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After installing an aftermarket radio into my car it threw a code for a bad O2 sensor. I took my car to a shop to get the code read. The code reader would not connect to the ECU in order to read the code. We thought it was the code reader itself. After trying 7 different code readers that wouldnt connect to the ECU i realized there was a problem with the connection in the car. I searched around for a solution to the problem and the main thing that came up was the installation on an aftermarket radio could interfere with the connection to the ECU. Nobody really explained why it interfered with the connection. So i took my car to New German Performance Racing to find the problem. They had a simple solution for a big problem. There is a orange wire on the stock harness usually labeled the "Illumni" wire. The wire is not connected to anything so the ECU can get a connection to any code reader or computer. What does that wire have anything to do with the ECU connection? I have no idea. But when you go and get an aftermarket radio installed somewhere 99% of the time they will connect the orange " Ilummni" wire on the stock harness to the orange "Illumni" wire on the aftermarket wire harness. The connection to the aftermarket radio somehow interfers with the ECU connection. The wire must be disconnected in order to allow connection to the ECU. Problem solved!

I havent figured out why the wire interferes with the connection but i will keep looking. Let me know if this has helped your problem.
 
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