Diff lock not working

Skewif · Sep 24, 2023

Not used the diff lock in a while and only found out it’s not working when I really needed it. Button on dash lights up when pressed but nothing happens and no warning in MFD. Has anyone else had this problem? Currently off road in mountains and really hoping to find a fix as have just discovered how easy it is to get stuck without it.

larrylamb · Sep 24, 2023

Hi, sounds like a solenoid issue. Quick google seemed to confirm, and found this fix for similar T5.1 on T4 forum.

"So since buying my 4motion I have had no difflock. Pushing the dash button got a click from the relay under the steering column but no light on the dash and certainly no locked rear axle. Finally got around to investigating the issue. Removed undertray from below passenger seat to reveal the vacuum solenoids that control the difflock mechanism and did some testing. First removed pipe from engine and with engine running checked there was a vacuum. All good there. Then checked the release solenoid (green pipe) by pulling it off the solenoid. Sucking well from the port. Remove the wiring connection and suck stops. So all good. It is worth remembering that this solenoid is energised every time the vehicle starts so is never idle. Then pressed difflock switch and pulled blue pipe on the otherside that should send the vacuum to the difflock engaging solenoid on the rear axle and nothing. Pulled the connection. No click or movement from the solenoid. OK so swap blue and green pipes over and change over the connections (effectively swapped out the sloenoids) and CLICK - SUCK. Crawl out and there is the difflock light on the dash. Bench tested the "faulty solenoid and it is dead as a dead thing. Luckily they only seem to be about £15 to replace.

So a word of advice. Whereas the "disengage" solenoid (green pipe) energises every time the engine starts, the engagement solenoid (blue pipe) only ever energises when the difflock is used. I am guessing mine was never used over the past 6 years and has ceased solid. So definitely worth pressing the difflock button if you have it every now and again, just to keep it free. You don't have to be driving to operate it.

Hope this helps. It is pretty easy to change and I can see no reason why the new one won't fix it when it arrives."

https://www.vwt4forum.co.uk/threads/t5-1-difflock-not-working-solved.1306122/