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Thread: First Major problem, limp mode and unable to read codes

  1. #1
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    Nov 2016
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    Default First Major problem, limp mode and unable to read codes

    This one has me a little puzzled, so a little background. 2009.5 g8 gt. I've been running this setup for about 3 years now with almost 40k miles on it on the setup and about 145k on the car. Small tsp cam, and supporting valve train mods, ported heads, Magnuson 2300 7 - 8lbs of boost, meth injection, stock trans, and all stock electronics.

    Was driving at around 60 with cruise control set, drops throttle response, cruise control, and starts down shifting, once it dropped to 3rd I put it into neutral because I didn't want it to try 1st at 60. Wouldn't go back into gear, and (as figured) turning the car off it wouldn't turn back on and I have an accompanying Christmas tree on the cluster. Before cutting the car off there was no misfire and it idled perfectly normal.

    I disconnected the battery and started to look for wiring issues, fuses, or anything obvious, my heater core hoses were running up again the main plug behind the fuse box. I moved the hoses away from those wires, checked to see if they were tight going into the back of the plug (pictured) and they all seemed good. More poking around I didn't find anything, hooked battery back up, and the car fired up and wasn't in limp more anymore, although check engine, see dealer, traction, abs, and brakes lights were on. Still ended up trailering it since I wasn't near the house. Drove on and off trailer, sat for 3 days, fired up today with all the lights, immediately back into limp mode, and now will not start at all once again.

    Here is the main problem, used a code reader and HP tuners and it would not read codes or clear codes, it cannot establish communication. After playing with the code reader and that harness connector I got it to work but it had 4 codes, only 1 of which I was able to get before it kicked me out, U0073. I'm suspecting the plug(s) pictured but I cannot find a part number for them and according to the dealer I cannot get them unless I get a whole new harness. Wanted to know if anyone knows the name / part number of these plugs if they can be separately purchased, or and possible suggestions on what this issue can be if it isn't related to this harness.


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