2.0L Diesel Vectra MIL new problem.

it may be something as simple as cold fuel or water in the sediment trap

Hi Tony,

Could be a problem with the glow plug control system. The plugs are actively controlled by the engine ECU during the warm-up phase (which you can see at night with the headlights or interior light on - these lights will go dim and bright as the engine is revved and the glow plugs are switched in and out). There is a seperate glow plug control unit, mounted in the relay box above the ABS unit.

When you get the codes read, the most common code seen relating to this fault is P1635 Glow device circuit general error. The first thing to check in this instance is the resistance of each glow plug - the control measures the current flow through each parallel pair of plugs and flags up an error if there is a discrepancy.

HTH

Anthony Remove eight from email to reply.

cut here

cut here

Your information is always spot on Anthony so I just need to check something in this information with you for my own understanding. At the moment I get this problem even though the engine and air temp may be at 10.0 deg C. As you once pointed out, the glowplugs are not switched in at these temps but are you saying the ECU checks even when the plugs are not in use?

I recently took all the glow plugs out and tested them individually directly across the battery. After 5 or 6 seconds, each one of them started to visibly glow dull red after which I disconnected them. So I am confident they are all functioning individually but, of course, that says nothing about the glow-plug-control unit you refer to or the connecting cables.

Is the unit itself a likely cause of the problem or just the plugs/leads.

Tony.

I have had a couple of occurences of faulty glow control units, but these are generally quite reliable. The glow control circuit was changed a couple of times to make use of different components and for different engines. On the earlier types there was a component that looked like a square relay with a black plastic cover in the relay box above the ABS unit. This contained two resistors which monitored the current flow through the glow plugs. I had a glow fault once which was caused by this part - MIL light coming on intermittently after start-up.

I was told by somebody previously that the glow plugs did not energise on the DTL/DTH engines until ambient temperature was around 4 deg. C. Having owned an Astra with a DTH engine for a few months now, I can state that this is not true. Just this morning the glow plug light came on for a few seconds even though the ambient temperature was 12 deg. C.

If possible, I would measure the resistance of each glow plug individually. Even though they glow when connected across a battery, there may be enough discrepancy in the resistance value to cause the engine ECU to bring the MIL on.

HTH

Anthony Remove eight from email to reply.

O.K. Anthony. I have had the good fortune to have the codes read today and, just as you suggested, it was indeed the glowplug control unit error. I will test the resistances as best I can. I could even get two glow plugs. Do you happen to know the pairing arrangement layout for the testing? E.g. is it the outer plugs paired or cylinders 1 & 2, and then 3 & 4? I would probably need to change a pair to effect a cure.

Anyway, since I think all the plugs are working, it seems not to be an urgent matter - just something I would like to rectify for my own satisfaction.

Thanks for everything in the advice department. Pity you don't write a service manual for these things!

Regards,

Tony.

Acting on your suggestion, I did bleed the drain tap on the fuel filter but it was as clean diesel as I could wish. It was a prudent first step as it only took a few minutes but it didn't cure the symptom.

I did later manage to get the codes read and it did turn out to be the glow plug control unit error - probably an unmatched pair as described by Anthony's reply.

So I will sort it out in due course as it isn't critical. I recently tested the plugs across the battery and am confident they do work although the resistances may be out of match by now.

As always, thanks for your advice. the older I get the more I realise I don't know! Tony.

You could either have a cylinder 1&2 and 3&4 glow plugs connected by an insulated bus-bar, or an individual connector to each plug, depending on the glow system on your vehicle. The connectors can be awkward to remove, there are two tabs that need to be pushed in on each side to release. Removing the plugs themselves can be a dodgy experience - some seem to be very tight in the head, leading to the hex shearing off the lower part the plug. Obviously a very bad situation to be in!!

No problem for the advice. I wonder how much different the Haynes manuals would be if they were written by somebody who had several years experience on the particular vehicle it was being written for??

Anthony Remove eight from email to reply

I did have them all out recently and tried them directly across the battery. They all started glowing after 5 or 6 seconds. So I should not have any problems removing them. The caps were difficult to remove until I caught on to the arrangement.

Tony.