Hello, 

 

My Skoda is having trouble starting during cold weather. All four glow plugs, glow plug control module (GPCM) have been replaced. I have checked fuses, power supply, wiring from PCM to GPCM to glow plugs. Everything is ok, no corosion or water or anything. Pin 9 on GPCM connector is showing ~9.4V I assume its a lin bus. Pin 10 shows ~3.4V (with different GPCM it shows ~5.2V, not sure what the actual value should be) thats a signal wire I assume and I can confirm it reaches PCM. Still im getting P0684 glow plug control module - implausible signal fault. When running a test, current is not supplied to any glow plugs, and funny thing is that it doesnt matter, if the GPCM is connected or not, VCDS is still giving me this fault. Im lost :( any ideas? Thanks!

If anyone encounters same symptomps here is the UPDATE: 

 

It was ECU fault. After replacement and coding everything was fine

It looks like you have been more advanced than I have on this fault ....

 

The other week I got the enginer management light come on.  bought a cable and software and the fault was .. exactly..

 

Stored DTC(S)

P0684 - Glow Plug Control Module to PCM Commmunication Circuit Range Performance

 

I found a great webiste here ... https://www.obd-codes.com/p0684 which pretty much covered everything ... apart from where all the respective componants live??

 

Anyway ... I reset the code but seeing as the ambient temperature is great today I'm not really surprised the fault hasn't returned.   It's got a its service due in a few months and so I'd really like to sort this myself before then.

 

You obviously have some idea where these items 'live' so please give me a clue?  Thanks

 

Also, you say and ECU fault ... are they not an expensive item to have to replace?  If it is an ECU fault ... would it not appear even in warm weather?

 

THanks