Service engine soon light after trailer hitch wiring

[palmettosunshine]

Hi all,

As some of you know, I had a trailer hitch installed on my 2005 GXP along with wiring for the lights. Service engine light came on the next day, and a GM Tech2 scanner won't communicate with the car. The tech at the dealership where I work thinks there's a faulty connection somewhere that won't allow the scanner to communicate with the car. I know next to nothing about wiring, and have no idea what to look for when I pull it apart. I've checked the hot wire connection at the battery and taped up the connector block that was just flopping around loose under the seat. The other connections are at the left taillight and I haven't had a chance to pull it apart and check for anything obvious. Any thoughts would be greatly appreciated.

Oh, and if this weren't enough, when the hitch was installed, the exhaust had to be dropped at the rear to replace and reposition the hangers and during this process pulled the O2 sensor out from under the heat shield and the shield had cut the wires to the sensor and the heat shield was rubbing against the O2 sensor, making the most god awful noise you can imagine. $140 later, it was fixed at the dealership and the bill sent to the installer, who is making good on it.

I know I should just take it back to the installer and have him figure out where the fault is, but I'm just really not sure I trust him to be working on my car anymore at this point. Thanks.

[00Beast]

I HIGHLY doubt the wiring for your trailer lights are doing anything as far as this goes. I'd be looking at loose wiring under the dash.

[harofreak00]

Try to read the code read at a parts store first.

[palmettosunshine]

Haro,

Can't pull any codes because the scanner isn't communicating with the car.

[dpnewfie]

Read through this post:

viewtopic.php?f=21&t=15416

[harofreak00]

Haro,

Can't pull any codes because the scanner isn't communicating with the car.

I understand that the Tech2 isn't working, but you could try another scanner just to be sure.

[palmettosunshine]

Problem fixed. Called installer today, explained problem, he knew exactly what it was. He removed a self-resetting breaker and put an inline fuse in it's place. Went back to the dealer, hooked up the scanner,and voila! O2 sensor code. Cleared code, no more "service engine soon" light.

[CMNTMXR57]

I highly doubt it was the Tech2, if it was just used on another car...

[palmettosunshine]

Ok, so it wasn't that easy and I'm sorry I didn't post the solution sooner, as that drives me crazy when other people do it.

Service engine soon light came back on the next morning, couldn't afford to replace the front two O2 sensors right away so I just dealt with it for several months. Refused to fix it at the dealership where I work, and get 50% off labor, because they wouldn't discount the diagnostic charge. $70 bucks for the diagnostic, even though we knew what he problem was... Found a local shop with an ASE certified mechanic that used to work at my dealership who would do it for about half price. Bought the two O2 sensors, had them installed and the LIGHT STILL CAME BACK ON!!!!!!

Took it back to the mechanic the next morning and they were stumped at first. The mechanic slapped his forehead, pulled the fuse box cover and then the fuse......yep, a 10 cent fuse was the culprit the whole time. My dealership missed it and so did the indy mechanic at first. The good news is I was due for the O2 sensors anyway at 70K miles so it was no big deal. The bad news is I forgot the golden rule of wrenching: ALWAYS check the fuses first!

So, lest this happen to you, ALWAYS check the fuses first when you have a problem!

[CMNTMXR57]

See, it wasn't the T2. If you get a class 2 communications issue, it 110% of the time NOT the scan tool. Especially if the scan tool was used moments before on another vehicle.

The only time a vehicle communication issue will happen that is the T2's fault is if the VCI Module is chunked. You'll know this because any GM vehicle you plug it into you'll get this issue, and in some circumstances, may send the vehicle's PCM into freak out mode, illuminating every light on your dash, pegging all needles at max, engaging/disengaging your ABS and TCS, and a couple other things.

Yes, it's happened to me. :D