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)

 

[Steve777]

Codes were: P0504 Brake Switch A/B Correlation (from when the car was in for an emission test), P1684 Battery was disconnected (battery was drained when a light was left on), and P0218 Transmission fluid over temp. Only one of possible concern is the P0218, not sure when that happened, and maybe it was due to the low batt, but am keeping an eye out for it.

I suppose the P0218 could have triggered a CEL, but it is odd that my reader did not find it, and equally add that it went away after being read at Autozone.

 

[Deb'nKJ]

If you're concerned about trans. temp, fit a gouge. Relying on there being an over-temp. code (which, of course, I never knew there was) isn't really practical.