segg

Sorry if this is wordy, wanted to try and provide as much information as I could.

I recently replaced spark plugs and 1 ignition coil in my 2010 Audi S5 4.2 V8 to attempt to remedy a cylinder 5 misfire. After completing the job I went for a drive to see how the car felt. Car drove fine. I parked the car at a store and went in to grab a few things. After coming back out the car would not start.

Errors.

When attempting to start the vehicle I was greeted with the following conditions and errors.

Conditions:

• Low hum, possibly fuel pump.
• No audible relay contact closure indicating starter relay had been energized.
• No audible starter sound or attempt to crank whatsoever.
• Vehicle behaved as if I turned the ignition on in accessory mode (even though my foot was firmly on the brake), e.g MMI booted, cluster lit up and needles swept, typical error light illumination in dash.

I immediately thought that I hadn't pressed on the brake firmly enough for the car to distinguish between ignition on and an engine start command. So I quickly took the key out and attempted again before noticing any errors.
After attempting to start the vehicle again to no avail, I observed the car run through a series of error messages on the dash that went as follows:
Errors, in order of appearance:

• ESP fault! See owner's manual >>
• PASSENGER AIRBAG OFF >>
• Ignition is on >> Service due ! >>
• Parking brake malfunction ! >>
• Tire pressure ! System malfunction >>
• Headlight range control defective ! >>
• Gearbox mal-function: you can continue driving (limited functionality) >>
• Sport differential: system fault >>

I was lost instantly. Very confused given the vehicle seemed completely normal on initial start before my store run, and the car did not exhibit issues while driving to the store.
What perplexed the most was the final error message Sport differential: system fault, because as far as I was aware, my car was not equipped with a sport differential. This made me think it must have been some sort of one off error that would not repeat upon a code clear or something of the sort. I had my code scanner in the vehicle with me and I proceeded to scan the cars OBD system to see if there was anything glaring, I received the following codes: U0100, and U0401.

The generic definitions for both codes related to some sort of loss in communication with the entire ECM. This scared me for a moment, but I thought maybe it just needed to be reset and everything would be back to normal! Wishful thinking...

I cleared the codes using my OBD reader and attempted to start the car again, same exact conditions/errors presented themselves. The next thing I thought was to disconnect the battery, hoping the harder reset of most of the equipment in the car would clear whatever magical issue I thought was present.

After letting the battery stay disconnected for 5-10 minutes I reconnected it and attempted to start the car once again.

Shockingly, the car started perfectly, with no issue cranking, and no errors on the dashboard whatsoever.

After a short burst of elation my heart dropped when I remembered the original conditions under which the car failed to start, that is, it was the second start attempt in which issues arose. After remembering this I figured I would do my due diligence and recreate the conditions by turning off the car (after letting it run for a bit) and restarting it.

To my dismay, all of the aforementioned issues and errors came forth again.

Now that the car was back at my house I began the frantic search for answers. I googled and searched a multitude of forums and found only one post with a somewhat similar issue, which was resolved by an ECM replacement.
Linked here: https://www.a5oc.com/threads/car-died-got-u0100-code.167780/

I couldn't bring myself to assume that the issue was just a "broken" ECM when the vehicle was running and driving earlier that day before I did the sparkplug job on it. Also in the post I found the issue did not arise after a repair so it wasn't an exact match to my situation.

So that brings us to now, before I pull out my multimeter and dive deep into electrical wiring diagrams, or spend hundreds or thousands of dollars on a new ECM, I fall to my knees and pray that someone on these forums has ANY experience or possible information/fixes related to this issue.

Thank you so much for taking the time just to read this post, hopefully we can resolve this together and help someone else in the future.

Alexkarayan

I just went through the same thing and had the battery replaced and spark plugs replaced, and the car died on the road and began to go into limp mode and only work after I turned it off and then back on.
Took it to the mechanic, and he could not find anything after a full diagnostic attempt and test drive.
went to pick it up that day and maybe 1 mile, and it happened all over again where it went into limp mode.
was able to bring the car back to the mechanic so they could see what was happening while it was running. They instructed me to turn it off and see if turning it back on, would do the trick, but it did not, and would never start up again.
we are now waiting for the mechanic to tell us what happened, but I think it’s something they did or were not smart enough to reset.
I don’t know if you can contact me directly, but I can keep you posted once I hear back from them.
From the picture, you can see that the screens were not working at all, and all the warning lights were on, and the windows would not go down, nor any blinkers work.
A very dangerous situation to be in this happens!

Limp mode





QUOTE=segg;25906498]Sorry if this is wordy, wanted to try and provide as much information as I could.

I recently replaced spark plugs and 1 ignition coil in my 2010 Audi S5 4.2 V8 to attempt to remedy a cylinder 5 misfire. After completing the job I went for a drive to see how the car felt. Car drove fine. I parked the car at a store and went in to grab a few things. After coming back out the car would not start.

Errors.

When attempting to start the vehicle I was greeted with the following conditions and errors.

Conditions:

• Low hum, possibly fuel pump.
• No audible relay contact closure indicating starter relay had been energized.
• No audible starter sound or attempt to crank whatsoever.
• Vehicle behaved as if I turned the ignition on in accessory mode (even though my foot was firmly on the brake), e.g MMI booted, cluster lit up and needles swept, typical error light illumination in dash.

I immediately thought that I hadn't pressed on the brake firmly enough for the car to distinguish between ignition on and an engine start command. So I quickly took the key out and attempted again before noticing any errors.
After attempting to start the vehicle again to no avail, I observed the car run through a series of error messages on the dash that went as follows:
Errors, in order of appearance:

• ESP fault! See owner's manual >>
• PASSENGER AIRBAG OFF >>
• Ignition is on >> Service due ! >>
• Parking brake malfunction ! >>
• Tire pressure ! System malfunction >>
• Headlight range control defective ! >>
• Gearbox mal-function: you can continue driving (limited functionality) >>
• Sport differential: system fault >>

I was lost instantly. Very confused given the vehicle seemed completely normal on initial start before my store run, and the car did not exhibit issues while driving to the store.
What perplexed the most was the final error message Sport differential: system fault, because as far as I was aware, my car was not equipped with a sport differential. This made me think it must have been some sort of one off error that would not repeat upon a code clear or something of the sort. I had my code scanner in the vehicle with me and I proceeded to scan the cars OBD system to see if there was anything glaring, I received the following codes: U0100, and U0401.

The generic definitions for both codes related to some sort of loss in communication with the entire ECM. This scared me for a moment, but I thought maybe it just needed to be reset and everything would be back to normal! Wishful thinking...

I cleared the codes using my OBD reader and attempted to start the car again, same exact conditions/errors presented themselves. The next thing I thought was to disconnect the battery, hoping the harder reset of most of the equipment in the car would clear whatever magical issue I thought was present.

After letting the battery stay disconnected for 5-10 minutes I reconnected it and attempted to start the car once again.

Shockingly, the car started perfectly, with no issue cranking, and no errors on the dashboard whatsoever.

After a short burst of elation my heart dropped when I remembered the original conditions under which the car failed to start, that is, it was the second start attempt in which issues arose. After remembering this I figured I would do my due diligence and recreate the conditions by turning off the car (after letting it run for a bit) and restarting it.

To my dismay, all of the aforementioned issues and errors came forth again.

Now that the car was back at my house I began the frantic search for answers. I googled and searched a multitude of forums and found only one post with a somewhat similar issue, which was resolved by an ECM replacement.
Linked here: https://www.a5oc.com/threads/car-die...0-code.167780/

I couldn't bring myself to assume that the issue was just a "broken" ECM when the vehicle was running and driving earlier that day before I did the sparkplug job on it. Also in the post I found the issue did not arise after a repair so it wasn't an exact match to my situation.

So that brings us to now, before I pull out my multimeter and dive deep into electrical wiring diagrams, or spend hundreds or thousands of dollars on a new ECM, I fall to my knees and pray that someone on these forums has ANY experience or possible information/fixes related to this issue.

Thank you so much for taking the time just to read this post, hopefully we can resolve this together and help someone else in the future.[/QUOTE]

Alexkarayan

My issue was that the alternator would work and then freeze.
ultimately it was the internals that would produce enough voltage .
it eventually got stuck and wouldn’t rotate and thats how the they found the issue