Glow plug light

[acf8181]

Car is starting and running perfectly.....but upon starting glow plug light stays on for a minute or so, and then randomly every now and again it comes on when driving once car is warm for a minute or so!

Could this be a sign of the control unit failing?

and should i just continue to ignore it as car is running perfectly?!

 

[acf8181]

Oh, probably should say its a W203 C220 CDI Sports Coupe

 

[zipdip]

Well looks like you need to put a diagnostic scanner on it,I would suspect it is just a glow plug cost around £15 ,maybe consider buying a dedicated mercedes scanner like iCarsoft it will save you lots of money pointing out whats gone wrong.

 

[classiccarzone]

It is usually the sign that a heater plug has expired. I would not get too excited about it but it may lead to the other heater plugs expiring.
Very often it is not a very easy job to remove the heater plug.
Many break in the head when they are being extracted.

 

[DSM10000]

The car will continue to run fine after it starts, glow plugs play no part in the running of the car just aid with starting.

The car will check all components regularly and if a plug value is out of range then the light can be illuminated.

 

[whitenemesis]

There's also an after-glow function depending on engine coolant temps.

Task
Improving the warming-up characteristics
Preventing blue exhaust after a cold start .
Improving smooth engine running after a cold start
Stabilizing the cold starting speed

Function
After engine start the CDI control unit (N3/9) determines the
preglowing time in line with the coolant temperature.
If no signal is received from the coolant temperature sensor (B11/4), afterglowing is activated for 30 s.

 

[DSM10000]

There's also an after-glow function depending on engine coolant temps.

Task
Improving the warming-up characteristics
Preventing blue exhaust after a cold start .
Improving smooth engine running after a cold start
Stabilizing the cold starting speed

Function
After engine start the CDI control unit (N3/9) determines the
preglowing time in line with the coolant temperature.
If no signal is received from the coolant temperature sensor (B11/4), afterglowing is activated for 30 s.

Interesting!

It would not explain the light illuminating when warm though as the OP states sometimes occurs?

Also, when used to aid the above conditions would it re- illuminate the glow plug light?

 

[whitenemesis]

Usually when one or more glowplugs go down the light goes out as normal when the engine starts, then within 60sec, comes back on for 30-40 sec then goes out and stays off until the next ignition cycle.
In normal operation the light goes off after the pre-glow and engine start and stays off even during the after-glow function.

 

[topdown]

Usually when one or more glowplugs go down the light goes out as normal when the engine starts, then within 60sec, comes back on for 30-40 sec then goes out and stays off until the next ignition cycle.
In normal operation the light goes off after the pre-glow and engine start and stays off even during the after-glow function.

 

[acf8181]

There's also an after-glow function depending on engine coolant temps.

Task
Improving the warming-up characteristics
Preventing blue exhaust after a cold start .
Improving smooth engine running after a cold start
Stabilizing the cold starting speed

Function
After engine start the CDI control unit (N3/9) determines the
preglowing time in line with the coolant temperature.
If no signal is received from the coolant temperature sensor (B11/4), afterglowing is activated for 30 s.

So could potentially be a coolant temp sensors issue?.....have noticed it seeming to indicate the cars a bit colder than expected on the guage, and have a few low rev unsmooothness issues (could just be hoping theyre related of course)