# 2015 Ford Mustang - CEL comes and goes **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** ford\ **Created:** [February 28, 2025, 7:07am UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306 "2025-02-28T07:07:59Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![RoadMonger](https://avatars.discourse-cdn.com/v4/letter/r/b9e5f3/32.png) [@RoadMonger](https://community.cartalk.com/u/RoadMonger)\ **Post date:** [February 28, 2025, 7:08am UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/1 "2025-02-28T07:08:00Z")
I am getting an intermittent check engine light. The scan tool shows that the catalytic converter on the passenger side is operating 3 degrees too hot. I can reset the fault code and drive anywhere from 400 miles to 1000 miles before the check engine light comes on again. I was getting an engine misfire on cylinders 3 and 5. I put in new spark plugs and that stopped. The check engine light came on again. I replaced the upstream O2 sensor on the passenger side as the diagnostics showed it was faulty. While doing this I discovered the flange gasket on the converter was leaking. That was repaired. I still get the check engine light. And the scan tool shows the catalytic converter is running three degrees too hot. Just enough to cause a check engine light. My car is modified. I have the Airaid Cold Air Intake with resonator delete. The exhaust system from the cat back has an H pipe installed and muffler delete. Can these modifications cause the catalytic converter to run a little hot? I have no drivability issues. Fuel consumption is normal. The car starts fine. Idles fine. No problems accelerating or maintaining speed. ---
**Author:** ![It\_s-Me](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/it_s-me/32/12660_2.png) [@It\_s-Me](https://community.cartalk.com/u/It_s-Me)\ **Post date:** [February 28, 2025, 12:28pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/2 "2025-02-28T12:28:22Z")
What is the actual code # you are getting? Also how hot is 3 degrees to hot? Depending on engine load it can run anywhere from 500 to 1200 degrees, so 3 degrees isn’t going to set a check engine light. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [February 28, 2025, 8:31pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/3 "2025-02-28T20:31:09Z")
If you’re not having any drivability issues, then the problem might be a faulty EGT sensor. Tester ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [February 28, 2025, 9:01pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/4 "2025-02-28T21:01:42Z")
Actual codes for each of the things you mentioned as setting a code. In the form P1234, please. And is this an Ecoboost, V6 or V8… I assume V8 but you didn’t say. ---
**Author:** ![johnlump\_191311](https://avatars.discourse-cdn.com/v4/letter/j/47e85d/32.png) [@johnlump\_191311](https://community.cartalk.com/u/johnlump_191311)\ **Post date:** [March 4, 2025, 9:59pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/5 "2025-03-04T21:59:05Z")
Does the light come on in only certain circumstances such as when you were driving particularly hard? If that’s the case then I might be inclined to ignore it. But if you were just driving casually and it comes on then I’d suggest taking it in. ---
**Author:** ![RoadMonger](https://avatars.discourse-cdn.com/v4/letter/r/b9e5f3/32.png) [@RoadMonger](https://community.cartalk.com/u/RoadMonger)\ **Post date:** [March 6, 2025, 5:36pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/6 "2025-03-06T17:36:51Z")
I think I have an on-board monitor problem. The upper threshold for catalyst bank two keeps changing on the scan tool. ---
**Author:** ![RoadMonger](https://avatars.discourse-cdn.com/v4/letter/r/b9e5f3/32.png) [@RoadMonger](https://community.cartalk.com/u/RoadMonger)\ **Post date:** [March 6, 2025, 5:37pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/7 "2025-03-06T17:37:41Z")
I think it’s an on-board monitor problem. The max threshold keeps changing. ---
**Author:** ![RoadMonger](https://avatars.discourse-cdn.com/v4/letter/r/b9e5f3/32.png) [@RoadMonger](https://community.cartalk.com/u/RoadMonger)\ **Post date:** [March 6, 2025, 5:38pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/8 "2025-03-06T17:38:32Z")
It happens when I’m in sport mode. ---
**Author:** ![RoadMonger](https://avatars.discourse-cdn.com/v4/letter/r/b9e5f3/32.png) [@RoadMonger](https://community.cartalk.com/u/RoadMonger)\ **Post date:** [March 6, 2025, 5:40pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/9 "2025-03-06T17:40:28Z")
Don’t mind me. I’m learning how to reply to messages on this site. ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [March 6, 2025, 9:33pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/10 "2025-03-06T21:33:41Z")
No problem. You only have to reply once. You keep posting, and we’ll keep replying. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [March 7, 2025, 2:43am UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/11 "2025-03-07T02:43:40Z")
I will ask again… What are the codes you keep getting? Not your description, the actual number… in the form P1234. And tell us if this is a V6 or V8 ---
**Author:** ![johnlump\_191311](https://avatars.discourse-cdn.com/v4/letter/j/47e85d/32.png) [@johnlump\_191311](https://community.cartalk.com/u/johnlump_191311)\ **Post date:** [March 8, 2025, 4:01pm UTC](https://community.cartalk.com/t/2015-ford-mustang-cel-comes-and-goes/199306/12 "2025-03-08T16:01:33Z")
That’s interesting. Sport mode will map more aggressive air/fuel, spark timing, etc. But it shouldn’t by itself push it over the temp limit. So either the temp sensor is off spec or indeed you are getting too high of temps in sport mode. It’s just few degrees but will likely get worse. I’d be tempted to pay a shop to at least look at it and diagnose it. Focus on a speed shop where high performance drivers take their cars.