Michael Severin

Purchased a 2001 Z28 Camaro. 5.7 Liter LS1 Coupe.

Exhaust had been butchered and Cat's cut off. My check engine light is on account of the O2 sensor which hasn't been a bother, but I heard from a friend who has similar 01 Z28 that when the Check Engine light is on, the car is running in "Emergency Mode" That it hurts gas mileage and performance.

Is this true? Getting ready to install a new SLP Loudmouth Exhaust on this car. "No Cats" Is it easy to override and O2 sensor?

Any information would be greatly appreciated.

Thanks!

Injuneer

Depends which sensor the code if for. If it's for an after-cat sensor, has no measurable effect on anything. If it's a pre-cat sensor, your running 1/2 of your engine blind, and there is no way for the PCM to adjust the fuel to maintain the target A/F ratio.

In any case, it's never in "Emergency Mode". In the absence of some sensors, the PCM uses a default routine to provide the data it needs. It will no longer be "optimal", but it shouldn't be described as "emergency". Each code has different meaning and a different degree of impact on the way the engine runs.

There is a condition known as "limp mode", and that is what happens when the PCM basically loses most communication with the engine. Few people have ever actually experienced that level of operation.

What is the specific code - I have the GM lists for all years 93-02?

Michael Severin

I haven't purchased a code reader yet. I only knew the check engine light was on, on account of the Cats being removed. What do I need to do?

Thanks!

Injuneer

You need to scan it. I can give you a link to free 98-02 OBD-2 scanning software, with GM Enhanced Parameters:

Free OBD2 scanner software - Firebird Nation

You will need to get a cable. OR, if all you are trying to do is pull a code, the cheapest OBD-2 code readers and phone apps can do it.

Since you seem certain that the SES light is on because of the cats being deleted, those codes (one for each bank of the engine) would be set by the absence of the after-cat O2 sensors, or by the absence of the cats. You an have the codes "programmed out" of the PCM, or you could find O2 "sims" to replace the O2 sensors.

Michael Severin

Thanks a million! I will do this.