The Mitsubishi Pajero Owners Club®

[Steve_C]

I did a longish run (75 miles) up the motorway - nice and steady at about 60 mph, and all was good.  Car behaved perfectly, sitting at about 2500 RPM

On the way back, it wouldn't change into top gear, so 60 mph was at around 3250 RPM.  When I got off the motorway and came to a stop at traffic lights, it did a sort of "clunk" as it dropped out of gear which it hasn't done before.  Between runs, the car was only sat for a couple of hours, so probably didn't cool down fully.

Any pointers gratefully received.

[Google]

[Simon_W]

No gearbox warning lights coming up? Have you checked the ATF level?

A common reason for the gearbox failing to engage top is a fault in the temperature sender. I don't know the petrol versions, but on my diesel the sender for the temperature gauge has another terminal that goes to the gearbox.  This prevents top gear (overdrive) being engaged unless the coolant reaches 60 deg C.  

If your petrol version is the same, find the sender and locate which wire goes to the gearbox ECU. (Hint: it's the one that doesn't cause the temperature gauge to drop to zero).  Then apply an earth to the gearbox wire.  If it now engages top gear, you've got a faulty sender. If it doesn't, the fault lies elsewhere.  

I am concerned that you felt a 'clunk', which might point to something more serious.

[Steve_C]

No lights coming up on the dashboard.  I haven't checked the ATF level - the manual says I need to drive it around a bit to warm it up, then run through each selector position before removing the dipstick.  A job for tomorrow.

Engine temperature is showing as normal on the dash, and is stable.  Can you point me to where the temperature sender is please - I have no clue on this engine.

[Simon_W]

[Steve_C]

ATF level appears to be mid-way between the two "hot" marks on the dipstick.  It behaved completely normally today, changing up to top / overdrive exactly where I would expect.

I can only assume it was something to do with the longer run yesterday - something (possibly the sender) getting an abnormally long heat soak, compared to its normal use.  I'll have to keep a eye on it.

[Steve_C]

Update: The problem is still present, and gradually deteriorating.  I drove it to work this morning, and it was fine on the motorway (2 miles from home), but started to act up when I was about 4 miles off the motorway and 4 miles from work.  This evening, after 8 miles of A roads from work to the motorway, it wouldn't change up into top, so I was doing >3000RPM all the way home.  I had it plugged-in to a diagnostic machine on Wednesday and no fault codes were present in the gearbox ECU.

There appear to be two temperature senders on the thermostat / water pump housing casting at the front of the engine.  One has a single wire coming from it, the other has two wires.

Simon_W: when you say "apply an earth to the gearbox wire", I don't understand what this will do.  Presumably the sender is either creating an output signal, or is just encountering an increase in resistance as the temperature increases.  If I attach an earth, won't that just confuse the ECU because it won't actually be getting any sort of variable signal?  And do you mean leave the sender cable connected to the sender with an extra wire to earth, or remove the wire from the sender and earth it?  I have no clue when it comes to auto electrics.

[Simon_W]

If it's the same as the diesel, then the sender with the two wires is the one you're looking for.  One of the terminals is connected to the temperature gauge and the other one is the coolant temp sensor for the gearbox ECU.



These senders have an internal resistance which is reduced with increasing temperature.  What you need to do is to remove the double plug from this sender. Then insert a pice of wire (preferably with a spade terminal on it) into the plug in the where the coolant temp sender spade normally goes into.   The other end of the wire you need to attach to an earth somewhere.    The gearbox ECU will now get a very low (near zero) resistance from the sender wire, and think that it's reached temperature.  With any luck it will now allow the geabox to go into overdrive.

Note: if when you've done this the coolant temperature gauge rockets skywards with the engine cold, then you've put the earth into the wrong socket on the plug.

Do you have some wire and a crimp terminal kit?  They are very useful bits of kit, as is a very simple digital multimeter.   All very cheap on Ebay.

[Steve_C]

Thank you Simon, I'm very grateful for the extra details.

I'll have a go at this tomorrow.  I'm pretty sure I've got a spade connector and I probably have a bit of wire somewhere.  I do also have a digital multimeter, although it might as well be a flux capacitor as I've no idea how to use one of those either....

The fact that it gets worse as the engine runs for longer makes me think that the increase in temperature is causing a break in a circuit somewhere, almost like a break in the wire to the sender, although I'd expect this to improve with temperature as any broken ends of wire should expand towards each other, assuming it's a break inside the insulation.  I'd have to say that something around the sender is the main suspect, as this would undoubtedly have been disturbed to some degree when all the belts / tensioner / idler and water pump were changed a few weeks ago, and I didn't notice this problem prior to that.

[Simon_W]

Good luck with it Steve. I have every faith in your ability to use a flux capacitor even if you don't.  

I suspect that you've got a dodgy sender, which will need replacing. It's unlikely to be the wire, although it's not impossible. If the earth trick doesn't work it will probably be the wiring or ECU that's at fault. The gearboxes themselves are almost bullet-proof.

[Mark3]

Overdrive temp sensor on the diesels is a single wire sensor  (front most out of the three under the top hose on the 2.8) the one pictured above is for temp gauge and heater plug ecu.

I would expect the v6 to use the same type of sensor but any single wire sensor will just be an earthing switch (either due to temp or pressure) so find a single wire sensor,  remove the wire and connect to earth,  if your temp gauge to max it's not that one so reconnect and try another... when you find one that don't seem to do anything go for a drive and see if overdrive is working  

[Simon_W]

Thanks Mark. I appreciate your intervention.

Steve, I apologise for my errors but the advice in my first post wasn't too far off the mark. Pun intended.  

[peteinchad]

I don't know if this helps but the circuit diagram for the 6G72 engine is here.




The sensor you are looking for has a single Blue / White wire connected to it - it is this wire you need to connect to earth.


.

[Steve_C]

I think mine is the K96 engine?

[peteinchad]

Maybe they changed the engine for the Sport.

I thought all the V6 engines were the 6G7 series - but I know little about the petrol models. LINK

Edit: I think K96 is the Model number of the truck.

[Steve_C]

This is what I have under the bonnet - single connector on the left, double on the right.



The single connector appears to drive the temperature on the dashboard - when I disconnect the wire, the temperature gauge does nowt.  After mondo googling, I found a way to test the output (with an actual multimeter!  Check me out), which dropped from 22.3 somethings when the engine was cold to about 12.2 somethings when warm.

The double connector is like this;



The wire to the left side of the connector is black, and the one to the right is green / yellow.

Both senders appear to be in a logical place for temperature sensing, unless there's another sender somewhere else with a blue/white wire as per Pete's post.  According to my owner's manual, the engine IS a 6G72 series, like Pete said.