2004 Gt Auto With Engine Codes After Full Exhaust Install...any Advice?

mlb585

New Member
May 22, 2010
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Hello everyone. I just had my local mustang speed shot install a set of JBA shorty headers, shorty h-pipe (with MIL eliminators from American Muscle) and flowmaster catback. The shop told me that one side of the rear o2 harness was very short (maybe since it’s automatic) and had to be extended for the h-pipe install. Everything sounded great and went well until the drive home where about 15 minutes into the drive I got the dreaded ‘check engine’ light. I ran codes at Advanced Auto Parts and codes P0054 and P0442 popped up. I know that P0054 is related to one of the rear o2 sensors…not sure if it’s from the guy rewiring the o2 extension or the MIL’s just not working right. I’m not sure where the P0442 came from because that indicates a small leak in the EVAP system. Not sure where to go from here as the car seems to run fine (idles slightly lower that before though). Any help or thoughts on this would be greatly appreciated as I don’t have much knowledge on 4.6 mustangs. Thanks
 
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P0054 is an O2 heater code. For the passenger side downstream O2. It could be something as simple as a poor connection.

As for the P0442 code. Check your gas cap.
 
+1 on pulling your battery cable & see if the codes go away, your computer has some new things it needs to learn with a full exhaust. And if you haven't already crawl under there & make sure that none of the wires ended up getting cooked on your exhaust after the shop did its work. I'd be taking a close look at the wiring done to extend one of the harnesses.
 
I purchased a cheap little blue-tooth adapter for my odb2 to use with an application "OBD check" from my android to allow me to run codes on the go. My point is... easier to do a hard reset by pressing a button on your phone than disconnecting the battery. Maybe I am just lazy. Pretty cool little app though. However the torque and hp readings are just plain comical.
 
Thanks guys for the info. I reset the codes (battery disconnect procedure - I desperately need to get a cheap code scanner) and let the car idle for about 10 minutes and took it for a drive. Everything seemed great but 10 minutes into the drive both codes came back. Driveability is the same though.

I will look into the o2 issue as that may take me a little time/effort to figure it out. When I bought the car it came with a locking gas cap that never worked quite right. I'll replace it with a standard one and see if that takes care of the code.

One other thing, I always noticed that my car idled fairly low when I put the car in drive. It idles around 550-600 when sitting at a light in drive or around 700 in park... is that normal? If not, how can I adjust the idle or is there something else going wrong here?