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Author Topic: Audi A8 D3 4.0 TDI EDC16 limp mode problem  (Read 861 times)
ibizaCUPRA18t
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« on: March 01, 2018, 01:16:52 PM »

I have an Audi A8 4.0 TDI and have had some weird issues. With old motor it would go into limp mode after warmup with no turbo dtcs.

I changed the engine now I get left turbo controller short to plus. (I made a bridge from the Positive of the right controller and solved it). The car now goes great and goes into limp mode after few minutes. Turn on and off solves it and goes into limp mode again. Only DTCs are EGT sensor, however the sensor works and its also short to plus. So I change the loom.

I come to a conclusion that its the Loom and so I change the loom, after I change the loom the problem persist and this time I get a new problem, the Boost Sensor has an Implausinle signal. I change to a new sensor, same dtc now car is in full limp mode.

Can EGT sensors cause Limp Mode on diesels? Do you think I have a bad ECU which isn't sending signals properly? Because clearly my sensors are good!
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prj
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« Reply #1 on: March 01, 2018, 03:57:02 PM »

Sounds like bodging not fixing.

1. Turbo controller short to plus -> limp mode
2. EGT -> limp mode
3. Boost sensor - implausible signal -> limp mode

You need to bring the car to someone who knows a bit more about these than just hitting "read fault codes" button.
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ibizaCUPRA18t
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« Reply #2 on: March 02, 2018, 10:50:10 AM »

Asking a simple question does't mean I don't know what I'm talking about prj. Stop being short minded and arrogant. I was asking about this particular system. I own a 500m2 proffesional audi service shop, I'm not asking you how to do the repairs, I am JUST asking what could be the reason of unsolvable problems like this that occur with no reason. I am asking if the ecu could be bad, since I went through the repair procedures thoroughly (changed whole loom as well) and all I got was the same problem, plus a boost sensor code that wont go away... I didnt have these codes before I changed the engine, and I didnt change the electrical parts, only the engine!

Just asking for opinion, NOT proffesional advice lol dude
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prj
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« Reply #3 on: March 02, 2018, 10:52:28 AM »

So just get one or two spare ECU's and clone with BDM, if you exhausted all other options.
On dual ecu A8 the ECU is open to the elements, can easily have water ingress, especially if someone opened it before and didn't seal properly.

Did you actually measure continuity of the loom from sensor to the ECU? Did you check the ECU connectors?
Did you make sure that there is no shorted 5v voltage reference somewhere?

Any professional shop should be able to solve this quite easily. I know mine would.
« Last Edit: March 02, 2018, 10:55:04 AM by prj » Logged
ibizaCUPRA18t
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« Reply #4 on: March 02, 2018, 12:19:27 PM »

So just get one or two spare ECU's and clone with BDM, if you exhausted all other options.
On dual ecu A8 the ECU is open to the elements, can easily have water ingress, especially if someone opened it before and didn't seal properly.

Did you actually measure continuity of the loom from sensor to the ECU? Did you check the ECU connectors?
Did you make sure that there is no shorted 5v voltage reference somewhere?

Any professional shop should be able to solve this quite easily. I know mine would.

Yes sir! I unwrapped the whole loom did everything you mentioned as well. With the original loom I only had Turbo Controller Electrical Malfunction (no Positive) and EGT Sensor -> so I bridged a positive from the other controller one SOLVED (a bit ghetto move though.) Anyway; I test the car, runs great, however it goes into Mild Limp Mode due to the EGT Code not clearing. After checking sensor and wiring the fault still is present, so I change the whole loom in suspicion of it. THIS TIME: I get boost sensor code that won't fix at all, changed sensor etc PLUS I have the other problems I had with the old loom! So clearly its not a wiring issue.

Well I am happy that you would've solved this easily... but we've done everything, and maybe I just need to try changing the ECU that controls the respective sensors. However prj, I am kind of in denial here, an ECU doesn't cause these type of errors, ECUs usually work or they don't... right? And, also, problematic ECUs have intermittent problems. not constant ones like these.

Keep in mind: before I changed the engine, it had different issues, NOT these issues. We didn't damage anything in the swap process. This is the reason I am so frustrated with this car. Its just making-up problems. What would you do next?

I have another question as well: Are the dual-ECUs identical? They should be different though they have the same part # and have no markings like #1 or #2. Just asking if I change the ECUs to make sure I don't misplace them.
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prj
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« Reply #5 on: March 02, 2018, 02:16:49 PM »

ECU hardware is completely identical.
The flashable area (sgo) is also completely identical.
The only differences are in configuration (non-flashable area) and EEPROM.

As for errors - if inside ECU 5V supply has corrosion on it and is intermittent that can cause what you are describing.
Also it is possible that inside the ECU the pATM sensor is damaged, and because ECU assumes that sensor is always correct it gives an error for the pressure sensor instead.
You need to look at MVB's and look what values are doing.

EGT error - if the sensor wire been ever cut/bodged, it's done for. If you are 100% sure sensor, wiring is ok, then try different ECU.
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woj
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« Reply #6 on: March 02, 2018, 02:46:12 PM »

I am budging into something I have no clue about, no A8, TDI, twin ecus or anything. But, on the brand I am most familiar with, if there is more than one DTC after major work on the car, and especially three, that typically means something as simple as bad or missed earth somewhere. Just a thought...
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ibizaCUPRA18t
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« Reply #7 on: March 06, 2018, 09:20:02 AM »


As for errors - if inside ECU 5V supply has corrosion on it and is intermittent that can cause what you are describing.
Also it is possible that inside the ECU the pATM sensor is damaged, and because ECU assumes that sensor is always correct it gives an error for the pressure sensor instead.
You need to look at MVB's and look what values are doing.

EGT error - if the sensor wire been ever cut/bodged, it's done for. If you are 100% sure sensor, wiring is ok, then try different ECU.

I solved all other issues, now all I have is Exhaust Gas Temp Sensor 1 - Open or Short to Plus (under Engine II) which should be the right hand side egt sensor. I hope I am not changing the wrong one, would cost me some time... lets get to work I guess.
« Last Edit: March 06, 2018, 10:22:01 AM by Roni114 » Logged
prj
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« Reply #8 on: March 06, 2018, 12:49:51 PM »

I solved all other issues, now all I have is Exhaust Gas Temp Sensor 1 - Open or Short to Plus (under Engine II) which should be the right hand side egt sensor. I hope I am not changing the wrong one, would cost me some time... lets get to work I guess.
Bank 2 is always driver side.
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cherry
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« Reply #9 on: March 06, 2018, 12:59:26 PM »

Not in UK  Grin Grin Grin
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prj
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« Reply #10 on: March 06, 2018, 01:02:31 PM »

Not in UK  Grin Grin Grin
So if you are in UK invert the driver side on the correct side, and my point still stands.
Sorry, I don't do RHD.
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ibizaCUPRA18t
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« Reply #11 on: March 06, 2018, 02:11:57 PM »

So if you are in UK invert the driver side on the correct side, and my point still stands.
Sorry, I don't do RHD.

Let me get this straight, I am facing the engine from the front of the car. On my left hand side is Engine 1, right-hand side is Engine 2. So, if I get EGT Sensor code under Engine II ecu in VCDS that should mean I need to change the sensor to my right-hand side. Pretty much lol... let me not confuse myself.
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prj
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« Reply #12 on: March 06, 2018, 04:41:46 PM »

The right side of the car is on the left when you are facing the engine bay...........

Wow.
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