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Added Prerunner lights now check engine light is on

Nero

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I installed 4 Prerunner lights to the grille of my JT. I connected the lights to the 15 amp Aux switch and grounded to body via one of the grounding bolts. Now the check engine light is on but the Prerunner lights work and the truck seems to be fine. I tried grounding to a different location but still having the same issue. Anyone have thoughts on what the issue could be?
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I'd guess you pulled a connector loose when you were in there.
 

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I installed 4 Prerunner lights to the grille of my JT. I connected the lights to the 15 amp Aux switch and grounded to body via one of the grounding bolts. Now the check engine light is on but the Prerunner lights work and the truck seems to be fine. I tried grounding to a different location but still having the same issue. Anyone have thoughts on what the issue could be?
I appreciate the fact that the light is called "MIL" in many troubleshooting books and service manuals because "check engine" is a very misleading term. It can mean a fair number of malfunctions aside from engine.

There's a lot of "what ifs" here and unknowns because we don't know what you took off, took out, removed or otherwise touched in the installation process. Could be a connection was pulled loose or a wire pinched when you put things together.
First thing I'd do is retrace your steps and see if it's possible that something was left loose or disconnected or that a wire was pinched somewhere if you used bolts/nuts or screws.
Connecting to an aux switch wire should be about the least risky thing one can do on these!

If you had a code reader of any sort - even just a bluetooth OBD adapter and free software on your phone it would help to know what the code is all about. The light on (Malfunction Indicator Lamp often called "check engine") means there's a code, meaning it doesn't like something and it could be 100% unrelated and coincidence that it happened now.
So - we're guessing in a sense.
 

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Arc, spark, fuse?
Yeah, but the odd parts is everything is working.
Unless he accidentally left a ground wire off when grounding his lights............ but that would be a lack of ground, not a fuse.
I did ask about pinched wire as I've caught a wire being pinched as I was bolting things back in place before - luckily saw it and got it out of the way.
 

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So what is the code(s) that is tripping the MIL?

We are not Carnac the Magnificent. Like mentioned, probably going to be something you touched but a code read will help narrow it down.
 
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Thanks for the replies. I don’t have a code reader but I will get one and update the thread. I did not see any thing spark when installing the lights, that would have been a red flag.

I took the grille off, wired and attached everything on it with a long lead. Then reinstalled the grille and fished the power and neutral to the aux switch wires. So there wasn’t a lot of actual wiring to do once the grille was reinstalled. I did have to do a few splices, I bought the lights off of Etsy, I think a few others on here have installed these. They come with a short lead and I added a 2 pin wire harness for each light in case I needed to remove something but I did check that the lights we working each time I made a splice with a 9 volt battery.
 

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So what is the code(s) that is tripping the MIL?

We are not Carnac the Magnificent. Like mentioned, probably going to be something you touched but a code read will help narrow it down.
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Update: I started the truck this morning and the check engine light did not come on.
 

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Update: I started the truck this morning and the check engine light did not come on.
That means that it saw a problem but no longer sees the problem.
For now, I'd let it ride.
But.......... I'd still look into getting an inexpensive bluetooth OBD adapter so you can at least use an app on your phone to check for codes. Anyone who does basic stuff should have that ability/tool. It can prove you didn't mess up, or show what you messed up if yo did mess up
 
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Thanks for the advice. I will get an OBD adapter, makes sense to have it.
 

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Any update on this? I did the same thing and got the same check engine light
 

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Thanks for the advice. I will get an OBD adapter, makes sense to have it.
Diesel or gas? If it is diesel, you might as well get a Scangauge which will not only read the codes, clear the codes but will give you valuable info on turbo temp, soot level, regen history and regen active status too. If gas, just get a regular OBD2 scanner.
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