Last night my 06 Z51 gave a CEL. When I read the trouble code it showed a p0430 ( Catalyst System efficiency below threshold (Bank 2)). The car is running LT Headers and hi flow cats with all 4 O2 sensors installed and the rears were turned off when it was tuned after header install three years ago. I have had no CELs whatsoever since the tune. I understand this code usually indicates a bad rear O2 sensor on the passenger side, or a bad catalytic converter, by comparing the signals between front and rear sensors and if they are not within an allowable range p0430 is triggered.

My question is since the rear O2 sensor is turned off how can this code indicate a possible bad sensor. Is it possible that it is indicating a bad front sensor instead, since a dead front sensor would show the same signal as the rear sensor which is turned off and therefore out of range? Anybody with a knowledge of how this code can be generated with a rear sensor turned off would be appreciated.

At this point, I cleared the code and will see if it comes on again when I drive the car again. I also will jack the car up and inspect the O2 sensor electrical leads to make sure they are in place and not burned as well as make sure none of the sensors are loose.

Advice and help from someone with smarts about this problem please.

 

Depending on how they got turned off, it may still be looking for them and if it gets an error you will get a code.

Example, I had a Predator in 2007 (2006 Z51) and then you could turn off the rear o2 sensors (can't do that now), so I did not install the rear o2s and got a code. I plugged them in and the code went away despite them being turned off. Car is now tuned with HP Tuners, no sensors and no codes.

 

I don't know how many ways they can be turned off. Mine were turned off during a dyno tune by the tuner. Your experience makes me wonder if even though they are turned off the ecm recognizes whether they are electrically functional. Maybe electrical continuity is monitored. If so, then I guess it's possible to recognize a bad sensor which has an open circuit.

 

That is exactly what happen when I turned them off with the Predator.

Not sure how the tuner turns them off, but are not present at all, and no codes, so I would call your tuner.

 

That's my next step.

 

Follow up: After clearing the p0430 code, checking for burned leads or loose sensors (nothing found), I drove the car about 70 miles today mostly at high freeway speeds and no code reappeared. Will keep looking for it to come on again, but so far so good.

 

Great! Now you need to go buy a lottery ticket!