Has my check engine light been tuned out? [2004 5spd GT]


New Member
Feb 22, 2022
Hey, hope everyone is doing well. Got a couple questions that I've been trying to get answers for for awhile now. I own a 5spd '04 GT that I bought around 5 months ago.

My Mustang does not have cats or a check engine light. Are there any codes that are thrown up that could indicate that my check engine light for the cat delete was tuned out? I've gotten underneath the car before and the O2 sensors are present. Can't really tell if the previous owner used sensor spacers or some other method to trick the emissions system. I scanned the (non-CEL) codes on my car recently with a friend's handheld scan tool because I've been experiencing some misfire during idle. The codes that showed up were U1262 (SCP Data Link Fault) and PCM fault 1; nothing directly related to the O2 sensors.

Some additional (but possibly unrelated) context: my traction control (and I suspect my ABS) have never been working since I bought the car. The TCS button does not work and the indicator on the dash does not light up when I break loose in a corner/spin wheels. I'm curious if the codes I saw could lend any explanation for the lack of TCS/ABS and a CEL for my cats.

Thanks in advance for the help!
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These warning lights are still all bulbs in the gauge cluster. Given that it's been 18 years, it's possible that they are burned out, especially of those warning lights have been on for a significant amount of time.

For the CEL, turn the key to ON but do not start the car. Does the check engine light illuminate and turn off?

Same for the TCS/ABS light in the dash. Do they come on during bulb check? Are you sure your car has ABS/TC and someone didn't swap the switch in?

As for the U1262 code, that could be a possible PCM issue in itself.
Thanks for your response! My CEL bulb works fine. I blocked off my EGR valve to test if the diagnostics were working at all and the check engine light did light up. I'm pretty sure that ABS/TC were standard in my model year, I suspect they aren't working because of a wiring issue perhaps.

Regarding the U1262 code, I'm not sure how the PCM issue manifests itself with that code - I don't see anything awry with the car apart from the misfire which could quite likely be caused by a vacuum leak.

I'm mostly just trying to figure out why I'm not getting any codes for my cat delete.
Do you have MIL eliminators? These would also prevent the check engine light. They install online with the o2 sensors on the harness

Ford made ABS optional in 2004 on the GT. It was a $900 option. I bought one of these brand new so it’s something I’m pretty familiar with
Yeah Mustang5L5 is right... if there are MIL eliminators plugged into the sockets of the O2 sensors, that would stop the CEL from coming on. The PCM codes are weird. I guess it could be some sort of tune that was put into the PCM at one point to tune the cats out too. Don't know the inner workings of tuning that stuff out of the PCM but it could be possible. Good luck!