mikevernon@talktalk.net

In all the time I've had my C4 I've never used the **** on the centre console, but now that I'm selling it a possible buyer is querying whether or not the differential lock is working. How can I tell?
If I turn the **** clockwise I hear a single clonk.
If I turn it anticlockwise I hear 4 or 5 clonks in rapid succession.
The handbook tells me that there should be a flashing yellow light on the switch when it is on, but I can't see any sign of it.
When I start the car the red warning light on the dash comes on with the other system check lights, then goes off again when the others go off.
Does the lack of red light on the dash mean that everything is ok, or does the lack of fllashing yellow light on the switch mean that there's a problem?

garrett376

It sounds like the bulb is burned out to illuminate the yellow light. If you hear it working (clonks as you say) and never get a warning light when driving around, don't worry about it!

mikevernon@talktalk.net

Crikey, that was quick!
That sounds like good news. I hope I can convince the buyer!
I'm still not 100% convinced though. Does the clockwise single clonk turn it on, or is it the anticlockwise multiple clonk? And if I drive at low speed with it on, will the red warning light on the dash light up to remind me or does the (non-working) flashing yellow light serve that function?

DaveK

I wonder why your buyer cares anyway. I've had my car 5.5 years and never used it!

Southampton76

Pull the oil gauge, find the blub blank with the green AWD symbol and pop in a spare bulb. Then go take it for a ride over a bumpy road. Watch the green light shine!!! :-) It shows its working if he needs proof

garrett376

Unless your C4 is a 93 or a 94, then the green light does not work - wiring was deleted from these cars to the gauge.

Dave... new girl?

DaveK

That's my future wife - although she doesn't know it yet - Amy Lee from Evanescence. I did hear she got married in January, which I think is quite unreasonable, but I'll forgive her once they get divorced.

colo964

The clonks you hear show the brain and hydraulics are fine. You can pull the ABS relay or fuse which de-energizes the diff locks. There will be no clonks. If he wants more proof, switch it on then have him try to do a U-turn on dry pavement. The front end will groan and skip. Then charge him extra for wearing out the diff, tires and possibly your hydraulic actuators.

Another test is to drive it on ice, if there is any around. Mud is nice too. I've gotten in and out of both using the lock (yeah, I know it's pet abuse but a nerd's gotta have some fun).

SimonExtreme

I showed her this in bed this morning and she said "keep dreaming"

Red rooster

Turn the switch to the right to lock the diff. Then try a tight turn in a car park . It will drive like a tank if you keep the speed down !
That will encourage you to turn it off

Geoff

frankvan

If you install a bulb in the green PDAS indicator it should flash when the diff lock is engaged. When you disengage it manually (ie at rest) there will be one long flash of the green pdas light then its done. Mine does this at least.
Also, if you have the scantool interface you can check out the PDAS unit. Again, with mine the ignition has to be in the "RUN" position but with the engine NOT running (not sure if this is the same for other model years)/ When it hooks up to the PDAS I hear a clunk (diff lock engaging) and again the green pdas light flashes until the scantool disconnects from the PDAS.

One final alternative is to find some ice and try starting off on it with and without the diff locked and see if there is any difference. The only difference I found is that it pulls perfectly straight with the diff locked whereas with just PDAS it will sometimes start a little squirelly and then straighten out.

Red rooster

Sorry to repeat but the diff lock system working is extremely obvious !

Turn the diff lock on and try doing a parking manouvre at low speed . The steering should feel absolutely awful ! Solid and very heavy . If you dont get that contrast in steering feel the sytem isnt working. Takes moments to see if there is a problem !

Geoff

--------------------------------------------------------------------------------
KS400200 , the oldest 964 on Rennlist , unless you know differently !

mikevernon@talktalk.net

Geoff, you were absolutely right. I turned on the diff lock and drove around the car park, and it felt every bit as bad as you said it would.
So it is working! Marvellous!

The Porsche specialist who came to inspect the car last week on behalf of the potential buyer reported that the diff lock wassn't working, presumably because he couldn't see a flashing yellow light!

Thanks for your advice.

Mike

garrett376

That's quite the diagnosis for a Porsche Specialist. Yikes!

tbennett017

my light flashes when rolling slowly over speed bumps.. its pretty sensitive to differences in wheel speed.