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Auto gearbox - won't change up into top gear?

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Steve_C
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PostPosted: Sun Jan 08, 2017 16:37    Post subject: Reply with quote

As I suspected, I wasn't able to locate any other sensors, so if they're there, they must be well hidden.  I also couldn't find any plain yellow wires anywhere.

I did locate a blue and white wire, but this connects to the top of the fan drive unit with a tubular connector



It was quite a loose fit so I've crimped it up anyway, but I don't imagine it will make any difference to the O/D issue.
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Simon_W
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PostPosted: Sun Jan 08, 2017 19:13    Post subject: Reply with quote

Sorry Steve but I've had no time today to experiment. However I'd be very surprised if it was any different to this one on another 2.8 diesel, and I don't think that's much help to you.

http://i219.photobucket.com/albums/cc95/emaxmax/PICT0205.jpg

I guess the other way of checking the theory would be to put an earth on the appropriate pin of the gearbox ECU. I only have a Pajero wiring diagram, but in my experience the same wire colour scheme is used in the Sport vehicles. If so, you are looking for a blue wire with a white stripe going into terminal 7 of the gearbox ECU.  If you haven't got a copy of the Pajero workshop documents let me know and I will PM you with a link to my Dropbox. The gearbox ECU and overdrive switch are shown on pages 4A-82 to 4A-85  (acutal pages 178 to 181 of the pdf.
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Steve_C
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PostPosted: Sun Jan 08, 2017 19:45    Post subject: Reply with quote

Thanks Simon.  That image is useful because it shows three separate temperature sensors, one of which is a double connector like mine (Which appears to be unrelated to the sensor for the gearbox).  I can only find two, which suggests there's a third lurking out of sight somewhere.

I don't have the Pajero workshop documents, so I'd appreciate access to a copy of yours.  I do have a suspicion that some of the wiring may have changed between 2003 and 2006, but logically most of it is likely to be the same.  I'm not sure where the gearbox ECU is located, but something I saw in my searches suggests it's behind the footwell trim panel on the passenger side.  I guess it will show it in the workshop manual.

I'm very grateful to you and Pete for your help with this!
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Steve_C
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PostPosted: Thu Jan 12, 2017 20:26    Post subject: Reply with quote

This might be a dim question, but the Shogun Sport is listed on Parkers as a 4-speed automatic transmission.  Does that mean 3 plus the overdrive, or 4 plus the overdrive?

When I lose "top", I can change into 3rd and the revs don't change.  When all is working, 60mph in top is around 2250 RPM and 40mph is around 1500 RPM.  When I lose top, 40mph is around 2400 RPM but 60mph is close to 3500 RPM.  I'm just wondering if my problem is two missing gears rather than just the overdrive.
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Simon_W
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PostPosted: Fri Jan 13, 2017 2:07    Post subject: Reply with quote

It's three plus overdrive, so it's a four speed transmission.  Top gear is technically an 'overdrive' as the ratio is less than 1:1.    There is also a torque converter lock-up (in overdrive only) which drops the rpm by about 200 rpm when engaged.

From the figures you gave, I can calculate that you are only missing overdrive (and lock-up).  But it doesn't really need a calculation.  If you were missing two gears you would only experience one shift (from 1st to 2nd).  If you put the shift lever in the 2 position you will feel and hear what this is like. It's unmistakable.
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Steve_C
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PostPosted: Fri Jan 13, 2017 20:09    Post subject: Reply with quote

Thanks Simon - I think it was the torque converter lock-up that was confusing me as I didn't have any idea that it was there.  I've knocked-up a speed chart using the ratios that I've found for 1st - 4th and final drive, and the RPM for a given speed in 3rd seems consistent with what I'm getting.

If I can brave the cold tomorrow, I'll get the cover off and have a look at the wires into the gearbox ECU.
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Simon_W
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PostPosted: Fri Jan 13, 2017 22:30    Post subject: Reply with quote

Steve_C wrote:
Thanks Simon - I think it was the torque converter lock-up that was confusing me as I didn't have any idea that it was there.  I've knocked-up a speed chart using the ratios that I've found for 1st - 4th and final drive, and the RPM for a given speed in 3rd seems consistent with what I'm getting.



That's what I did too. What are the gear ratios for your model? I assumed that 4th was 0.705:1 in order for my calcs to work. I'll be interested if that was the correct ratio.
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Steve_C
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PostPosted: Sat Jan 14, 2017 10:42    Post subject: Reply with quote

The ratios listed in the handbook are;
1st gear ratio 2.842
2nd gear ratio 1.495
3rd gear ratio 1.000
4th gear ratio 0.731
Final drive ratio 4.632

The handbook is pretty generic though - for example, it doesn't list my wheel / tyre size and it doesn't make any distinction between ratios for petrol and diesel engines.  I wasn't entirely accurate with my original statement about the RPM, and I monitored it more closely yesterday, so according to my speed chart in 3rd;

40mph = 2144 RPM
50mph = 2680 RPM
60mph = 3216 RPM
70mph = 3753 RPM

These values are pretty consistent with what I'm seeing.  The speed chart is based on nominal tyre diameter, which may not be entirely accurate, but it should be pretty close.
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Steve_C
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PostPosted: Sat Jan 28, 2017 12:50    Post subject: Reply with quote

I badgered my local dealer into contacting Mitsubishi technical for an answer on where the engine coolant temperature switch is, and Mitsubishi came back and said that it's the double connector - which I'm pretty convinced it isn't.

To test this, I drove the car (from cold) with this plug disconnected, and it does still change up into the O/D gear until it's been warm for a few minutes when it stops again.  Therefore, if the gearbox ECU is reliant on a signal from a sensor to enable selection of the O/D gear, it isn't getting it from this one.

One of the guys at work made me up a small loom to connect the plug and sensor, with wires coming from the loom to plug into my multimeter.  With the engine cold and ambient air temperature at -2 degrees and the ignition on, the voltmeter reads 3.49V.  With ambient air temperature at +5 degrees, it reads 3.00V.  When the engine is started, the voltage drops fairly rapidly.  I haven't done enough runs with this setup yet to know what the maximum voltage is that O/D is engaged at, but so far it is 1.42V.  When the engine is fully warm, the multimeter shows a steady 0.47V, +/- 0.01V.  On one occasion, it did select O/D at 0.47V.  All of which is completely irrelevant if this sensor isn't part of the circuit.

I'm inclined to believe that both of these tests rule out this sensor as the cause of the problem.

I'm also inclined to believe that once O/D has been selected, it will stay selected for as long as a suitable engine speed is maintained.  It's only when it drops out of O/D that it then won't re-select it.  Again, if the voltage from that sensor is constant, it can't be that that's causing the issue.

I still haven't located the gearbox ECU, but I haven't really tried after drawing a blank last time.  However, it's feeling less like this is the cause of the problem.  Are there solenoids or something on the gearbox to control the selection of the gears which might be failing?  Or something else that might be fine until it's hot?

I suspect the A/T fluid has never been changed, which I believe should have happened at 54000 miles (I'm now on 78500).  Is it possible that the A/T fluid is just worn out?  I don't really just want to throw money at getting it changed if the problem lies elsewhere - if it needs a new gearbox, I'll just cut my losses and scrap the car.
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Steve_C
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PostPosted: Thu Feb 09, 2017 20:58    Post subject: Reply with quote

Following a chat with a chap at Mitsubishi, I'm slightly better informed, but no further forward.

The wiring diagram supplied by my local dealer which shows the yellow wire is, surprise, surprise, not the correct diagram for my vehicle.  The chances of them seeing my Sport again are diminishing rapidly.

The Mitsubishi fella confirmed that this vehicle from 2002 has an INVECS controlled automatic transmission with a single ECU for both engine and transmission, and the double pin sensor is indeed the engine temperature sensor which feeds the ECU.  His view is that if it's disconnected, the vehicle will run on default settings and assume that the engine is way hotter than it should be.  Either way, if I get the same behaviour with the switch connected or disconnected, it's still unlikely to be that.

His view is also that it's less likely to be a gearbox problem and more likely to be something else, probably engine-related, that's causing the issue.  He thinks that the P0161 sensor fault may be making the ECU tell the gearbox not to change up.  I don't really buy this, but he's not prepared to run any other tests until this fault is cleared and the gearbox oil has been changed.
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peteinchad
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PostPosted: Fri Feb 10, 2017 6:11    Post subject: Reply with quote

Steve_C wrote:

I suspect the A/T fluid has never been changed, which I believe should have happened at 54000 miles (I'm now on 78500).  Is it possible that the A/T fluid is just worn out?  I don't really just want to throw money at getting it changed if the problem lies elsewhere - if it needs a new gearbox, I'll just cut my losses and scrap the car.


I must admit that my first action with autobox problems is to change the ATF.
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Steve_C
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PostPosted: Tue Feb 21, 2017 20:46    Post subject: Reply with quote

Gearbox oil and filter changed at significant cost, no change to the behaviour of the gearbox.

Time to scrap it.
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Simon_W
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PostPosted: Wed Feb 22, 2017 1:55    Post subject: Reply with quote

Steve_C wrote:
Gearbox oil and filter changed at significant cost, no change to the behaviour of the gearbox.

Time to scrap it.


Worth getting it checked out by a gearbox specialist first? It could be something as simple as a failed solenoid in the gearbox or a broken wire. It's an intermittent fault, so unlikely to be any major mechanical problem.
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Steve_C
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PostPosted: Fri Apr 28, 2017 16:47    Post subject: Reply with quote

After 4 months, during which time other people have put a lot more miles on the Sport than I have, the problem has finally been resolved.

I took it to a gearbox specialist who went through all of the standard diagnostics, but he could only find a bad signal from the inhibitor switch.  The part was changed for a new one, which cleared that fault but did not fix the top gear problem.  He was very fair and only charged me the cost of the part - wouldn't take anything for his time because he hadn't resolved the problem it went in with.  His view was that it was probably something to do with the ECU, but by no means certain.

At this point I was ready to drive it into a scrap yard and leave it there, but I made a 'phone call to the garage who changed the gearbox oil and filter (former Mitsubishi dealer) to see if they had any ideas before I gave up on it.  They introduced me to their former Mitsubishi master tech who now runs his own garage, and I decided to book it in for one last attempt at diagnosing the fault.  He re-checked everything that had been done before (all fine), but then determined that he was getting a dodgy signal from the low range switch on the transfer box, effectively telling the ECU that low range was engaged when it wasn't.  Because the ECU though it was in low range, it (correctly) wouldn't allow top gear to be selected.  He disconnected the cable to the switch, and was immediately able to engage top gear.  New switch (MMR246221) Ģ25.96 + VAT, problem solved.

I'm now rationalising what I've spent in getting it sorted - I don't know when or if the gearbox oil and filter were last changed, so that's not a bad thing to have done, albeit sooner than I would have liked.  The inhibitor switch wasn't cheap, but that's another fault fixed.  Everything else was time and frustration.

I would wholeheartedly recommend the guy who did the diagnostics and fixed the problem; Joe at J & M Automotive Ltd in Taplow SL6 0ND - 01628 663833
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Simon_W
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PostPosted: Fri Apr 28, 2017 20:31    Post subject: Reply with quote

Well done. Very glad you've got it sorted.  

Thanks for the recommendation for J&M Automotive. Always good to know who the good guys are.  Smile
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