Is this normal? Had a particularly cold morning (for here anyways), low 30's, and as usual, the GP light stayed on for a bit, once it went out, the car started fine. Put it in gear and started driving. About a minute later, the GP light comes back on, engine is running rough. Goes away on it's own few minutes later.

What does it mean when the GP light comes back on while driving?

TIA

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'98 E300 turbodiesel

Never heard of that one. Perhaps there is a fault with the GP relay.

Well i just had this happen to me.. searching through trying to find an answer.

Was driving for about 5 minutes and then the glow plug light came on and it seemed that the headlights dimmed to a lower level and stayed there.

Going to check the fuse and battery output tomorrow.

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'87 300D new to me
'85 300D Sold
'83 300cd Sold

I don't know if the IFI computer actuates the glow plug relay. It certainly monitors it, since you get a code if you start the car with cold plugs.

If the module uses a power wire (say, from the ignition switch or K40) to actuate it rather than the computer, the fault may lie there.

I would probably try another glow-plug relay first, if you don't have any other problems.

Although posting on a W210 thread, the OP has an older W124.

He ought to visit dieselgiant.com and follow the GP tutorial for the W123 to figure out whats up.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Well, it's not the OP with a 124, but I know what you mean. The problem is that I failed to note the date of said OP.

Guess I shoudl have said AOP (add on poster).

Yours was good advice for the 606.912 though.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

FYI, on the 606.910, if the glow light comes on after the engine has started and then goes off, that means a bad glow plug(s).