Audi s8 2007 u0115

A8 All/ S8 All
#1

It keeps saying lost communication with pcm. It seems to only happen under semi heavy load. I cant really throttle the car hard the traction light will come on and it’ll misfire and start like stuttering. I did change some relays. Im really not too sure whats causing it. It also throws like every code o2 sensor speed sensor evap solenoid thingy when I put it under semi heavy load. I did change some relays.

Im not sure if it’s related but the alternator is kind of running on the low side like a 13.2 or sometimes go up to 14.2

Im going to check my grounds around the bay. Is there any particular ones I should look for?

#2

Dude that sucks. Thats sounding like a grounding or short issue. The wire harness on these cars tend to get exposed wires quite easy. See if you can drill down on what’s going on

#3

i’m leaning towards the alternator i already ordered another one so we will see what happens. i’m currently about to pull the motor on the s6 i just need to lower it and unhook the shifter pretty much. i plan on gutting the cats on that car at that point and i’m not sure if you remember i was having weird starter issue so i’m going to change that as well since i’m changing the trans.

also on unrelated news on the s8 bank 1 senor 1 the o2 was saying heater issue and running horrible so i changed it with 17328 which is for the s6 and it seems to be working. when i was first changing the engine on the s8 i accidentally ordered s6 02 sensors for the car and got stuck with them.

#4

Should be the same. I’ve used old S8 02s on a newer year 5.2 without issues.

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#5

Changed the alternator. Didn’t resolve the u0115 but it did bring the voltage up a bit. Shortly after I realized the postive wire on the battery was super hot and it burned me so I replaced it with 0 guage wire. It did fix that and the car did get better i am able to throttle it way more without it doing it. All the the codes I keep getting are pointing towards the slave computer. Im wondering at this point if the computer got messed up from the high resistance in the postive?

Also I noticed at alternator is 14.4 and when postive goes into car by the relay panel on passenger side it drops to 14.0. Maybe thats also a factor im not really sure to be honest lol