No glow plug light - '99 E300 - Car runs fine
 

Hey all,

Have been running with a CEL on for several months, code is P0380 (glow plug relay). That being said, the preglow system works great -- car starts promptly at temps as low as 10 ºF. All six GP's check good resistance and are receiving power, else I would definitely get misfires on startup.

My main concern is that the glow plug light never turns on. The lamp itself is fine. Can a fault with the instrument cluster (causing the lamp not to turn on) trigger the CEL?

Thanks!

No, cluster has nothing to do with CEL.

P0380 is a circut fault/engine cranked on cold GP's. Will reset itself after 3 cold/hot/cold run cycles if doesnt reoccur during that time. If the CEL is constantly lit, a fault is reoccuring.

If relay powers GP's you might want to see if it cuts out too early after starting. Should stay on for ~2 min after a cold start. If so, need to determine if is relay or K40.

Terry -- the CEL is constantly lit, still with P0380.

I've had the dealership scan the ECU with Star Diagnostic, which returned some pretty interesting results. The code definitely points to the relay ("module", in their terms, as it contains more than just a relay), and the wiring diagram they pulled up indicated an issue with the part of the module that controls GP's #5-#6. However, the code had existed for an undetermined amount of time -- this is unusual. On their recommendation, I replaced the module with a new part .... same code and CEL remains on. Thus, the fault is (and was) definitely not in the relay/module.

Terry, I know you have some experience with the K40. As far as I know, mine is original. How could it failing affect the ECU in such a way to cause a CEL? Is there anything related to the K40 that would explain why the GP light never illuminates?

Any help is much appreciated!