Smart42

Glow plug relay issue, difficulty starting when cold.

15 posts in this topic

My 2006 Smart with 130.000 km is having issues starting when it is below -5C. Glow plugs changed 2 years ago (NGK), brand new battery and no error codes on my Scangauge. I turn the key, wait for the glow plug light to go out and start the car. It cranks fine, but has a hard time igniting the diesel and when it does it runs a bit rough for the first 20 seconds. However, if I plug the block heater in for 1 hour or the engine is still warm it fires up without any hesitation. This made a fuel delivery issue less likely IMHO. I had also noticed that I was not getting any extra heat anymore from the auxillary heaters when I slid the temperature lever all the way to the right. Based on this behavior I suspected an issue with the glow relay even though I did not have the P0380 code.

 

I had saved the old glow plugs and tested one with a battery and booster cables; it lit right up. My next step was to disconnect the glow plug lead from plug #3 and connect it to my test plug grounding it with a starter cable. I turned the key to position 2, the glow plug light came on and my test plug glowed bright red. I repeated the same procedure with plug #1 and #2 and got nothing, no heat whatsoever. I disconnected the connector from the glow plug relay on the right hand subframe and tested the glow plug leads for connectivity. They were all good. Based on these findings I believe my relay is defective.

 

I removed the glow plug relay. This can be done from the engine bay if you have nimble hands. Disconnect the 2 connectors and use an E10 Torx bit for the 2 bolts securing the unit to the subframe. The factory has used blue Loctite on them so it takes a bit of effort.

The glow plug leads are marked G1, G2, G3 and the +12V is a wide spade connector.

 

This Bosch 0 281 003 021 relay has 4 Philips screws on the corners. Remove them and you can see the inside. It consists of a metal base plate with, what I believe, are Mosfet transisitors and a circuit board on top.The glow plug connector part has 3 Mosfets; I assume one per plug. Access to the Mosfets is difficult as it would require desoldering all the connections of the circuit board.

 

My questions for the board:

 

-1 Why do I not get a P0380 or other code even though 2 glow plugs are not getting power?

 

-2 Do you agree that the relay is defective or are there any other parts I need to rule out?

 

-3  Is it possible to test the Mosfets without desoldering them from the circuit board?

 

-4 Has anyone ever successfully replaced faulty Mosfets on this relay?

 

-5 Any leads for a reasonably priced new relay?

 

 

 

 

 

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This is brilliant. I didn't realize it was the same controller for the AUX heat and glow plugs. I've been having a hard cold start problem since I bought the car and the icon for the aux heater is on all the time even when it should be off. I'm changing my controller tonight to see if it changes anything...

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Your problem is very similar to what mine had...

 

Start fine, but run very rough for s short time and perfectly after.... 

 

The alternator finaly get stuck after sitting in the driveway for couple weeks and i sold it..

 

 

 

Edited by David_18

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My alternator seems to be working fine; Scangauge shows voltage of 14 volts as soon as engine is running. Also, a bad alternator does not explain why 2 out of 3 glowplugs are not getting any power and the third works as designed..

 

Back on topic: does anyone has the exact wiring diagram for the glow plug relay? I was wondering if the SAM switches each glowplug individually. If that is the case the problem could still be in the SAM.

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You won't get any wiring diagram for the glow plug controller.  SAM is not involved at all with glow plugs, their control is by engine ECU and glow plug controller.

 

I have replaced MOSFET transistors on other makes of glow plug controllers but not on this one.  You can check if they are working when soldered in.  Just Google.

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Auxiliary electric heater not working could be faulty outside temperature sensor or faulty coolant temperature sensor.  Can you confirm if these are indicating correctly?

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Thanks for the speedy reply and Merry Christmas to all of you :D

 

Do we know if the ECU switches each glow plug individually or leaves it to glow plug controller? I find it interesting that I do not get a P0380 error code unless I pull the connector of the last operational plug. I wonder how the ECU determines that there is a problem with the glow plugs?

 

I am not an expert in electronics but will use my Google Fu to see if I can figure out how to test the transistors. The problem that I see is that removing the top circuit board to get at the Mosfets will be a royal PIA.

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Just now, tolsen said:

Auxiliary electric heater not working could be faulty outside temperature sensor or faulty coolant temperature sensor.  Can you confirm if these are indicating correctly?

 

Yes, both appear to work fine. Reported outside temp is more or less environment temp and coolant temp is +/- environment temp on start up and quickly rises as engine heats up.

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Changed my controller, still have both problems. :(

I was going to buy a new one, but mines new now...very few things haven't been replaced. lol

Keep feeding the parts monster...

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3 minutes ago, kdubya said:

Changed my controller, still have both problems. :(

 

 

That was quick. Did you test to see if your glow plugs light up when you turn the key?

Did you replace it with a new controller or another used one?

 

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(I'm working a night shift in an office :), or as I call it, work on my car time) A used one from a parts car that had low km. I didn't have the glow plugs removed. I figured this was the wrong place to snap one off. I've replaced the aux heater before too, along with glow plugs, injectors, alternator, starter, ground wires, fuel pump relay was done, crank position sensor, and countless other things. I figure the cars need a new wiring harness after 10 years.

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Except a multimeter, a general knowhow of how to fault find a wiring harness, and total motivation to start it :)

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