Hello all - I have a check engine light on my 2008 GL320 CDI (80K Miles). Dealer tells me I need the Glow Plug Module (relay) replaced, but says MB also recommends changing all 12 Glow Plugs. The latter are quite expensive ($700+ in parts alone).

So my question is, is replacing the glow plugs really necessary? Or should I just replace the Module?

Thanks!

 

Glow plug controller diagnoses plugs every time it is started. One thing at s time Replace controller and it will tell you if you have bad plugs which you can address afterwards.

 

Of COURSE they are going to recommend replacing all the glo plugs! They are in business to make money and don't really care if they maximize your expenses or not. One thing at a time: 1- replace module, 2- if ANY of the glo plugs are indicated as out of spec, replace those only, wash, rinse and repeat at a later time. Bad glo plugs do NOT cause the module to go bad.

 

I was thinking of doing this as preventative maintenance but also don't want to throw money away for no reason. Seems like the consensus is to leave glow plugs and module alone until I have a problem?

 

I replaced only the module and it worked for me. I also wanted to replace the glo plugs at the same time until I found out the price and decided to just wait. That was the best thing. Been a year now and they are still fine. I would've been throwing away money.

 

Fourdiesel - how does this work? When a bad glow plug is indicated, do all have to be checked by inspection or does the system indicate specifically which of the 12 glow plugs are bad?

Also - can controller be replaced by a novice like myself? Are there instructions or a video posted by any chance?