Transmission not changing up to 4th and lock-up not working.

[dickiebongo]

Hi everyone, this is my first post - unfortunately it’s asking about a gearbox (BM715) issue I’m having with my 1999 2.5 diesel. I’ve looked around at posts on related topics but can’t find an answer to exactly what I’m seeing. I’ve tried to check and test as many aspects of the system as I can think of.

Symptoms, with the engine warmed up to normal operating temperature:

• The gearbox changes normally from 1st - 2nd - 3rd gear.
• Regardless of road or engine speed, the gearbox will not change up to 4th gear.
• The torque converter lockup is not working (the revs vary with throttle position when in 3rd).
• Due to the torque converter being unlocked and only being in 3rd gear, I’m doing > 3k RPM at 60 mph.
• The HOLD light is *not* flashing at all.
• The HOLD light is not on continually (I don’t have the button on the gear lever pressed in )

I’ve tried and checked the following:

• I have tried to read the diagnostic codes but unsurprisingly (as the hold light is not flashing) there are none.
• I’ve inspected and cleaned the contacts of all the connectors connected to the gearbox.
• I've tried disconnecting the engine speed and road speed sensors to make sure I do get fault codes when these are not connected.
• I have checked the electrical resistance of the solenoids, they are all within spec.
• I have removed the valve body and tested the solenoids with an airline at 60psi, then applying 12v, they all appear to be working correctly (as well as can be determined by such a crude test).
• After rinsing the filter as well as I can (I don’t have a spare to hand and it looked ok), reassembling and filling with new fluid, the symptoms are unchanged.
• The engine temperature sensor appears to be giving a reasonable voltage reading at the ECU pin [2N]. 2.25V when cold and 0.6V when hot.
• The road speed sensor appears to be giving a reasonable signal at the ECU pin [2G].
• The gear changes, such as they are, feel very precise and are nice and smooth.

I have also looked at the signals on the solenoid output pins of the ECU [1E, 1F, 1H, 1J, 1I], the results are interesting and might point to an issue somewhere. The shift A and shift B solenoid outputs appear to be correct and correspond sensibly to the states of the first 3 gears.

Link to ECU pin connections (google drive)

I’m not sure what the “all running clutch” (translated from the wiring diagram using google translate) solenoid is supposed to do [1J] but it does seem to switch cleanly when you put the car in gear (or was that when you start moving I can’t remember now I come to write the post - anyway it looked kind of sensible).

The lock-up clutch solenoid output pin [1I] is doing something that seems to me to be very strange indeed, as soon as the ignition is switched on it outputs a pulse at 51Hz, this doesn’t change in frequency or duty while driving [channel B in the scope image linked below]. This doesn’t look right to me?

Link to lock-up solenoid signal scope image (google drive)

The line pressure solenoid pin [1E] is also doing something that seems strange to me, it’s got the same 51Hz output that remains unchanged under different driving conditions, apart from the fact the signal only appears once the engine is doing more than roughly 1700 RPM [channel A in image linked below, seen to start pulsing as the revs increase]. This doesn’t look right to me either?

Link to line pressure solenoid signal scope image (google drive)

I should add that the scope probes were set to 10x, in case anyone looks at the voltage levels and thinks they are a little low.

Has anybody else seen this sort of thing or have any other ideas. I suspect an issue with the ECU, what do you guys think? I probably need to speak to a specialist, any recommendations? Reading previous posts it looks like I want to get in touch with Alacritys (George)?

Many many thanks in advance for any help anyone can provide.

[mikeonb4c]

I was going to suggest Alacrity (Geoff) as the best person to speak with if you can get hold of him. You're already streets ahead of a non techie like me. Is the throttle position sensor in the list of items tested? They've been known to cause issues before.

[Flanners]

Just found this advice/post from 2014, from the experience I had with poor shifting a tweak/small movement of the TPS completely cured the issues I was having with the auto box and returned the shift performance,enabled proper hook up again and good mpg:

'Does it have gears 1-2-3 & are they shifting late? If it does & they are it could be the TPS is way out of adjustment after the head issue. It is this & the output speed sensor that determines shift points. No codes only mean there are no ELECTRICAL issues. Dirty connections can be a cause but I would expect to see the HOLD light flashing as it would cause an electrical circuit fault.

If it were here - & it aint never going to be clearly, I would put a set of test lights on the external solenoid wiring to see it the ECU is commanding 4th (only after checking the TPS), if the lights indicate it is then you have an internal issue - possibly solenoids hydraulically failed - if the lights don't confirm 4th gear commanded then your issue is external.'

From my short time of ownership, the small issue I had and then reading this Forum, the shift issue is a problem for many owners, invariably many of the solutions have not been purely mechanical (it appears many owner's have been persuaded to needlessly change ECUs, gearboxes, drain the fluid etc). What is clear is the auto box is very strong and has good longevity. What seems more prone to cause issues is the TPS/electrical.

[dickiebongo]

Thanks for your replies.

I discounted the TPS as it's changing at what appear to be the correct points (as it was when it was working) in gears 1-2-3 and it kicks down too. I'll put a scope on the TPS and see what the signal looks like and how clean it is.

Regarding the solenoid outputs, I've probed all of the outputs while driving,two of them are producing that weird 51Hz output (see original post for details), the others look sane.

[dickiebongo]

SOLVED (FINGERS CROSSED):

First an update on the signals I am seeing on the lock-up clutch solenoid [1I] and the line pressure solenoid [1E] - these outputs *do* appear to be PWM modulated, now I've seen the unit working correctly with the scope connected I can see the duty cycle of the 50Hz output changing with throttle position, and I can see the duty of the lock-up clutch solenoid change (from 6% to about 90%) when the torque converter locks-up. So that 50Hz output from the ECU is normal.

So what did I change to "fix" it (hopefully it will stay fixed) - Well, it looks like there's a relay, fitted aftermarket as part of the campervan conversion, that is energised when the ignition is switched on, this provides power to some of the circuits in the car from the main battery, so they are powered even if the "camper area" power switch is off. While the relay was being energised with the ignition it was dropping out during starting even though the starter battery is fully charged and in good condition. I changed the relay, which solved this issue and the ECU started to behave itself again. So It looks like the power to the ECU is connected through this relay in the modified wiring regime. Bit of an odd one.

Of course it's entirely possible that what's actually happened is that I've wiggled a connector with all the messing about I've been doing and now it's working again. I guess I should swap the relay back and see if the problem reoccurs, but I haven't tried that yet (I like it in it's new working state ).

Many thanks again to those who replied , and I hope the information in the original post and the update about the PWM signal comes in useful to someone in future.

[mikeonb4c]

Excellent. Fingers crossed you're sorted.

[dickiebongo]

I should have added that the TPS signal at the ECU looked ok, it's reading ~1V when throttle closed and ~4V when throttle open. Not sure what the voltages are supposed to be but that looked sensible at least. The voltage changes smoothly over the range too, no jumps or spikes.

I might give the TPS an adjustment to see if I can drop the RPM of change points a fraction, I'll mark it where it is in case I mess it up!

[WestyK]

Thats really good info.
I am trying to get my head around how the box works and whats normal, may be what can be modified or adjusted.

I dont think I have a problem generally as it seems fine most of the time I just feel its a bit late to change up and worse a but quick to kick down.
This is mostly noticeable when on twisty A roads or up and down hills when your doing a modest speed where it could probably handle staying in top. I just think it would be better staying around 2000-2500rpm where most of the toque seems to be instead of revving up to 3000-3500 when there is just a modest amount of throttle.

Its even more annoying when towing where you need the toque and its always revving too high and getting no where.

Dont get me wrong. Its not really bad or even that annoying just think it could be better and I like making my cars better if I can.

[Flanners]

On twisties and up and down dale I use the 'Hold' button, really useful. I too keep the van at 2500-3000rpm on hills, relatively slow but just plods along.

[dickiebongo]

I agree, it does seem a bit keen to change down, I've not tweaked the TPS yet to see if that helps. I'm not sure how much scope there is to make a massive difference with the minimal amount of adjustment available on the TPS.

A word of warning - If you ever decide to play about with something to "frig" the road speed and TPS inputs to the ECU in order to adjust the change points then beware that the gearbox *looks like* (this is just speculation on my part based on the PWM signal sent to the line pressure solenoid under different throttle position conditions) it's also using the TPS to regulate the oil pressure used when actuating the clutches (to produce smoother changes). Fooling the ECU into thinking the throttle is not as open as it really is might be might cause the clutches to start slipping under the higher than expected load. As I say this is speculation, partly based on what I saw when diagnosing my issue with the Bong and partly based on my experience with Range Rover classic gearboxes and what happens to them when the kick-down cable snaps (also regulates the line pressure)!

[Flanners]

When I purchased the van I had never driven an auto box, so was almost unaware that when it went into 2nd the revs would rise (over rev) to 2500-3000rpm then change, this was with very small amounts of pressure on the accelerator, if I accelerated away the problem did not happen, I also noticed that it seemed not to be happy when to lock-up and when not to when cruising and would keep messing about, the mpg was dire too. I tweaked the TPS positon about 5mm and this was too much, after a couple of runs and tweals having marked the initial position, I settled on a about 2mm of adjustment, this cured my issue completely and the van has been spot on ever since. My van has circa 42K miles on it from new so I was not expecting it to be a problem.

[dickiebongo]

When I purchased the van I had never driven an auto box, so was almost unaware that when it went into 2nd the revs would rise (over rev) to 2500-3000rpm then change, this was with very small amounts of pressure on the accelerator, if I accelerated away the problem did not happen, I also noticed that it seemed not to be happy when to lock-up and when not to when cruising and would keep messing about, the mpg was dire too. I tweaked the TPS positon about 5mm and this was too much, after a couple of runs and tweals having marked the initial position, I settled on a about 2mm of adjustment, this cured my issue completely and the van has been spot on ever since. My van has circa 42K miles on it from new so I was not expecting it to be a problem.

Thanks for the info, I'll definitely give the TPS a tweak, sounds like you can make quite a positive impact with quite a small adjustment.

[SimonD]

SOLVED (FINGERS CROSSED):

First an update on the signals I am seeing on the lock-up clutch solenoid [1I] and the line pressure solenoid [1E] - these outputs *do* appear to be PWM modulated, now I've seen the unit working correctly with the scope connected I can see the duty cycle of the 50Hz output changing with throttle position, and I can see the duty of the lock-up clutch solenoid change (from 6% to about 90%) when the torque converter locks-up. So that 50Hz output from the ECU is normal.

So what did I change to "fix" it (hopefully it will stay fixed) - Well, it looks like there's a relay, fitted aftermarket as part of the campervan conversion, that is energised when the ignition is switched on, this provides power to some of the circuits in the car from the main battery, so they are powered even if the "camper area" power switch is off. While the relay was being energised with the ignition it was dropping out during starting even though the starter battery is fully charged and in good condition. I changed the relay, which solved this issue and the ECU started to behave itself again. So It looks like the power to the ECU is connected through this relay in the modified wiring regime. Bit of an odd one.

Of course it's entirely possible that what's actually happened is that I've wiggled a connector with all the messing about I've been doing and now it's working again. I guess I should swap the relay back and see if the problem reoccurs, but I haven't tried that yet (I like it in it's new working state ).

Many thanks again to those who replied , and I hope the information in the original post and the update about the PWM signal comes in useful to someone in future.

Hi Dickie,

Interesting thanks.

I'm trying to trace a similar problem, and there seems to be so many possible solutions to potential problems.
My error code sems to be: 63 'TCC lock up solenoid valve' (which i assume to be within the sump with the shift solenoids etc).
Likely expensive and way beyond my skills, so I'm keen to investigate everything else possible 'easier' first - wiring connectors , relays.

We had just had the ATF changed before the hold light began flashing (was noticed after about 50+ miles at first and now under two to get it going)
I cannot see a link between the two events, but maybe something was wiggled dislodged at the time.

Anyway, I digress, apols! - I would just like to know how to identify the relay you mention, so I can change it?

Ours is a conversion also.

[dickiebongo]

Hi Simon,

Sorry for the delay in posting back, I've been away, in the Bongo (a new thread to follow regarding a new issue but enough of that here).

This image shows the location of the relay on my van:

Link to shared image of relay location (google drive).

However I suspect that your issue is not the same given there's a valid fault code. From what I understand (so far) the system can detect electrical faults in the system and will in those instances generate fault codes. If it's flagging up an issue with the solenoid then I suspect there's an electrical fault somewhere in that circuit.

There are some electrical plugs and sockets on the offside of the gearbox, one of those (the larger of the 3 IIRC) connects to the solenoids in the gearbox. If you're confident in disconnecting them it might be worth cleaning them with some contact oil or similar (careful not to break the clips, they can go brittle):

Image of gearbox connectors (google drive)

You can find wiring diagrams here so you should be able to determine which wire goes to the lock-up solenoid and test the resistance with a multimeter, I can't remember which have what resistances but they are within the 15 to 40 (ish) ohms range (depending on which solenoid it is) I did find the actual spec values somewhere but didn't save the link, some googling about should find you that info but I'd just see what they are if it's open circuit then you know you've got an issue without knowing the exact spec resistance. I would also find the correct pins on the ECU (located behind the glovebox and nice and easy to get to) socket and test the resistance from there as well as at the gearbox connector, to rule out any issues with the loom.

If the worst comes to the worst and the solenoid needs changing this diagram should give you some idea of what's involved.

[dickiebongo]

Just to add, the valve body comes out in one piece, don't take it apart/split it (apart from removing the broken solenoid of course). This is what it looks like when removed, you can see some of the solenoids on the right hand side:

Bongo AT Valve Body

Those 3 springs you can see on the top are from the accumulator chambers and have to be balanced in the correct place on the circular areas on the left of the image while the valve body is put back on the gearbox, I suggest getting someone to help with this as it's a complete pain! Also the springs are different rates and sizes so have to go back in the correct places, they will only fit correctly in the correct holes so don't panic if they all just fall out before you can see which one is which.