Crazy check engine light

[Vaughn-Vaughn]

Whenever I pull a sensor such as MAF or a coil the check engine light doesn’t come on. Instead the traction light comes on instead. However when I use a scanner a code pops up but no light.. when I turn the key to the on position I can see the check engine then but not when a senor is pulled. Why is this? Anyone else had this issue? Also I’m trying to fix a ruff idle and noticed this. Please help.

 

[Fless]

Tell us a bit more about your vehicle: make, model, year, engine, etc.

 

[OR VietVet]

Anytime you have an engine control function that is not connected or setting a CEL, the traction control light will come on as well. Has something to do with the system thinking that the traction control may not work as designed with an ECU problem, so the light comes on.

I am doing work on a 2008 Toyota 4Runner and it does the exact same thing.

 

[Doubeleive]

Whenever I pull a sensor such as MAF or a coil the check engine light doesn’t come on. Instead the traction light comes on instead. However when I use a scanner a code pops up but no light.. when I turn the key to the on position I can see the check engine then but not when a senor is pulled. Why is this? Anyone else had this issue? Also I’m trying to fix a ruff idle and noticed this. Please help.

usually it takes a run cycle for a cel to come on, it doesn't come on instantly like getting a doordash delivery.....
obd is different than other systems like the charging system, unplug the alternator and you will get a check charging system right away

 

[mattbta]

Is there electrical tape covering the money light?

 

[Vaughn-Vaughn]

Tell us a bit more about your vehicle: make, model, year, engine, etc.

2010 GMC Yukon Denali 6.2 L

 

[Vaughn-Vaughn]

Is there electrical tape covering the money light?

No sir

 

[mattbta]

No sir

Stranger things have happened is why I asked.

 

[Doubeleive]

AGAIN, the check engine light does not just come on because you unplugged something, it has a self checking system, it has to verify the problem before it lights up the lamp, this is why you see it with the scanner right away because it is pending.
your "rough idle" is apparently not enough to cause a CEL, you will need to troubleshoot a bit more and perform some basic maintenance such
as plugs, wires, air filter, clean the maf and throttle body, injector cleaner for a while or injector service, maybe even other things like a coil, or ground wire on the injector or coil harness but typically those will eventually throw a CEL
you could potentially even have internal engine problems.
it's going to take a little bit of investigation.

 

[Doubeleive]

if you want to see the cel on, then unplug the maf, map, coil, injector, etc and go drive it a while, then shut it off and start it back up, drive it a while again, shut it off and drive again at some point during those processes the cel will come on because the computer will confirm the problem.