Hilux 4x4 Forum

Hi i have 2001 lux 4x2 and i have a problem with my diff lock light not switching off. Please can someone assist me .

Hi Greg and welcome to the forum!

Is it just the light that stays on, or does the locker remain engaged as well?

The Gearmax locker is vacuum operated and controlled by a vacuum solenoid valve. When you engage it normally, first the red light comes on to indicate that the solenoid is open (vacuum going through to the locker), but the green light only comes on once the locker has meshed in the diff. That sender unit for the light is in the rear diff.

If it's just the light, disconnect the wire from the hexagonal plate at the diff and see if the light goes off. If it does then there is a problem with the switch inside. If not,that wire is grounding somewhere .... could be hurt or chaffed through. You would have to follow it and check where.

If the locker remains engaged, it could be either of two possibilities. The solenoid valve is leaking and vacuum is still going through to the diff, Just disconnect the vacuum pipe at the diff to see if it disengages. If this is the fault, the vacuum solenoid would need to be replaced.
More commonly it's just a case of a blocked diff breather. If the breather blocks pressure builds up in the diff as the air in there warms up ..... this pressure presses against the diaphragm from inside the diff resulting in the same as if there were vacuum on the other side of it, and the locker engages.
Remove the breather, clean it with some petrol or paraffin and replace.


Let us know what you find.

Mud Dog wrote:Hi Greg and welcome to the forum!

Is it just the light that stays on, or does the locker remain engaged as well?

The Gearmax locker is vacuum operated and controlled by a vacuum solenoid valve. When you engage it normally, first the red light comes on to indicate that the solenoid is open (vacuum going through to the locker), but the green light only comes on once the locker has meshed in the diff. That sender unit for the light is in the rear diff.

If it's just the light, disconnect the wire from the hexagonal plate at the diff and see if the light goes off. If it does then there is a problem with the switch inside. If not,that wire is grounding somewhere .... could be hurt or chaffed through. You would have to follow it and check where.

If the locker remains engaged, it could be either of two possibilities. The solenoid valve is leaking and vacuum is still going through to the diff, Just disconnect the vacuum pipe at the diff to see if it disengages. If this is the fault, the vacuum solenoid would need to be replaced.
More commonly it's just a case of a blocked diff breather. If the breather blocks pressure builds up in the diff as the air in there warms up ..... this pressure presses against the diaphragm from inside the diff resulting in the same as if there were vacuum on the other side of it, and the locker engages.
Remove the breather, clean it with some petrol or paraffin and replace.


Let us know what you find.

Andy, i second you on the diff breather, that would be my first port of call. I had it happen to me many times.

Quite true Craig, those breathers can stick and block fairly easily .... don't know why Toyota never foresaw this and employed a better design. However, Greg doesn't mention that the locker itself remains engaged, so I went the lengthy route and explained the alternate scenario. Just hope that it helps him.

An afterthought, Greg .... I didn't mention because I assumed it would be common sense, but if the locker remains engaged, do NOT drive the vehicle, especially not on a hard surface. You WILL damage the diff!

Thank you very much for the info. The green light stayed on , so i gathered that the locker was engaged . I pulled the vacuum pipe off and drove the bakkie , when i stopped and checked the light , it was red and i was able to turn off light. Is that what should happen and will it be safe to drive.I guess i will need a new solenoid.

Greg, what you describe is synonymous with a leaking solenoid valve and I would assume that yours is faulty, needing to be replaced. What you could do to verify that it's not just co-incidental, is to reconnect the vacuum pipe (locker switch in the off position) drive it a bit with the diff being cold (preferably on a gravel / loose surface) and see if the locker kicks in again. Note that with a leaking solenoid the locker will engage while the selector switch is off and that the green light only will come on.

I would just as a matter of course also remove, clean and replace the diff breather valve since it is a possible problem issue, if not now, later. Better still would be to fit a high level breather and eliminate the issue all together. It's a simple DIY job that shouldn't take more than ½ and hour. I did both mine for about R130 ..... see here viewtopic.php?f=93&t=16855" onclick="window.open(this.href);return false;

I have another problem know , my diff lock wont switch on . I have put a new vacuum solenoid in and it does not seem to help , any saggestions.

Is the solenoid 'clicking' when switched?

Is there vacuum at the diff?

Sometimes there is a little non-return valve on the vacuum line (before the solenoid) .... maybe you put it back in the wrong way around when replacing the solenoid?

Hi Andy
I also have a gearmax difflock on a 93 Sfa,but my problem is that the difflock disengages half way up the obstacle.

offroad nut wrote:Hi Andy
I also have a gearmax difflock on a 93 Sfa,but my problem is that the difflock disengages half way up the obstacle.

You more than likely have a vacuum leak in the lines somewhere ...... a tell-tale sign is that it disengages as the revs drop or re-engages when the revs climb again.

When I rev it cuts off ,and when I reverse it connects again

Hi Andy

I do have vacuum at the diff and the solenoid is clicking in\out. Do you think it may be the diaphram ?

offroad nut wrote:When I rev it cuts off ,and when I reverse it connects again

Huh! Not sure about that problem. Maybe you need to open the diff rear cover and check out what's going on in there .... maybe something worn or the fork bent.

Grego wrote:Hi Andy

I do have vacuum at the diff and the solenoid is clicking in\out. Do you think it may be the diaphram ?

Greg, if you have vacuum it should engage. It could be the diaphragm, but you are aware that the locker won't necessarily engage immediately ..... the 'teeth' need to mesh and for that to happen they need a little 'differential' to line up. You sometimes need a bit of slip on one wheel or otherwise drive in an arc for 2 or 3 metres .... if it still doesn't engage, then I would look at that diaphragm.

offroad nut wrote:When I rev it cuts off ,and when I reverse it connects again

You can sometimes have a loose connection for the indicator lights. And I had this as well, the diff lock would "disengage" on a bumpy incline. I checked more closely and the actual diff lock was not disengaging but the contact for the indicator lamp was dirty so I gave that a clean and replaced a faulty dash switch. Between both those things it sorted out the problem.