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How to - Repairing the Glow Plug Relay on a W203 220CDI

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by Dunkuk, Nov 24, 2013.

  1. Dunkuk

    Dunkuk Guest

    This is my first post on here but I thought I'ld make it a useful one. This shows how to fix your glow plug relay.

    The relay is situated in front of the battery and is easy to access, it has 1 thick 12v lead going to it held on by a nut (10mm I think) and one big 4 way connector taking the 12v off to the plugs, and one little connector taking the control signal from the cars computer.

    My glow plug light was on when I bought the car. Taking the plug off the front of the glow plug relay revealed 4 connectors, one going to each glow plug. By measuring the resistance from each of these 4 connectors to earth (cylinder head) I found that all measured around 1-2 ohms, which is what they should be.

    I then connected a headlamp bulb to each of the outputs of the relay in turn, the 4 male spade connector parts within the large connector. So one side of the bulb to the relay, the other to earth. Then turning the ignition on the bulb lit up (taking the place of the glow plug). 3 of the pins made the bulb light, one did not. So the relay must be faulty I thought.

    Looking at replacements, a 2nd hand one on ebay costs about £30, a new one from GSF car parts costs £80. Quite a lot, so I thought I would try repairing the relay.

    The relay is glued shut with a hard black material. Too hard to cut with a knife. I drilled this out with a pillar drill and a 2.5mm bit working my way all the way round. I then joined the holes up with a stanley knife and a small chisel for the harder to cut bits. I then prised it apart with a chisel.

    This revealed that a "fusable link" had blown, basically a fuse made of a thin bit of metal. Photo 1.

    I soldered on a 30amp blade fuse (the glow plugs take 11A to 16A on my car so 30A should be plenty). Photo 2.

    At this point I tested it in the car before I glued it back together, and it worked fine.

    I removed any small bits of plastic left over from cutting to make sure they don't jam up the relay, then glued it all back together with Gorilla glue (foaming wood glue), although I would imagine hot melt glue, expoxy or silicon sealant would work. Just be careful not to get any glue on the relay.

    Once dried I put it back in the car and it all works fine and the relay light is off.

    I hope this is helpful to someone.

    By the way my local specialist garage would have replaced the glow plug first (as the computer cant tell the difference between a blown fuse and a blown glow plug, then replaced the relay, probably looking at £200 or so of parts + labour with genuine MB parts.)
     

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    Last edited by a moderator: Nov 24, 2013
    domwild likes this.
  2. turbopete

    turbopete Senior Member

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    very nice job! you could, of course, have fed the wires through small holes in the outer casing, and had the fuses EXTERNAL so that if they ever do blow again, theyre very easily replaced! you could also have made provisions for the other 3 fusible links (ie soldered wires into place,) ready to fit a fuse if ever another link blows!
     
  3. roofless

    roofless Senior Member

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    What is it with MB owners & drills.
     
  4. turbopete

    turbopete Senior Member

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    i believe that, in this case, it was justified (personally, id have used a hacksaw)
     
  5. roofless

    roofless Senior Member

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    I've opened a couple with a blade then silicone seal after repair.
    A hacksaw blade would do the job
     
  6. OP
    Dunkuk

    Dunkuk Guest

    I would love to know why it blew in the first place, I'm hoping it won't happen again. I think the previous owner had a really bad mechanic as it looks like the glow plug has been replaced but this was left as it is, not working.
     
  7. roofless

    roofless Senior Member

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    The fault code would point to glow plug 4 ect even on Star
    So the last guy prob just changed the plug.
    To be fair it could be a faulty plug causing the damage to
    The relay & that's why it's best to fix both
     
  8. hmang

    hmang Senior Member

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    is 30amp about right for the fuse ?
     
  9. turbopete

    turbopete Senior Member

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    i think personally, id have gone for something a little smaller. perhaps 20A or even 15A
     
  10. OP
    Dunkuk

    Dunkuk Guest

    I think the plug had been changed but perhaps they stopped at that due to the price of the relay.
    Re the 30A fuse, I measured the current draw, 2 of my plugs took 11amps each and the other 2 took 17 amps and that's not accounting for any surge at switch on. Of course it's up to you what you put in, just be aware if it blows you will have to do the whole thing again!
     
    Last edited by a moderator: Nov 25, 2013
  11. kimi

    kimi New Member

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    Glow plug module repair

    Well done sir, It's nice to see there are others who have the skills to try and repair things rather than just blindly junk the old and fit new ! Like a lot of garages do these days. Plus the bonus is a big saving in cash !:D:D
     
  12. davidsl500

    davidsl500 Senior Member

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    30A is about right as you would normally use a fuse of double the normal current draw for the circuit. I presume the old glow plug caused a direct short circuit and blew the fuse, the glow plug was replaced but the relay was not due to cost..

    It's nice to see things getting repaired rather than this throwaway society . so long as the cost makes sense of course!
     
  13. EmilysDad

    EmilysDad Senior Member

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    If there is a new improved part available, do you really want your garage to spend time trying to repair a part rather than replace? In the case of this glow plug relay, by the time he's spent an hour repairing, the labour costs could have gone towards the new one ...... I'm all for trying to fix stuff, but sometimes, new, is the way to go.
     
    Last edited: May 8, 2016
  14. Frontstep

    Frontstep Senior Member

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    Its the sort of thing you do as a diy-er a garage usually does not understandably have the inclination as the price is too near for the risk of future failure.
     
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  15. domwild

    domwild Active Member

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    You are a genius. Many thanks for that.
     
  16. Umarnewcastle

    Umarnewcastle Senior Member

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    i did change glow plugs and repair relay but still car not start but if i spray quick start spray it starts straight away any idea what it can be

    regards
     
  17. umblecumbuz

    umblecumbuz Senior Member

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    Old thread, still useful.

    Scant info Umarnewcastle.
    It could be any number of things, but your 203 model can get air in the fuel lines when the O-ring seals harden and leak - well-known problem. That would explain why your engine fires and keeps running when you use Easistart.
    That's just one random thought, out of several possibilities.
     
  18. Umarnewcastle

    Umarnewcastle Senior Member

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    thanks for reply

    but some time it starts fine i did change o rings
     
  19. brianbrian

    brianbrian Senior Member

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    Our time for repare on a car cost nothing, if the garage repare parts it would cost an arm and a leg for there time. So they change the part.
     
  20. ajlsl600

    ajlsl600 Senior Member

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    well done that man.. i will try to remember that, hindsight is a great thing, but with the benefit of. i would also have tried to organise an external fuse for all 4 plugs or a secure way to seal/ reopen the relay
     

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