Throwing P0135 And P0155 After H-pipe Install

So I had a shop install an o/r H-pipe on my 96 gt Automatic recently. I didn't have any MIL eliminators installed, because I have a Bama handheld tuner from American Muscle, and figured it would be able to turn off the rear 02 sensor codes, and save me some money.

Well the tuner looks to have turned off the rear sensors just fine, but soon after the install and applying the tune I received p0135 and p0155 which appears to be front 02 sensor codes (bank 1 sensor 1 and bank 2 sensor 1) for a heater circuit malfunction.

Has anyone run into this issue or anything similar before or have any advice or thoughts? The car seems to be running same as always so far, no misfires or anything... I know they had to do a little bending in order to get around some stuff because the car's an automatic... not sure that would have anything to do with anything though. I also think I might be hearing a little bit of rattling when I put the car in reverse to leave my driveway, but it sound fine after that.

madams74 said:

Could very easily be your O2's needing replaced. I have a Bassani X with High Flow Cats. I was getting the same codes but only for passenger side. I replaced that sensor and the code never came back. I had tried to clear the code a few times and it would take about 5 minutes before it would come back on. Then it seemed like every time I started the car the code was back immediately then. Once I replaced the O2, all was well after I cleared it. I just used a Bosch sensor. The real kicker is that I only have 26,000 miles on the car. 2002 Mustang GT. You would think the sensor would be like new......................

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Hmm, okay, guess that's what I'll have to do. Just seems odd it happened right after getting the midpipe installed. Thanks for taking the time to reply.