Fiesta - where is the glow plug relay?

mrc61 · 27-10-2020, 09:16 PM

Hi all,

Just replaced all four glow plugs but cold starts did not improve.

Battery is good, 60 A glow plug fuse is good, so I figured it's probably the glow plug relay (assuming that there must be one somewhere).

I monitored battery current as I turned ignition on and expected at least 40 Amps because each glow plug should draw about 10 Amps. I didn't see even 10 Amps hence I assume none of the plugs is getting any juice.

Does anyone know where the glow plug relay would be on a 2010 LX Fiesta?

raceteam · 28-10-2020, 04:44 AM

I don't know where the relay is, but there is an additional fuse box behind the glove if you didn't already know.

mrc61 · 28-10-2020, 02:49 PM

Quote:

Originally Posted by raceteam

I don't know where the relay is, but there is an additional fuse box behind the glove if you didn't already know.

Thanks raceteam, but that one is for smaller electronic stuff. The heavy-duty circuits are mostly in the fusebox next to the battery and I expected the relay (or controller) to be somewhere nearby there too, but I can't spot it. I would follow the wiring to the glow plugs if I could see them, but they're buried in a tight space between the engine and the firewall.

simon varley · 28-10-2020, 09:49 AM

glow plugs should only be active under a certain outside temperature. I don't believe they come on over about 4C. May be wrong though.

mrc61 · 28-10-2020, 02:51 PM

Quote:

Originally Posted by simon varley

glow plugs should only be active under a certain outside temperature. I don't believe they come on over about 4C. May be wrong though.

They do seem to be temperature dependent, so at least I don't think that the dash indicator comes on when the engine is warm.

11ford11 · 29-10-2020, 01:42 PM

Near battery-fuse box 1 has fuses and relays left side 2nd down from top iirc

mrc61 · 29-10-2020, 10:33 PM

Quote:

Originally Posted by 11ford11

Near battery-fuse box 1 has fuses and relays left side 2nd down from top iirc

Thanks 11ford11 - I had initially dismissed that relay because the manual called its function 'ignition' - which in retrospect, probably is for the glow plugs, but I thought it had another function. It's rated at 70 Amps which sounds about right for 4 x 10 Amp glow plugs.

Unfortunately the relay appears to be working in that the 70 Amp contacts make when 12 V is applied to the coil.

I also checked that there was voltage going to the coil when the ignition was turned on. The voltage appeared to stay there as long as the ignition was on - that is, it did not time out after 5 or even 10 seconds. (The relay was not plugged in for this test.)

So the question now is why don't the new glow plugs pull 10 Amps each? I still don't reckon that they are seeing any volts.

Not sure what my next step should be.....

Any tips welcome!

11ford11 · 29-10-2020, 10:58 PM

Are you sure it doesn’t switch the earth side of the relay to pull it in

Check with a test light or multi meter for power at relay contacts and see if you loose it when you remove glow plug fuse

Bridge relay socket contact connections while checking for power at glow plug connections.
Don’t leave on long time just long enough to test

mrc61 · 30-10-2020, 05:28 PM

Quote:

Originally Posted by 11ford11

Are you sure it doesn’t switch the earth side of the relay to pull it in

Check with a test light or multi meter for power at relay contacts and see if you loose it when you remove glow plug fuse

Bridge relay socket contact connections while checking for power at glow plug connections.
Don’t leave on long time just long enough to test

Hello again 11ford11,
Thanks for your suggestions....
Pulling the 60A glow plug fuse does not remove +12V from the Ignition Relay (2nd one down on the LHS), however pulling the 60A Ignition Relay fuse does indeed remove the +12V from the Ignition Relay socket contact.

That leaves me wondering what the function of the Ignition Relay is, and also whether there is still a separate Glow Plug relay that is yet to be discovered.

With the Ignition Relay withdrawn, I bridged the two socket contacts (the fat ones) and measured both the bridging current and the battery current:

Bridging current = 0.3 Amps
Battery current = 3.0 Amps

When bridged, another relay can easily be heard operating on the other side of the engine (I can't actually identify where it is). It is quite a loud 'clunk'. And this is presumably what is pulling most of the 3 Amps.

Interestingly, when the car's ignition is switched on to the position where the glow plugs should be powered, this same loud relay does not operate. However, at the same time, the Ignition Relay gets 12 Volts to its coil circuit. That is confusing!

Unfortunately I can't even see (with a mirror and torch) the wiring to the glow plugs - let alone find, or put a meter on the wiring.

Also of interest, is that the resistance to earth of the non-hot socket contact for the Ignition Relay is 10k Ohms - not what I would have expected if that contact was connected to the four glow plugs in parallel.

I am fresh out of ideas now......

11ford11 · 31-10-2020, 08:08 AM

Suggest try testing power at relay 3 while removing glow plug fuse apply the same for other large relays
also have you scanned for codes - copy and clear if present as the system may have locked out if it sensed faulty glow plugs

mrc61 · 01-11-2020, 09:12 AM

Quote:

Originally Posted by 11ford11

Suggest try testing power at relay 3 while removing glow plug fuse apply the same for other large relays
also have you scanned for codes - copy and clear if present as the system may have locked out if it sensed faulty glow plugs

Thanks again 11ford11 - Removing the glow plug fuse did not affect the +12 V at Relay 3 (PCM relay) or Relay 1 (Cooling System Fan Relay), and there aren't any other relays with sufficient rating for the glow plug circuit in that fuse box.

I scanned for fault codes but didn't get any. I noticed that my scanning application reported that it wasn't connected to the ECU, however the scan appeared to proceed normally. I have a friend coming over later today to try his scanner.

11ford11 · 01-11-2020, 10:44 AM

Is relay 2 a 5 terminal relay and others 4 terminals
What number is glow plug fuse
Is vehicle ws or wt
Verify engine type

mrc61 · 01-11-2020, 10:55 AM

Quote:

Originally Posted by 11ford11

Is relay 2 a 5 terminal relay and others 4 terminals
What number is glow plug fuse
Is vehicle ws or wt
Verify engine type

Relay 2 is 4 terminal, as are Relays 1 & 3. Coil is ~72 ohms, and main contacts are Normally Open.

Glow Plug fuse (60 Amps) is Fuse 8.

Vehicle is WT

Engine is 1.6 litre turbo diesel.

mrc61 · 06-11-2020, 09:07 PM

FYI, the glow plug relay has been found: It's located under the LHS headlight assembly. Talk about hidden out of sight!

11ford11 · 07-11-2020, 08:22 AM

Quote:

Originally Posted by mrc61

FYI, the glow plug relay has been found: It's located under the LHS headlight assembly. Talk about hidden out of sight!

Good to hear-For my notes Relay or module? Was it working?

mrc61 · 07-11-2020, 08:47 AM

Quote:

Originally Posted by 11ford11

Good to hear-For my notes Relay or module? Was it working?

It was an auto-electrician who found it and I haven't seen it yet but understand that it's a simple relay, connected such that the PCM provides the ground signal to operate it.

The relay was found to be in working order, but the problem is that the PCM isn't providing the ground signal. The wire from the PCM to the relay is intact.

On the surface, it would appear that the PCM may be faulty, but that assumes that the appropriate input signals are being received by the PCM. At a cost of nearly $2200, and considering the age of the car, replacing the PCM is out of the question; it would be far cheaper to install a 'cold start' push button switch to manually operate the glow plug relay.