Expert: Sean Halliday - 3/18/2009

Question
Hi,
The CES light is on on my 2000 Maxima. When I check for a code, it shows up as "No Codes". The first time it happened, I reset it, and it came back - same thing. My mechanic got the same results and suggested taking it to Nissan. Nissan told me that their diagnostic readers have more capabilities, and ultimately said that I needed a new catalytic converter. I had them replace it ($1300), and about a 2 - 3 months later the CES light is on again, but still no codes.

My questions are:
1. What capabilities do the dealer's have that are different from reading the codes?
2. What recommendations do you have for fixing the problem?
3. Have you ever heard of this before?

Any help you can provide on this is greatly appreciated.

Thanks in advance.
Rick

Answer
These are called ghost codes.Check engine on but no codes stored in the PROM.(Memory).It can be a faulty pcm,rare but possible.If you clear the code how long does it take to come back on?The main diagnostic advantage the dealer has is,a major piece of scan equipment designed solely for Nissan,it gets into all aspects of the engine,abs,srs,and transmission as the hand held units will only read codes.These machines the dealer has can reset all codes and scan individual systems.Such as,rpm,signal output,airbags,transmission behaviour and abs sensor condition.A major piece of hardware but cost a lot,20k at least.Best thing is go back and have them look again,they missed something.Worst scenario is change the pcm(computor).With a used one from the junkyard.This a rare thing but i have seen it.Sometimes it can be a delayed action and the code will appear eventually if you drive it for 3-4 days.Did the dealer tell you how he came to find the fault in the cat with no code?This is a problem i have seen with nissan for some reason unknown,they do this and i have a sentra code o2 sensor which is good, but still the light stays on.So,its a faulty pcm which is too much cost to fix and the car drives fine so i clear the light for smog and it stays on.Im betting its the same with yours,pcm fault.See if the dealer agrees.