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Discussion Starter #1 (Edited)
I'm getting "Permanent fault. Pre-heating relay circuit. Spark plugs permanently supplied." from PP2000 on my '02 Peugot 307 1.4HDI. Engine light on, and permanently in limp mode. It's been like that for about two months now - initially, it went off a few times and then came back, but it's all the time now.

Replaced the relay, no change. I can test it from within PP2000 and the new one clicks away happily, so seems fine.

From reading others' experience here, replacing the glow plugs is a messy and trouble prone business. Before jumping into that, I'm wondering would this be a worthwhile test:

- Get new plugs and (optionally) replacement cable harness
- Connect them to the relay instead of the existing set
- Check with PP2000 if the fault has gone away

I suggest this because PP2000 seems to pick up the fault, even before the engine turns over, and if replacing the glow plugs isn't going to sort it out, I'd rather find out now than later!

Worth trying? Anything else to check first?

As an aside, I had an accidental fill-up with petrol down the country about a year ago. Tank was drained, fuel filter replaced, and everything running fine since then, but would that have left any residual damage that might have contributed to the current problem?
 

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Yes, put a meter on the glowplugs and see if they are permanently supplied because if that was the case I would have expected them to have burnt out by now, you would also probably have experienced a very flat battery. Putting petrol in a diesel is more likely to damage the high pressure pump rather than anything else and certainly wouldn't contribute to your glow plug problem. Is that the exact descriptor as used in Peugeot Planet seems like something is missing.
 

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Discussion Starter #3
Yes, put a meter on the glowplugs and see if they are permanently supplied because if that was the case I would have expected them to have burnt out by now, you would also probably have experienced a very flat battery.
Thanks for the impressively quick reply! :)

I'll do a check later this evening and see what they read. They seem to be well buried under the air filter, unfortunately...
 

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Yea glowplugs aren't very accessible on a lot of diesels. Its worth doing a voltage check using PP to turn them on and off to make sure they aren't getting a positive feed from somewwhere. I am wondering if they are all open circuit and that is what is logging that fault code, it would be worth checking the resistance of the glowplugs after checking the relay works, just check the glowplugs as a whole no need to disconnect them at this point, make sure there is no voltage on them when you check their resistance, resistance should be less than 1 ohm, also would be good to check the resistance of this circuit from the relay output.
 

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Discussion Starter #6
So, I checked the resistance on the glow plugs from the relay output and they do indeed appear to be open circuit.

(To check, I disconnected the 8mm lead from the relay, and checked resistance between that and the -ve terminal on the battery.)

So, either the lead is faulty or the glow plugs themselves are open circuit - which I guess would be consistent with them burning out through being permanently supplied?

I also checked voltages on the relay: 12V in via 10mm lead, 12V out via 8mm lead, permanently, even after engine running for several minutes.

I disconnected the 5-pin header and checked the four wires on that as well: Yellow/green earth wire to center pin was 12V switched by ignition; to end pin was 10.7V, and to pin 4 (or 2) was 3.3V.

But perhaps the ECU provides a continuous feed if it's an open circuit?

I'll get PP2000 hooked up later and try switching the relay manually to see if the 8mm lead switches correctly when I do that.
 

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Yes it is better to use PP to switch the relay as modern diesels do use some post heat to keep emissions down so you can't always say that the glowplugs still being on after the engine is running is incorrect. Wiring diagram shows two lines from the engine ECU controlling the glow plug relay. It may simply be that the glow plugs have expired just through wear and tear and the open circuit is throwing up the fault code. It depends on how much of the circuit the ECU actually monitors. If switching the glowplug relay off and on with PP switches the glowplugs off and on voltage wise I would replace glowplugs, as they need replacing anyway and see if code clears, if it doesn't then the problem will probably lie in the wiring between the engine ECU and glow plug relay. Don't like that 3.3V sounds very suspicious, try measuring that pin with it plugged into the relay.
 

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I had the same fault on both the 307's I had. One was a 1.6 HDi 90 with the other being a 2.0 HDi 90. It never caused the anti pollution fault to be displayed or illuminated the EML. Generally, it only usually causes issues on cars with a DPF as more than one faulty glowplug will prevent a regeneration.
 

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Discussion Starter #9
Just to close this off:

I ran out of time (and courage!) to tinker with the glow plugs myself, so eventually handed it over to a local garage. They replaced the glow plugs without issue, fault cleared, and everything is now running fine again. It only cost €120 (£85) - €60 parts, €60 labour - which seemed extremely reasonable.

Our best theory is that the original fault was a bad relay which kept power permanently applied to the glow plugs. They then all burnt out in short order, leading to the permanent fault.

I must say, it's great to be out of limp mode - I can overtake with confidence again!
 

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Hi

Sorry to hijack thread, I've found this useful as it posts expected voltages and ohm rating for glow plugs/glow plug relay p1351 issue

I have a 307 with a fair few issues, that i'm trying to solve doing bit by bit.

So i've read around and trying to locate exactly where the fault would be, from what i've read its usually the plugs, just want to make sure..

reading this post, says that the plugs should be less than one ohm when checked for resistance. disconnecting the electric plug and testing the resistance between the two pins shows a reading of 200K ohms.

Also during ignition the glow plug connectors have a voltage of 1.25 v for all 4.

so i'm not sure if that's wrong or i am not doing it properly

Checking the relay,

there is voltage going to pin 4 at 12 ish volts, which is correct and there is a voltage from the diagnostic pin 3 at 4.7V and voltage from the ecu pin 8 at 9.7 volts.

I tried to test the relay like a conventional one, but also when reading several posts, where you need the diagnostic to trigger the relay. I dont have a pp2000 but have a high end diagnostic.

Would be cool to see if the numbers i have shown give a better direction, so i get fix the p1351 issue /depollution error

Cheers and appreciate the help!
 
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