Will a CEL affect performance at all (limp mode)

What causes the ECU to go into limp mode?

 

LOL, it depends on what the CEL is. Many, many are not performance, or even engine related.

Limp mode is a safe mode to protect the car. It happens when something fails that can blow the engine, or very expensive parts. Usually it's a big leak some where, a sensor out of spec, like the cam sensor. The SAP, or AC will not cause limp mode. It has to be something engine running related.

 

Great guys thanks for the help!

I'll check all of that out this weekend hopefully. I appreciate it!

 

I had it happen a few times when I went into limp mode with no CEL lighting up the dash. The only way I found out what the problem was, I had to scan the car and sure enough there was a DTC stored but the CEL remained off.