The glow plug light stays on while the engine is running. I had a car electrics guy check it out and after two hours of looking for the relay, disconnected it and then re connected it worked for about an hour before it came back on and stayed on. Is there anyone who could tell me if this is a warning of a serious problem or just a falty relay.

- (#15003) Gar, 19 Jan 05 16:50

Year? Model?

Jeez, where to start. There's a couple of different kinds of glow system, there are normally *two* relays, and any misconnection of the wires around the inlet manifold can cause weird bugs...
- (#15003) David Miller, 20 Jan 05 01:42

On Townaces the glow plug light is driven direct from the glow plug timer unit and should go out before you start the engine and stay out. Sounds as if the wiring has been messed with, but probably not in the area of the two glow plug relays.

See discussion and wiring diagram at Ace Answers > Fuel System > Glow Plugs

- (#15003) Dave Mason (Sussex), 20 Jan 05 03:42

Thanks for the responce lads. Sorry for not giving more detail, the model is Super Extra 4WD and the year is 1993, as to the messing with the wiring, didnt happen. My main worry is that this is a warning light of somthing which needs to be repaired and not just a nusance light because when the lead is disconnected & reconnected to the relay it works properly but after about 20 min it stays on again. Thanks again for the info I will try both.

- (#15003) gar, 21 Jan 05 01:18

It isn't a warning light per se. The light should come on when you turn the ignition on and go out when it is the recommended point at which you fire the engine. The light going out coincides with the voltage drop from about 10.5 to 7V ie. when the plugs have done their stuff and warmed the air in the chambers. At a guess I would say the wiring is dodgy as already indicated or the relay could be playing up. If you get the RM025E engine manual from your Toyota dealer, it explains how to test the system components. To save time check your e-mail, I've sent you the scanned section.

- (#15003) Ian Dunse (Derbs), 21 Jan 05 01:39

I'm guessing here, but it's a long shot, that there might be a problem with the EGR system, or possibly the throttle position sensor. 1993 should be a facelift model, and I wonder if the "emissions computer" as they call it (in the B pillar) has some diagnostic functionality that earlier ones didnt.

But first check would be whether one or more of the glowplugs is burnt out. Earlier models have a "current sensor" that doesn't appear to do anything, I wonder if it is enabled in later models to indicate a glowplug failure. It's normal in todays diesels to have this kinda monitoring- VW TDIs can even tell you which individual plug is faulty...

To check, you'd either need to remove the busbar and meter each GP, or find someone with a high current ammeter to check the draw of the full set in-situ.

On balance, I'd go with a duff glowplug.

- (#15003) David Miller, 21 Jan 05 01:48

Yes, the "current sensor" is a bit of a mystery. It's shown in RM025E but does not appear to be present in 1991 Townaces. It's logical that it's purpose would be for the Glow Plug Timer Unit to detect a failed glowplug and signal that with the glow plug light.

Does anyone know how much current these glow plugs take?

A small query on what Ian said ... normally the light goes out to say "ready to start". Yes. But do the volts drop from 10.5V to 7V at that point or after the engine starts when the Glow Plug Timer Unit gets a signal from the secondary output of the alternator?

- (#15003) Dave Mason (Sussex), 21 Jan 05 03:42

Volts drop as the light goes out. Nothing to do with engine starting.

- (#15003) Ian Dunse (Derbs), 21 Jan 05 06:45

About 8A per plug, generally...

- (#15003) David Miller, 21 Jan 05 10:16

One of the few differences between Ian's Townace and mine is that my glow plug system has a buzzer (are any two Aces the same!?).

I checked this morning. After 5s the light goes out but the volts remain high then reduce about 0.5s after I start the engine. However if I delay starting, another 5s after the light goes out a buzzer sounds and the voltage reduces.

It seems to me that the two-voltage system is therefore not to provide the anti-stall over-run at a gentle lower-than-normal voltage. Rather, it is to provide a an initial burst at higher-than-normal voltage to get the plugs hot more quickly. Probably someone can interpret the glow plug spec in this respect.

Does anyone else have this glow-burst-end warning buzzer?
- (#15003) Dave Mason (Sussex), 24 Jan 05 03:35

I could have sworn the voltage drop coincided with the light going out.

- (#15003) Ian Dunse (Derbs), 24 Jan 05 04:10

Nope, the post-heat is for emissions control, Dave.

The light is an arbitary "it's OK to start" indicator, it's normal (in most makes) for the plugs to do something completely different altogether.

Like in the Pug HDI, the light won't come on at all unless ambient temp is below 18c yet at that temp there could be 30secs of postheat. Bizarre eh?

- (#15003) David Miller, 24 Jan 05 04:36

Sorry, I wasn't disputing the reason for the post-heat overun - to make the engine run better. I was pondering why the first few seconds are at a higher voltage, having observed that the voltage will reduce before the engine starts if you slow to operate the starter.

Sorry Gar, this discussion is not helping you with the original problem. Let us know if the light "on" meant a faulty glow plug in your new shape Ace.

- (#15003) Dave Mason (Sussex), 24 Jan 05 04:59