Engine Lite On but no Codes

[Steve777]

Have a strange situation. CEL (engine lite) came on on my 06 CRD the other day, no issues running so when I got home tried to pull codes. My code reader (an Innova 3160rs, a decent one) could not find any codes??? Drove down to the local Autozone and had them pull the codes (they also use an Innova reader), and they found some old codes stored, nothing that serious. Odd thing is after they pulled the codes the CEL went away. I asked them about it and they say they never clear codes???

So a couple of puzzles here. Why would old stored codes suddenly turn on the CEL when my reader couldn't pull them, and why would it go off later when those codes were read but not cleared. Is the computer going wonky? Anyone seen this sort of thing before.

 

[KJowner]

Very strange, sometimes you get odd issues when the battery is on its way out, the PCI BUS runs at higher voltage than modern CAN BUS so it's very susceptible to voltage dips especially cold starting a diesel.
My father in law doesn't use his much, when he starts getting issues it's time to put the battery on charge because he doesn't do enough miles to charge it!

 

[Deb'nKJ]

The CEL's out, that's all that matters (as you haven't mentioned any faults/symptoms)