Does anyone know if this is a relay or is it a module that controls how long the glow plugs are on for? If its a relay, what are the pin connections for the relay coil?

I have the engine management light on and VCDS reports a Implausible Signal from the module, any ideas?

I have the same thing, starting cold, but in these rare times I switch the light off with obd11. Most of times using Webasto in the mornings and no warnng appears.

But would be interesting to know too.

Well, I've just bit the bullet and ordered anew one on eBay and it will be here tomorrow, so will soon now if it cures it or not.

I vaguely recall them being solid state, from taking one apart several years ago.

2 hours ago, Breezy_Pete said:

I vaguely recall them being solid state, from taking one apart several years ago.

I think so as well, as there is no possible way that they could produce an error code otherwise. It is possible that it has faulty for sometime but has only announced it self owing to lower temps in the mornings now. It has not struggled to start yet, new one will be plugged in as soon as it arrives and the DTC cleared.

16 hours ago, Graham Butcher said:

Well, I've just bit the bullet and ordered anew one on eBay and it will be here tomorrow, so will soon now if it cures it or not.

What did you order exactly?

P.S. surpisingly VCDS could not take the warning light out, but obd11 did.

Edited 15 October, 202515 Oct by linni

7 minutes ago, linni said:

What did you order exactly?

P.S. surpisingly VCDS could not take the warning light out, but obd11 did.

I ordered the replacement plug in module, which looks like a relay and it lives in the engine bay fuse box. It's the big square one in the back left corner of the box, looking from the front of the car.

Cost was £51, with free next day delivery by DHL, from a seller on eBay. Once I get to my computer, I can post a link to it if you want?

Currently the engine starts on the button, but as the temperature is dropping and will soon be into minus numbers first thing in the mornings, the glow plugs will be really helpful in starting.

1 hour ago, linni said:

What did you order exactly?

P.S. surpisingly VCDS could not take the warning light out, but obd11 did.

Here is the link as promised.

Glow Plug Control Unit 0281003085 Bosch ECU 038907281B 132129 2502129 GZS New | eBay UK

DHL should be delivering my module this evening between 18:46 and 19:46, so I hope to cure the problem by plugging it and clearing the fault code, fingers crossed.

DHL have just delivered the module, fitted it and for the first time since I have owned this Kodiaq, I have now seen the glow plug warning light come on, indicating that the glow plugs are operating correctly, job sorted. Error codes have been deleted, taken her out on a quick trip for around 10 miles, no problems switched off, waited for a few minutes and switched on again, no errors, brilliant.

On 14/10/2025 at 14:15, Breezy_Pete said:

I vaguely recall them being solid state, from taking one apart several years ago.

You are correct, they are solid state. I expected that the cap shown was likely to be the culprit, but no, it was well within is tolerance figures both for the ESR and cap value which came in a 460vF, just 10 away from its design value, so well within it operating values.

20 hours ago, Graham Butcher said:

DHL have just delivered the module, fitted it and for the first time since I have owned this Kodiaq, I have now seen the glow plug warning light come on, indicating that the glow plugs are operating correctly, job sorted. Error codes have been deleted, taken her out on a quick trip for around 10 miles, no problems switched off, waited for a few minutes and switched on again, no errors, brilliant.

Good, as I read meanwhile that the same error could be caused by glowplug nr. 3, which has some sensors and costs around 200 euros.

8 hours ago, linni said:

Good, as I read meanwhile that the same error could be caused by glowplug nr. 3, which has some sensors and costs around 200 euros.

I know about that special glow plug pressure sensor on nr.3 cylinder, I had that on my Superb, however, when I plugged the VCDS in I got a different error message. If I remember, it said something about the signal coming from that sensor not being plausible, but I remember I was getting the glow plug symbol lighting up briefly after switching the car on. On the Kodiaq, I never had that symbol until I replaced the module, are you seeing the symbol lighting up in the top of the instrument cluster?

Have you got the virtual cockpit or the analogue instruments, if virtual then the lamp will be in the light cluster at the very top of the display, otherwise I think it appears beneath the dot matrix between the dials.

So I would guess, that if you are getting a message about the module, then it will be the module, if it mentions the sensor, then it will the sensor (ouch) or the connection to it might be suspect.

Yes, the glow plug light comes on every time they do their job. Sometimes, when it is cold, for several seconds.

But as I already told, I usually use Webasto and glow plugs just rest.

I have virtual cockpit.

Not that I desperately need one, but glow plugs are also used during the regeneration and it's better to change the module. Costs about 60 euros here.

Well in that case, I have doubts that changing the module will solve your problem. What I'll do later is to sent you the actual VCDS report I have saved for my problem so you can compare it against yours to double check that yours is reading the same as mine or if the wording and fault code is different. No point in wasting an extra 50 euros for nothing.

4 hours ago, Graham Butcher said:

Well in that case, I have doubts that changing the module will solve your problem. What I'll do later is to sent you the actual VCDS report I have saved for my problem so you can compare it against yours to double check that yours is reading the same as mine or if the wording and fault code is different. No point in wasting an extra 50 euros for nothing.

Would be very helpful, thanks!

10 hours ago, linni said:

Would be very helpful, thanks!

Here is the section of the VCDS log for the fault.

Address 01: Engine (J623-DFGA) Labels:. 04L-907-309-V1.clb

Part No SW: 04L 906 026 QT HW: 04L 907 309 P

Component: R4 2.0l TDI H25 6582

Revision: B4H25--- CVN: 7C29C05F37C5C2A218229D33

Coding: 0125001203661D083000

Shop #: WSC 33361 790 00137

ASAM Dataset: EV_ECM20TDI01104L906026QT 004006

ROD: EV_ECM20TDI01104L906026QT.rod

VCID: 0C42AEC176C802FAE2B-8058

VINID: 91D49D6877A301B200142208040223A0A6

1 Fault Found:

4976 - Glow Plug Control Module (J179)

P0684 00 [00100111] - Implausible Signal

Not Confirmed - Tested Since Memory Clear

Freeze Frame:

Fault Priority: 2

Fault Frequency: 1

Mileage: 159125 km

Date: 2025.10.11

Time: 12:52:32

Engine speed: 0.00 /min

Normed load value: 0.0 %

Vehicle speed: 0 km/h

Coolant temperature: 56 C

Intake air temperature: 59 C

Ambient air pressure: 1020 mbar

Voltage terminal 30: 12.180 V

Unlearning counter according OBD: 40

Electric auxiliary heater: shut-off conditions-Bits 0-7: 0

Electric auxiliary heater: shut-off conditions-Bits 0-7: 0

Electric auxiliary heater: relay activation-Bits 0-7: 0

Pre-glow time: 0 ms

Glow status-Bits 0-7: 0

Glow status-Bits 0-7: 0

Glow cycles above temperature threshold-Bits 0-7: 0

Glow cycles above temperature threshold-Bits 0-7: 8

Glow cycles below temperature threshold-Bits 0-7: 2

Glow cycles below temperature threshold-Bits 0-7: 71

Outside temperature sensor 1: B1: raw value: 20.0 C

Readiness: 0 0 0 0 0

Mine is slightly different. Different part number and fault code:

Address 01: Engine (J623-CUAA) Labels:. 03N-906-026-CUA.clb

Part No SW: 03N 906 026 J HW: 03N 907 309

Component: R4 2.0l BTD H24 6584

Revision: A1H24--- CVN: 4E80DD7F37C5C2A218229D33D6C3ECFE

Coding: 01250012047605083000

Shop #: WSC 32912 056 526860

ASAM Dataset: EV_ECM20BTD01103N906026J 004004

ROD: EV_ECM20BTD01103N906026J.rod

VCID: 323D185DA4A2CD1A487-8066

VINID: 91D49C7477A31DB20014420408A20FBA15

4997 - Glow Plug Control Module

P064C 00 [01100101] - -

Not Confirmed - Tested Since Memory Clear

Freeze Frame:

Fault Priority: 2

Fault Frequency: 1

Mileage: 485811 km

Date: 2025.08.17

Time: 09:36:57

Engine speed: 0.00 /min

Normed load value: 0.0 %

Vehicle speed: 0 km/h

Coolant temperature: 15 C

Intake air temperature: 15 C

Ambient air pressure: 990 mbar

Voltage terminal 30: 12.240 V

Unlearning counter according OBD: 40

Electric auxiliary heater: shut-off conditions-Bits 0-7: 0

Electric auxiliary heater: shut-off conditions-Bits 0-7: 0

Pre-glow time: 1500 ms

Glow status-Bits 0-7: 0

Glow status-Bits 0-7: 0

Glow cycles above temperature threshold-Bits 0-7: 0

Glow cycles above temperature threshold-Bits 0-7: 3

Glow cycles below temperature threshold-Bits 0-7: 0

Glow cycles below temperature threshold-Bits 0-7: 1

Outside temperature sensor 1: B1: raw value: 13.0 C

I think that this is essentially the same issue that I had. It clearly states the Glow Plug Control Module and a few minutes googling also says it is the same. The different part number and the code is just a by-product of the manufacturer maybe, being a different maker.

My old one was made by HKR Seffer Automotive, but the replacement is made by Bosch, has a different part number etc, but the important bits are the same, the pins and the method of control remain the same, as does the physical size etc and the seller says that the part is fully compatible with my car as it is listed as a direct replacement part.

So, on that basis I personally would go right ahead and replace it with another one that is either same or its equivalent, it has cured my issue, and the error has now completely vanished.

Thanks, Graham.

Just my thoughts. Will order the module. Takes couple of weeks to get under the bonnet, but will report back.

51 minutes ago, linni said:

Thanks, Graham.

Just my thoughts. Will order the module. Takes couple of weeks to get under the bonnet, but will report back.

OK, please keep me updated, but why does it take a couple of weeks?

This video shows how easy it is, you don't need to remove the engine cover either, but it is only a push on cover so will just lift off if you pull it upwards.

Edited 18 October, 202518 Oct by Graham Butcher

Just other stuff constantly to take care of, that's why couple of weeks (probably) :)

I see, but in all honesty, it just takes about 10 minutes max to swap the module over and clear the fault code.

Ordered the module yesterday, will arrive in couple of days. I know th swap is piece of cake, will do as soon as it arrives.

Bought this one for 61 euros:

https://spareto.com/products/metzger-relay-glow-plug-system/0884010

It had number 457 on the back instead of 527 as original, but works just fine, no more faults anymore.