ECU doesn't match chassis

[JLP]

Ordered a CAT, it came before the CEL bulb so I put it on before having a chance to pull codes.

Before having a chance to run it with CAT installed the bulb showed up. I'll add some notes about the bulb later.

Replace bulb, it works, stays on all the time. Find NAG switch and slide it. Code 12!

Run it and the very moment the idle dropped to 800 it started throwing 51. Drove just a bit and seemed to run just the same as it has been.

I had been through the EGR cleaning and testing except for cleaning of the MOD. Cleaned the MOD and drove it and it runs better, more pep and pulls better into higher RPM. I think maybe it is now advancing timing in the higher RPM range where it was not before. Before it was pretty flat above 3000, I didn't know any better. Short drive and short 800 RPM idle but no 51 so far.

I could not find a GE #18 bulb anywhere. Bulbtown had a CEC #18 with product code B18 that appeared to have the correct specs. It is physically larger but it fits. It glows just a bit dimmer than the other warning bulbs.

Thanks again for all the help! Hopefully 51 (and others) stay away!