HORRIBLE electrical problem - glow plugs / Module. Calling all clued up folk...

[dann2707]

So I am having an issue with my mk4 1.5 dci clio. This thread is going to be pretty indepth tracing wires so not your usual "change this" thread.

Specifically when its freezing the car struggles to start and can sometimes take 7 attempts and I am getting a glow plug open circuit fault P0670.

So far I have changed the glow plugs and the module for new units...

I will show the wiring diagram so you can see the circuit which i've annotated but will also include a blank version too at the bottom.

On the module the pins are as follows:

1 - To glow plug
2 - To glow plug
3 - Signal Wire
4 - 12V incoming feed
5 - Ground (Switched ??????)
6 - To glow plug
7 - To glow plug
8 - Diagnostic wire

The glow plugs are earthed through the engine block.

I will talk through what I have done so far to diagnose... All things i've tested with a glow lamp to put load on the wires. (Anything in brackets shows what i'm testing)
Below are numbered points nothing to do with pin outs:

1 - Checked the incoming 12v feed from fuse box to glow plug module.. all okay and getting 12v. (confirm any breaks in cable)
2 - Loaded up signal wire from the ECU to the glow plug module, all okay (confirm any breaks in the cable)
3 - Loaded the diagnostic wire from ECU to the glow plug module... all okay (confirm any breaks in cable)
4 - The purple wire below goes to the camshaft position sensor, this looks to be a switched earth as its not currently an earth when probing it? This has confused me. Why would it have a switched earth AND a signal wire? Is this normal in auto electrics? I load tested that wire too, from the ECU to the glow plug module and not breaks in the wire but this one has me baffled a bit. This wire is proper thick coming out the module too, but then goes to a really thin ecu wire???? Thats not earthed as standard? To me that doesn't make sense but does stack up with the wiring diagram.
4 - Checked the earth from engine block to chassis, loaded up and all okay (check condition of ground)
5 - Despite glow plug module getting 12v feed, i've removed the main 70a fuse and cleaned it all up on the contacts (confirm good connection)
6 - Put a DC current clamp meter on glow plug wire AND main bulk of all glow plug wires and can confirm no current at all during starting.
7 - I have not checked the glow plug individual cables from the module. I just thought about this whilst having my tea but very unlikely as I have already clamp tested the bulk of the wires and absolutely nothing.


I feel pretty f**king defeated I won't lie and can't think what else would be causing this issue.

For what its worth, it comes up as a pending fault, and then turns to a full blown fault.

If anyone has any ideas on what to try next i'd be all open to any suggestions please! I feel like i've been really thorough but i'm clearly still missing something...

More of a close up without my drawings.

 

[Scrooge]

It’s been a long time since I played with a dci but usually even glow plug fault and slow starts are injector issues.

Before you go too mad with everything else I’d check they’re all good

 

[Brigsy]

Stinks of airleak at filter/primer or injector on its way. Do a leakoff test

 

[dann2707]

Cheers chaps, I've got a leak off test kit to try next but avoided it because of the glow plug fault code and how they're not heating at all.

It only struggles when its freezing too so all things to me are pointing to glow plugs.

 

[npt]

Presume all codes have been cleared after fitting new glow plugs, if all are dead when cranking then its likely a grounding issue from the ecu, got to be sure all plugs are good and no broken wires...wiggle wiggle wiggle, renaults are shite, sell it 😂

 

[Scrooge]

My little brother drove his dci everyday with no glowpugs connected for about 5 years. It always started ok apart from the two times the injectors went

 

[Brigsy]

Both of mine have glowplug faults stored. Defo none working on my blue one, fires off no issue -5 temps.

Log fuel pressure when cranking on diagnostics.

 

[npt]

It should really struggle if not impossible to start if no glow plugs are working at that temps

 

[dann2707]

I've got a picoscope kit I bought years ago and never used so just ordered some probes for it so I should be able to log a lot of things now at a decent frequency. My handheld reader is pretty basic.

I'll get a leak off test done ASAP too, probably tomorrow!

Whilst I agree it definitely could be injectors I can't leave that it only happens when it's freezing and I'm definitely getting no heat to the plugs

 

[Flob]

I can't help because diesels are the devils work.

What is the function of pin k3 on the ecu. The pin which is connected to both camshaft position sensor and the glow plug module? Is this supposed to be the signal line from the cam sensor or is this sensor 5v/gnd?

The Cam sensor likely is a hall effect and has 3 pins. Signal (square wave), power (5v), GND. It could be that the glow plug module looks at this square wave out of the sensor as a way to know the engine is running. This would also explain why you don't see power or gnd on that wire.

Do you have an oscilloscope to probe pins 8 and 3 on the module? EDIT* just read about your picoscope. From what I read the module needs a wake up signal from the ecu, I would guess this comes on pin3?

 

[Flob]

Have you checked the timing by the way bud? @Speedo Gonzales has the specs.

 

[Speedo Gonzales]

Has anyone consulted @Trainerbrow ?

He might have an idea

 

[dann2707]

I can't help because diesels are the devils work.

What is the function of pin k3 on the ecu. The pin which is connected to both camshaft position sensor and the glow plug module? Is this supposed to be the signal line from the cam sensor or is this sensor 5v/gnd?

The Cam sensor likely is a hall effect and has 3 pins. Signal (square wave), power (5v), GND. It could be that the glow plug module looks at this square wave out of the sensor as a way to know the engine is running. This would also explain why you don't see power or gnd on that wire.

Do you have an oscilloscope to probe pins 8 and 3 on the module? EDIT* just read about your picoscope. From what I read the module needs a wake up signal from the ecu, I would guess this comes on pin3?

So according to Chatgpt it's a clean reference ground that's going to the camshaft sensor mate.

The other two wires appear to be a signal wire and then the reference checking wire bud.

 

[dann2707]

Pin 8 = control
Pin 3 = diagnostics
Pin 5 = cylinder sensor

According to official wiring diagram

So that sounds plausible what you just said @Flob about it detecting engine moving.

If that's not getting a signal from camshaft sensor I wonder if that could be related.

 

[Flob]

Pin 8 = control
Pin 3 = diagnostics
Pin 5 = cylinder sensor

According to official wiring diagram

So that sounds plausible what you just said @Flob about it detecting engine moving.

If that's not getting a signal from camshaft sensor I wonder if that could be related.

Keep in mind I made that up, its a complete guess.

I would carry on once you have your probes. But I wouldn't rule out the fact that the car might have two issues. The glow plugs being one and an injector going bad. With either working fully seems they should still start alright going by Scrooge and Brigsy's messages above.

PS - if my guess is anywhere near correct then its more likely the module uses the signal from the cam sensor to turn off plugs once engine is running. Why it would need to do this when it has a control line from the ecu I don't know - so equally it could be a reference ground. Would be good to see a list of ecu pin functions of you have access to that to confirm that pin k3 is expecting.

 

[Flob]

Small amount of googling suggests that Black is ground, Green/White is signal and Green brown (Yellow in my screen grab) is a 5V reference

that will be easy to confirm by probing the cam position sensor, should be able to find 5v and gnd then the last one (which I think goes to the glow module) does look to be the 5v square wave signal out of the hall effect cam sensor.

 

[Flob]

If its a new glow plug module, new glow plugs and you have tested the continuity of all the wires you have to then start to suspect the ecu may have a fault or the new glow plug module is wrong. Your scope will likely answer that question.

 

[npt]

Ground it using an old bit of wire and see if it gets power through the clamp, just give it a quick buzz, if it works then thats the issue