Rear Dif lock fault

[RainowMan]

Hi there,

I have a problem with my read diff activation.

I recently purchased a replacement genuine "T"rear diff lock actuator from Milner off road. Last time I used them was abou 8 years ago and they didn't carry much for the 100 series.

I fitted the actuator as per manual instructions and it still doesn't work. I've been looking at the FSM and a manual I purchased from Milner.

With the engine running and driving back and forward the RR diff red symbol illuminated on start up and stayed on. It felt like the truck didn't want to turn so I think the diff was definitly engaged ( I had. To engage the diff to fit the actuator as per manual installation process)

I've checked the actuator ball bearing switch continuity O.K and this goes from flashing to SOLID and back to off When removed and manually depressed by a friend whilst I turn the switch on/off.

I have checked the RR Dif dash switch continuity this appears fine.

Before I replaced the rear Diff actuator when the switch was turned the abs symbol would illuminate and the red Rear Dif light would flash but not go solid. The diff was seriously rotten so I know it couldn't have worked.

The middle diff seems to switch on/off fine. when the engine is switched off you can hear a 1 or 2second fast wirr noise as it engages/disengages.

The diff/abs lights also appears to work in Low box as described in the FSM and other manual.



I have tried to follow the FSM diagnosis section.

The selector fork inside the diff appears to manually disengage easily when back axel if jacked up.

RR dish dash Switch o.k

Couldn't locate the "Rear diff ECU" the FSM diagram is seriously basic. I did however find a "computer 4WD system" block with a 10 pin connector located under the dash on the offside wall. Can anyone guide me to the Rear Diff ECU? Do I check the input or output of the ECU?

The FSM also covers using the main heater relay, car battery and lots of bespoke wires with connectors between the three components to test the actuator. Is this test done directly onto the rear actuator side of the multi pin connector (five wires). Can I do this test with the actuator removed? As I've put the old one back on for now to allow me to drive safely as I felt the diff fork moved to freely and could engage around a extreme corner and send me off the road! The old one is well seized so I can't see it allowing the fork to enguage! Fingers crossed!!!

It also mentions jacking up the entire vichicle during the above ECU diagnosis. Is this critical to the diagnostics?

Do / should I check continuity between ECU output and the multi point connector just before the actuator. The FSM doesn't seem to have a wireing diagram for the diff system and the Milner manual seems to have completely different coloured wires my actuator has: thick Green, thick Green red stripe, yellow, green and black all going to a 6pin connector with pin 1 missing. Both new and old connectors look identical.

Does the ECU controll all diffs? As I'm nearly certain my mid-diff works as it should.

Does anyone have a used but Fully funtional Rear Diff ECU I could buy/try?

Regards,

ed.

 

[Chris]

It's usually far more fundamental than this. Let's hope. I would have connected the locker to the harness before mounting it and using the switch, cycle it a couple of times. What I have found (at least twice) is that the locker is in the wrong part of the cycle when mounted. ie it's out of sync with the switch. Yes, there are loads of other bits of wizardry in there as you mention, but to me this sounds pretty classic - out of sync.

You may have done this already. if you have then clearly everything is working correctly - which would mean that you wouldn't have this problem.

Chris

 

[Jon Wildsmith]

I'm confused, you say it doesn't work but then you say the light went solid and it felt like it had engaged when you drove the car?

 

[RainowMan]

Hi sorry,

Historically the red light would flash without going to a solid light. I knew there was an an issue as the original actuator cog casing was rotten but still sealing the differ I lived without it!!!

Both FSM and other manual say to set the diff to locked to fit/remove the actuator. If you try to fit the actuator in the unlocked position the actuator stops 8mm or so from contacting its mounting surface. Not sure why?!?

So I manually set the diff fork to locked to fit the new unit and bolted it up. When I switched the engine on I got the solid red RR diff light. I tried driving back and forth, shifting up and down but the light stayed on.

I Then removed the actuator and the switch to release the push rod but left it plugged in and manually pressed the actuator switch (like ball bearing) to see if the actuator would cycle in or out to no avail.

When You press the central Diff lock button you can hear it cycle and you can also hear a relay click. When I turn the rear RR diff lock not a whisper...

Maybe I can do a volt check at the actuator end of the 5 pin plug? Maybe the new actuator is a dud but I paid less than 1/2 Toyota dealer price and they don't have any more stock!!!

Regards,

Ed

 

[Jon Wildsmith]

ok, I'm with you now. The ball switch is just for the dash light, the ECU takes no notice of it for powering the actuator. What year is your truck?

Have you manually moved the rod that sticks out of the new actuator?

 

[RainowMan]

Hi it's a 1998 4.2TD 24v auto.

I did try but not very hard there was a little movement but nothing more than 1to2 mm. Should I be able to pul/push the rod on the actuator?

Thanks,

Ed

 

[Jon Wildsmith]

Should I be able to pul/push the rod on the actuator?

Not easily. Usually you can't fit a rear diff actuator unless either it works so twiddling the knob pulls the rod in/out or you force it. Otherwise, if the rod is in the lock (extended) position you can't quite get the actuator seated or if the rod is in the unlocked (retracted) position the hole in the fork won't line up with the hole in the rod. Did you have any problems like that? I'm wondering if your rod is in a mid way position.

On the actuator, check for continuity between pin 4 (W-B) and either pin 5 (G-Y) or pin 6 (G-R). Those are the pins that tell the ECU what position the actuator is in with pin 4 being the common. No continuity on one of those = no motor power from the ECU. If neither has continuity then try moving the rod, either manually or by briefly applying power to pins 2 (L-R) and 3 (L). The motor should run and the rod should move if it isn't already at the full extent of motion for that orientation of power. Swapping the power round will run the motor the other way. There is no cut out powering the motor this way so don't let the motor run too long after movement stops.

That should let you establish if the actuator is ok or not so let us know what you find and we can carry on with the diagnosis

 

[RainowMan]

Hi,

At first the diff actuator would not seat by 6-8mm so we jacked the rear and slowly turned the wheel to engage the diff allowing the fork to move towards the centre of the vehicle (inwards) the required 6-8mm.
Since the old actuator split into components it exposed a large plastic cog with a contact side in metal with three brass contacts. There was a blank for the outer and inner contact I imagine the stop and start you mention.

Can the cog casing be opened to visually see where the contacts are sitting?

Since the upper and lower contacts have blank spots at different segments of the face I can't see how it can get stuck in one position?

I'll check the continuity this evening. When you say power up the actuator should I come straight off a 12v battery or use the heater relay as described in FSM? If i use the heater relay I am worried about blowing the heater relay as I sure it expensive!

Regards,

Ed

 

[Jon Wildsmith]

I'll check the continuity this evening. When you say power up the actuator should I come straight off a 12v battery

Yes, just mind what you touch the wires onto and how long for. I would avoid taking the actuator apart if you might need to return it to Milner. There are other places to get actuators and possibly slightly cheaper than Milner if you're not in a rush but you need to work out if it's the actuator or car and the actuator is the easiest to test.

 

[RainowMan]

I've just been down to RRG in Macclesfield and they couldn't find the Rear Diff lock ECU on their system? The only thing they could locate in the Computer 4WD Unit I mentioned yesterday.
Hmm...

Still don't understand why both manuals refer to this illusive 'Rear Diff lock ECU'

ed

 

[Jon Wildsmith]

It should be above the drivers side kick panel, is fairly small and may be the part the EPC labels as the 4WD Controller, or not Do a search as I'm sure its location has been mentioned somewhere on here.

 

[RainowMan]

Sorry treble a pain Jon,
Should go straight onto a 12v car battery? I've made up some cables which fit onto the actuator plug pins to avoid touching anything else.

I think I'll leave the on vehicle tests until tomorrow as is well and truly wet here! When testing the vehicle electrics do I do this at the actuator end which is still plugged into the computer/ECU?

Thanks,
Ed

 

[Jon Wildsmith]

I would go straight to a 12v car battery yes and the tests I mentioned were for the actuator with it on the bench.

 

[RainowMan]

Hi,
Just checked the actuator on the bench giving the following results:

1. Continuity on pins 4 & 6.

2. 12v Live up motor rod extends. (1sec)

3. Continuity on pins 4 & 5.

4. 12v Live up motor (reverse connections) rod retracts. (1sec)

5. Continuity on 4 & 6.

Looks like the actuator is fully functional.

So it's looking like the 4WD computer black box (10 pin connector) given the above results? Any idea where I can get a used tested one from? In the mean time I will ask Simon mr T to price one up...?

Since the old actuator shaft is seized perhaps it cross wired or damaged a circuit in the 4WD computer box?

Wow, thanks for you're concise help! Forums are truly amazing!!!

Regards,

 

[Jon Wildsmith]

Progress of a sort The problem need not be the black box, it could be in the wiring, for example it's not unknown for the conductor of a wire to be corroded or just broken where they exit the connector on the car side of the actuator connector but the insulation outer makes them look ok. Could also be a problem with a signal the black box needs to see before it will do anything e.g. doesn't think CDL is locked, or not in low box or something like that. If it is the black box, unless a replacement is quite cheap I would open it up to try and repair it as it could just be a dry joint or something simple to repair.

I would check a few things now on the car side of the actuator connector with the actuator disconnected. Pin 4 (W-B) should show continuity to -ve / earth regardless of switch position etc so check for continuity between pin 4 and earth as without that nothing will work. For pins 5 (G-Y) and 6 (G-R) you'll need the centre diff to be locked, I think you'll need to be in low box as well in a 100 but it won't hurt if I'm wrong, with the ignition on so the dash is all lit up. With the rear diff lock switch in the off position, pin 6 should show +ve (whatever your battery voltage is). Turn the rear diff lock switch to the on position and pin 5 should show +VE instead. It's possible I have those the wrong way round but they should swap round when you go from off to on and back again.

I'm assuming at this point you can get the centre diff to lock because you mentioned that and it isn't just a blown diff fuse

See how you get on with those tests before we get to pins 2 & 3 because they will be a little trickier to test.

 

[RainowMan]

Hi,
Sorry I've not had a chance to do the tests tonight. I've been trying to sort my golf GtTDI. Nightmare.

I took it to he garage and asked them to check the VNT lever and. Actuator as I couldn't get into it to remove the circlip. So they told me the turbo was complete.y knocked and vanes were seized.
So I asked them to remove it and I would clean it. So they removed It and didn't even check the VNT lever. So after all that it was the actuator.

I found a new actuator and gave it to them to fit. All good? naaaaaa

10 mile s later no turbo!!

After some digging around I found that the self locking nut on the actuator arm hadn't been locktite as clearly stipulated. So it had vibrated down and James the actuator from retracting. Now its back to square 1 no boost!!!

What's wrong with people!?