Ok, so I've done a lot of research and I am looking for some additional help. Hopefully one of you C5 electronics gurus can help me out. I have a 99 A4 coupe.
I am getting the dreaded Service TC/Service AH/Service ABS message. It seems to happen randomly and sometimes it triggers the Reduced Engine Power mode. I can usually just shut the car off and turn it back on and it is fine. Sometimes I have to clear the codes before it returns to normal. Here are my codes:

P1111HC- Intake Air Temperature Sensor circuit intermittent highvoltage
P0113HC- Intake Air Temperature Sensor circuit high voltage

The above two seem to be pretty regular, I can clear them and the check engine light goes out and it runs fine for a while then trips the codes and chk eng comes on again. I have replaced the IAT sensor to no avail and a visual inspection of the wiring turned up no frayed/broken wires. Thinking it might be the connector.

P0160C- HO2S Circuit Insufficient Activity bank 2 sensor 2
P0140C- HO2S Circuit Insufficient Activity bank 1 sensor 2

Rarely see the above two. I'm guessing they are oxygen sensor codes.
I do have long tubes with a tune done by a local Corvette shop.

P1221HC- Throttle Position Sensor 1-2 correlation

No clue on this one.

C1278H- TCS temporarily inhibited by PCM

Or this one.

Are all of these codes related? Maybe a ground issue? I cleaned all the grounds about six months back and it ran fine with no codes except for the IAT codes for a while, then the problem comes back and gets worse. Is there a particular ground I should be focusing on? Should I just cut the connectors and solder the wires to an eyelet? Any help you guys can provide would be greatly appreciated.

 

ttt

 

I'm interested too. I keep getting the P0160 C and P0153 HC codes more and more often. I also have long tubes and a tune.

 

May need new throttle body
read this link
http://www.gearchatter.com/viewtopic10439.php

Sounds like a bad connection at EBCM maybe ground connector on frame read the electrical sticky by Bill Curlee

Common codes with high flow cats.Your tuner should have been able to turn those off
without harming the cats

 

I too have long tubes on my car and was having some problems with the bank 2 sensors. Did some research and found that it was recommended that the bank 2 sensors should be disabled when running long tubes. Had this done and have not had a check engine light come on since.

 

I need to get my car tuning guru to fix this.

 

Thanks, good info on the TPS. I had a tune done when I put the headers on and I'm sure they tuned out the O2 sensors. I would think the code would be persistant if they didn't. I'm starting to think these are all related to a ground issue. Anyone know if the IAT sensor, EBCM, and O2 sensors share the same ground?

 

You need to fix your PCM problems. Here is some info on the C1278 code that will tell you why:

DTC C1278 TCS Temporarily Inhibited By PCM

Circuit Description
The PCM monitors various parameters and will not allow Traction Control/Active Handling (if equipped with RPO JL4) operation if any parameter falls beyond a predetermined value.

Conditions for Setting the DTC
A malfunction has been detected by the PCM. The PCM then causes TCS/Active Handling shutdown until the malfunction has been corrected.

Action Taken When the DTC Sets
This is a temporary operational malfunction.

TCS/Active Handling (if equipped with RPO JL4) are disabled.

Indicators that turn on: Car Icon (TCS indicator)
Messages displayed on the DIC: Service Traction System Service Active HNDLG (if equipped with RPO JL4)
Conditions for Clearing the DTC
Condition for DTC is no longer present and scan tool clear DTC function is used.
Fifty ignition cycles have passed with no DTCs detected.
Diagnostic Aids
This code is for information only. It indicates there are no problems in the ABS/TCS/Active Handling system, is used as an aid to the technician.

Bill