaptation, I tried cleaning the throttle body and tried replacing the throttle pedal assembly. Nothing worked.

What I have noticed is that it seems to be more consistent now. If I'm in any gear, and around 3000rpm and I put my foot to the floor, before the tach reached 5000rpms the fault sets.

Anyone had anything like this before?

Thanks

[Hans solo]

Update:

I tried a throttle body adaptation, I tried cleaning the throttle body and tried replacing the throttle pedal assembly. Nothing worked.

What I have noticed is that it seems to be more consistent now. If I'm in any gear, and around 3000rpm and I put my foot to the floor, before the tach reached 5000rpms the fault sets.

Anyone had anything like this before?

Thanks

Need new Tb

[MugelloB7RS4]

Just ordered one......we will see.

[MugelloB7RS4]

I swapped out the throttle body earlier and went for a drive and found it's the same thing. Any thoughts? I've replaced throttle pedal (with a used unit but as far as I know it worked), replaced the throttle body, now not sure what to do.

Any input would be greatly appreciated.


I took a log of the TPS on the throttle body and the pedal. Does anyone know how the pedal sensor work? For example it looks like the two in the throttle body itself sum up to give you roughly 100%. Sensor 1 looks to count from closed while sensor 2 seems to count from open. Is this how the sensors on the pedal should act also?

[Hans solo]

I swapped out the throttle body earlier and went for a drive and found it's the same thing. Any thoughts? I've replaced throttle pedal (with a used unit but as far as I know it worked), replaced the throttle body, now not sure what to do.

Any input would be greatly appreciated.


I took a log of the TPS on the throttle body and the pedal. Does anyone know how the pedal sensor work? For example it looks like the two in the throttle body itself sum up to give you roughly 100%. Sensor 1 looks to count from closed while sensor 2 seems to count from open. Is this how the sensors on the pedal should act also?

did you try the tb adaptation ?

[MugelloB7RS4]

Yea. I did a bunch of them. Both pre and post throttle body change.

Car drives great otherwise. Idles well and runs great except for this.

[MugelloB7RS4]

I figured it out

If anyone is curious it ended up being the MAF. I didn't have any MAF codes, just the P1388 so it was just dumb luck that I figured it out. I was at the dealer and one of the parts guys mentioned a similar issue he's had in the past on another car and it was the MAF. So for shits and giggles I unplugged the MAF and sure enough the car was great. Installed new MAF and all is well again.

Im just glad it didn't end up being the ECU. $200 part vs $2000 is much better.

[jonan]

I figured it out

If anyone is curious it ended up being the MAF. I didn't have any MAF codes, just the P1388 so it was just dumb luck that I figured it out. I was at the dealer and one of the parts guys mentioned a similar issue he's had in the past on another car and it was the MAF. So for shits and giggles I unplugged the MAF and sure enough the car was great. Installed new MAF and all is well again.

Im just glad it didn't end up being the ECU. $200 part vs $2000 is much better.

damn, i was just gonna check to see whether or not you figured this out...

years ago i was trying to track down a CEL in my b6 for the EVAP system, i changed a bunch of shit related to the codes i was pulling and it would always come back...the fix ended up being a check valve that was a few MMs too small in diameter...took me months to figure it out and it didn't dawn on me until i reread the entire engine strengthening thread and noticed in one of the photos that there are a few check valves which are larger than the others that are used throughout the engine bay...

[MugelloB7RS4]

It's funny you should add this because it's not in fact fixed. I think what happened was I disconnected the MAF and it ran great so in my head that pointed to the MAF, but I just didnt think it through. When you disconnect the MAF the ECM uses a different map which looks as less inputs. So the car runs fine when the MAF is unplugged but plug it back in and do a drive cycle or two and it comes back.

My current thinking is its something to do with airflow. I only recall the issue happening since I removed the intake manifold flaps. So looking back, I also have the Gruppe M intake which I believe has a larger MAF housing. So the combination of larger MAF housing and less restriction in the intake might be causing the engine to get more air than it thinks it should be getting. So the increase in air doesn't match the engine speed/throttle position and thus throwing the code. That is just a theory right now, but going to try and dig deeper.

[jonan]

It's funny you should add this because it's not in fact fixed. I think what happened was I disconnected the MAF and it ran great so in my head that pointed to the MAF, but I just didnt think it through. When you disconnect the MAF the ECM uses a different map which looks as less inputs. So the car runs fine when the MAF is unplugged but plug it back in and do a drive cycle or two and it comes back.

My current thinking is its something to do with airflow. I only recall the issue happening since I removed the intake manifold flaps. So looking back, I also have the Gruppe M intake which I believe has a larger MAF housing. So the combination of larger MAF housing and less restriction in the intake might be causing the engine to get more air than it thinks it should be getting. So the increase in air doesn't match the engine speed/throttle position and thus throwing the code. That is just a theory right now, but going to try and dig deeper.

sounds like a valid hypothesis, i'd swap in a stock airbox and see if that resolves the issue...

[MugelloB7RS4]

sounds like a valid hypothesis, i'd swap in a stock airbox and see if that resolves the issue...

Yea, thats one of my plans. I'm on a work trip now, but was thinking of either trying to log the position sensors for the flaps to see if the code is being set in correlation to that flap movement (I have the flaps removed but all linkages are still intact because I initially wasn't going to retune).

[MugelloB7RS4]

Quick update, I think I have sorted out the issue. I'm going to keep driving for a few days until I can be totally certain. I think what was happening was that the car was getting more air than it expected. The combination of the larger MAF housing in the Gruppe M and the removal of the intake flaps caused more air to go into the engine and at certain conditions the car didn't expect to see as much air at a specific throttle body position so it would set the fault.

Jake at JHM has been helpful is answering any questions I have on how the ECU works and helping me understand more than I did. Because of that among others, I will be getting the JHM tune.

Hopefully this helps anyone else that runs into the same issue.

[MugelloB7RS4]

sounds like a valid hypothesis, i'd swap in a stock airbox and see if that resolves the issue...

That's what seems to have worked.