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post #1 of 5 Old 05-23-2008, 08:28 AM Thread Starter
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CEL and Codes U0101 and P0571... what did I do?

Alright, first the let me set the stage to the problem... I had hardwired my radar detector into the review mirror using a hardwire kit similar to the invisicord. Anyway, when I first wired it, I used a voltmeter to find a ground and +12v wires in the mirror. I connected everything and when I plugged the radar in, it powered on and then went into a "self calibration" mode. I turned the car off, and then on again and same thing occured with the radar, but then it powered off, and I couldn't get it to turn again. I rechecked the wires I jumped to and learned that the ground wire I used was grounded only while the car was off, however, when started, was no longer grounded... (that's weird). Anyway, I found a constant ground and everything with the radar works fine now.

Ok, now heres my issue. After that occurred, I started my car up to take a drive and a my check engine light came on. I did the key dance and it showed codes U0101 - Lost Communication with TCM and P0571-BRAKE SWITCH 1 PERFORMANCE. The CEL turned off after I had three drive cycles, but I'm not sure why those codes would have thrown, or what they mean exactly. I thought maybe I shorted something by not having a correct ground at first and a fuse blew in my brake lights, but they seem to work fine. It seems like the two events were interconnected, but I'm not sure how... especially with the TCM??? Any ideas on what I did, what it is, or if it's related to the miswiring in the mirror or not?

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post #2 of 5 Old 05-23-2008, 09:05 AM
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ok 571 . . .

571 applies because you have two brake switches on the car. one near the pedal and another that applies based on fluid movement in the abs module.
A 571 hits when one switch gets hit and the other doesnt. Like it sees a signal from the brake switch but doesnt see any fluid being moved in the module, so it gets confused and sets the code.
This could have happened any number of ways but i see it more than nought when people try to add radios or something aftermarket and they use a low quality test light or dvom. The low quality ones will actually allow some current flow through them even in voltage settings. What this does is basically you (while probing around) could have quickly completed a ground circuit a different direction by making the ground go through your test light/dvom instead of allowing it to be grounded by the module> remember on this car is over 35 modules all of which control every electrical switch in the car.

the tcm communication should only have popped if you pulled the ground to a module, much like fuse pulling. Remeber all modules on this car communicate with each other so when you pull the radio out, over 30 codes get seen in the car for lost communication with the radio module
Now why did it only show tcm???? Thats because your evic only displays codes from the pcm. most people think it displays all codes but each module in the car has its own list of codes. The evic only shows pcm codes however so you pulling a ground took away communication (especially within 24 hours of key off which is when all the modules do communication tests) from many modules . The rear view mirror is a module, so is the radio, sunroof motor, everything.
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post #3 of 5 Old 05-23-2008, 09:29 AM Thread Starter
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Thanks wicked... I could be possible that I reversed the ground while probing, or also maybe could have been caused by unconnecting the wiring harness from the mirror? It seems like I just did something to confuse it and it threw the CEL, but no harm was done? No need to take it to the dealer to have it checked then? I hope...

Last edited by pikapp; 05-23-2008 at 09:39 AM.
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post #4 of 5 Old 05-23-2008, 12:08 PM
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pikapp, next time you want to add an electrical item/component to the canbus circuit, get the wiring diagram for the circuit you will tapping into so you won't have to probe, and before you start, disconnect the negative battery cable and allow a few minutes before to start working on it. This will prevent the weirdness you saw.
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post #5 of 5 Old 05-23-2008, 08:31 PM
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yes by reversing the ground path will throw the comms out of wack,and please diconnect your battery before doing any electrical hacking...just becuase the key is out doesnt mean the circuts in the car are dead. Be carefull in the electrical wiring in these cars..very touchy. i dont think you did any damage..if so i think you would have noticed it still throwing codes...the TCM code you got was probly just the first comm that was lost during that cycle and thus showed up first..but if you could look at the data logger in the car there was at least 10 more lost comm to modules in the system..you just got to see the first one. you should be fine but if your uncomfortable,then bring it in and let the Stealership give it a check up.

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