Multiple Engine Codes, Limp Mode

[TowMaudi]

I have a 07 A4 Quattro tiptronic with 115k miles and I recently changed the water pump +belt, cam follower, oil + filter, coolant flange + hoses + coolant temp sensor, thermostat, and oil filter housing. Today I gave it a drive to my bank about 3mins from my house and went I got back in to turn it on, it cranks and powers on but did not stay turned over. Waited a bit and it got on so I drove home and left it for a day come back to find it’s leaking coolant and now I have the codes P3081 and codes U0002, U0101. Following all this the wiring I believe for the connector that plugs into the CTS frayed out as it would throw me a high voltage circuit code, with the wires exposed to the heat it frayed out. Because of this the radiator fans will constantly spin and although the coolant temp does not overheat on the gauge, it does bounce around on the code side of it.I been meaning to change it but could not figure out the part number, any help is greatly appreciated. As I was lifting the car into ramps as well, it appears it has entered limp mode as I was stuck in 3rd gear getting up.


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[MSq5]

You may have to fix/replace the frayed wiring, but the P3081 is, indeed, for faulty coolant temperature sensor. Probably should replace it, too while repairing the wiring. I'd run a full VCDS scan again, now that it went into limp mode. You may get more codes.

The U codes suggest faulty CAN bus communication with the ECU and TCU, again a possible wiring problem. That may explain limp mode.

[TowMaudi]

You may have to fix/replace the frayed wiring, but the P3081 is, indeed, for faulty coolant temperature sensor. Probably should replace it, too while repairing the wiring. I'd run a full VCDS scan again, now that it went into limp mode. You may get more codes.

The U codes suggest faulty CAN bus communication with the ECU and TCU, again a possible wiring problem. That may explain limp mode.

Really? I replaced the oem coolant sensor once I got the p3081 code and a few weeks later it came up again, striked me as couldn’t be the sensor since it was new but maybe it was a defective, will order a new one to see if that makes difference but yea the wiring mess is something I thought I can fix by placing a new connector, I can’t find where the connection follows tho to replace the part. My theory is some of the leaking coolant must’ve messed up some wires for the TCM somewhere so I’ll give that a look later today


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[TowMaudi]

Update: Change the fuse for the radiator fan, gave the big wiring harness in the back a few good tugs and cleaned whatever connectors I can manage to pull off in the back, as well I pulled the cts connection a nice clean and tugging. Cleaned off the TCM module connector as well and seems to have gotten off limp mode, engine codes cleared and haven’t returned. I’ll give it a test drive later down the block but I am still leaking coolant, will probably use one of those UV kits to find it because I can’t tell where it’s leaking from but following it looks like it’s coming from around the oil cooler area, also a bit concerning is white vapors coming from exhaust, I do have a muffler delete on mines so sometimes it’s just water vapors steamed off but this seems whiter then usual might be coolant? Hopefully I don’t have a cracked head gasket but here’s to that


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[TowMaudi]

Never finished this write up, but in the end I took the car to the shop and all they had to do was splice the wires and create new connections and some new heat shrink to insulate it, haven’t had a problem with the cooling since, temp stays centered all the time now and doesn’t take long to get to temp and the fans turn off, my best guess to the coolant leak is the o-ring for the thermostat failed as I manage to see a very small glimpse of coolant running off, which would make sense as every time I refilled the coolant it would mostly drop to just under minimum level and would leak more.


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[mc_hotmail]

I recommend doing this as prevention: Extra heat shield on a BWT engine (https://www.audizine.com/forum/showthread.php/903314-Extra-heat-shield-on-a-BWT-engine)