Glow plugs not available warning - but plugs test ok

[mi_piace]

Hi all,
my alfa 159 has recently started displaying the "Pre-Heating Glow Plugs not available" at start, so I took the car to the garage to get it fixed, and they confirmed that one of the plugs is not working and wanted ~ £150 to fix.

Before departing with my money I decided to check for myself, but all the glow plugs seem to function. I used a multimeter to check that the voltage between the +terminal and the top of the glow plug is ~12V.
I also removed the glow plug the garage told me was broken and tested that the resistance between the nut and the head is ~0.
Is there anything else that can be wrong with the plug that the above tests wouldn't reveal?

Is there anything else that could trigger the warning aside from the plugs themselves?

The guy from the garage was quite adamant that the warning was caused by one faulty plug.

Thanks,
Michele

[Fulvisti]

Have a search of the Alfaowner forum, I had the same trouble and remember finding the answer there. It was too long ago for me to remember exactly the resistance you should be looking for, but if you leave the glow plugs installed, disconnect the electrical connector and then measure the resistance from the top of the plug to the engine, it'll tell you which one is bad. They're cheap too from AlfaWorkshop.

[mi_piace]

I've rechecked them this morning, and 3 of them show a voltage of 12.34V between the +terminal and the top of the plug.
One of them measures 12.04V. That means the plug is still working but possibly not as well as the others.
Can the dashboard be so sensitive and report a problem for such small difference?

Michele

[mi_piace]

Hi all,
can anyone comment on whether the different voltage measured on one of the plugs could be enough to trigger the dashboard warning?
I wouldn't want to invest time and money replacing the plug if it's a red herring.

Thanks,
Michele

[t400ble]

How much are they new?

[mi_piace]

Around £20 new.
I am concerned about breaking the plug while trying to remove it. I know they can get stuck quite easily, so I'd rather not try if I don't have to