Pre Glow light illuminating after starting

Wishbone Ash

Hello lads,

Since yesterday, the pre glow light in my car is illuminating periodically while driving. It goes off as normal after a few seconds when starting but comes back on immediately afterwards and goes on and off intermittently while driving. Any ideas why?

Otherwise it's driving perfectly. Thanks.

(It's a 1998 MB E300 TD)

maidhc

That normally means an error has been logged by the ECU.

On a car of that age though it just might be something acting odd.

junkyard

Bad earth or a loose connection I'd say.

AMurphy

could be a faulty relay or glow plyg in that circuit. A faulty temp sensor or registering an ECU error code. Do you have a users/owners manual?.

crosstownk

Usually a sign of a fault in the diesel ECU. Do you notice any other symptoms in addition to the light?

AMurphy

Does this vehicle have a "Check Engine" light that is seperate from the Glow Plug light, or are the two integrated.

While ECU's do fail. it is rare and the last place to look, sensors are more prone to failure han ECU's

Wishbone Ash

Thanks for the replies lads.

AMurphy wrote:

could be a faulty relay or glow plyg in that circuit. A faulty temp sensor or registering an ECU error code. Do you have a users/owners manual?.

I had checked the owner's manual but it just says what the light is for -wait for it to go off etc. when starting but nothing about when it comes on again.

crosstownk wrote:

Do you notice any other symptoms in addition to the light?

No other symptoms - it's driving perferctly otherwise. It's done 127k miles. Next service due at 130k.

AMurphy wrote:

Does this vehicle have a "Check Engine" light that is seperate from the Glow Plug light

Don't think so but I'll check today.

bbability

Have the glow pplugs been changed in that car? A flashing glow plug light usually means a glow plug light is gone and considering the milage on the car.
Before you do that, check and make sure all your brake lights are working properly. The germans tend to put the brake light and/or door lights on the same circuit as the glow plugs. A visual check of the above might tell you something

Wishbone Ash

bbability wrote:

Have the glow pplugs been changed in that car?

Not during the three years that I have owned it. Not sure about previous owner.

A flashing glow plug light usually means a glow plug light is gone

It's not 'flashing'. It comes on for a minute or two and goes off for a while and back on again etc.

and considering the milage on the car.

130k miles would be low for a well maintained 3 litre diesel (IMO).

Before you do that, check and make sure all your brake lights are working properly.

Yes all working. (There are failed bulb indicators on dash) but I checked them manually also.

bbability

100k miles is the usual recommended interval to replace Glow Plugs. If they haven't been replaced maybe its time to...

Wishbone Ash

bbability wrote:

100k miles is the usual recommended interval to replace Glow Plugs. If they haven't been replaced maybe its time to...

Thanks for that bbability. I'll have a word with my mechanic.

crosstownk

bbability wrote:

100k miles is the usual recommended interval to replace Glow Plugs. If they haven't been replaced maybe its time to...

I've never heard of a replacement interval for glow plugs. Just replace them as necessary. If one is gone and the car has high mileage then maybe replace them all. But if they are in working order just leave them there.

Usually if a glow plug is faulty then you'll have difficulty starting. The more cylinders in the engine the less noticeable it will be. The warmer ambient temperatures we've been experiencing lately would also mask the hard start.

TBH, I'd let the problem 'develop' into something that will be easier to identify - but you always run the risk of getting stranded - usually at the worst time possible:rolleyes:

bbability

crosstownk wrote:

I've never heard of a replacement interval for glow plugs.

Sorry should have used the word "recommended" rather "interval". All in all PM is best (not private message but preventive maitenance)

Wishbone Ash

Thanks again lads.

The problem sees to have subsided somewhat today. It's coming on after starting for about 30 seconds and then remaining off for the rest of the journey.

AMurphy

bbability wrote:

...Before you do that, check and make sure all your brake lights are working properly. The germans tend to put the brake light and/or door lights on the same circuit as the glow plugs. A visual check of the above might tell you something

I have heard this reported before. but cannot remember what makes/models. But essentially the same story, ie, ABS or AirBag indicators were duplexed into lamps for totally unrelated functions, such as handbrake or Glow plugs.
Totally confusing and no explaination in the users manual. Which is why, it might be worth (necessary) checking what dash lamps represent which systems.

And depending on the answer to the above question, it could be anything. There are several conditions that light the ECU error lamp for brief periods. Examples being, loose gas caps, partially functioning ERG's, Failing O2 sensors.
Failing Thermostats causing the engine to run at low temperature, for too long.