1998 Scenic 1.9DTi F9Q, where is pre-heat relay ? - Meganiacal
I have a 1998 Megane Scenic 1.9dti and a while ago, on the way to work, the temp gauge went crazy and stuck on max. Checked it over before going into work for the day and it all seemed fine, thought it must have been a dodgy gauge/sender. That evening, totally flat battery. RAC man came and eventually got enough juice into the battery to start it but it was draining continually. Pulled a fuse out and halted the drain, got home and checked what this fuse was and it was the diesel preheat circuit. Have been driving without the fuse in and it starts ok in the summer but now it is getting colder it won't! Keep having to put it in to start then pull it out, not very cool!
My problem is that I can't find the relay, I can find the preheat control unit but (according to Haynes) the relay is mounted separately nearby, but it isn't. I've traced the glowplug cables as best I can (with a clampmeter) and they seem to go to the back of the block, by the turbo).
I'm guessing that it must be a dodgy relay for it to be draining when the ignition is turned off and assume that this is affecting the temp gauge (I have changed the temp senders by the way). I reckon if it was the preheat control unit it would stop draining when the ignition is turned off?

Edited by Dynamic Dave on 11/12/2007 at 21:19

Renault Megane Scenic Diesel preheat - F9Q engine - RichardW
Could it simply be the temperature sensor that is as fault? It's gone open circuit, so the ECU thinks the engine is cold all the time, and is keeping the plugs on. CTS faults are not exactly unkown on Renaults (although usually on petrols).
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RichardW

Is it illogical? It must be Citroen....
Renault Megane Scenic Diesel preheat - F9Q engine - Altea Ego
There is probably also an earthing issue at work here. The full on temp guage is a sign of something finding earths through other sources other than the one designed (the big black one from engine to body)


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< Ulla>
Renault Megane Scenic Diesel preheat - F9Q engine - Meganiacal
Thanks both, as for the temp sensor, I have changed that already. I don't reckon it is an earth problem because for the first few minutes on start up the gauge stays on cold but as soon as it starts to warm up it goes straight to max.
Renault Megane Scenic Diesel preheat - F9Q engine - Screwloose
Megan

Find the brake fluid reservoir, then keep heading backwards, past the EGR solenoid with the rubber hoses and you'll find the glowplug relay hiding behind a tin shield.

If the fuse that you pull is a 40A maxi-blade, then be aware that it feeds more than the glow relay - it also feeds the coolant heater relays.
Scenic Diesel F9Q, where is pre-heat relay ? - Meganiacal
Thanks Screwloose, I've realised something, I was thinking the relay was separate to the ECU (as shown in Haynes) but after Googling the part number on the bit I had found I have found out that it is actually a solid state relay. So I guess it's not a case of cleaning the contacts but replacing the whole lot! Still not convinced it is this that is faulty because I don't see how the temp gauge would be affected.
Scenic Diesel F9Q, where is pre-heat relay ? - Screwloose
Megan

It is separate from the ECU. I think a lot more testing is required before you replace anything.
Scenic Diesel F9Q, where is pre-heat relay ? - Meganiacal
Yes, sorry, I meant separate to the Logic Control within the preheat unit but it isn't, it is a solid state switch within it. Now, looking at the wiring diagram, the fuse that I removed (70A) feeds only that and it does not go via the ignition switch, this would account for the battery draining whilst parked. So it is either the preheat control unit or its feed from the ECU, marvellous!
Scenic Diesel F9Q, where is pre-heat relay ? - Meganiacal
Here's a thing though, the glowplug warning light functions normally, whether the plugs are energised or not.
Scenic Diesel F9Q, where is pre-heat relay ? - raz69

I have the same problem with my scenic of the same year and engine. did you ever find out what the problem was?

thanks in advance

Scenic Diesel F9Q, where is pre-heat relay ? - osxgimp

I seem to have the same problem as well. The temp gauge just goes all the way up in about 1/10 second when it feels like it. Car stil runs nicely. I've found a few people with the problem on different forums but not final fixes?

 

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