P0715 Transmission Error - Hold light

[Tigmaster]

Hi
I have just bought my Bongo and on the way home experienced the flashing Hold light as well as other issues.
You kind of expect to have some problems on a 23 year old vehicle that hasn't been bought from a reputable dealer.
Mine was a private purchase and i didn't experience this issue when i took it for a test drive.

The Bongo was suffering from a number of issues that resulted in the flashing hold light and when it was on the gearbox seemed to be locked into 3rd and would stall at junctions.
It also stalled when warm on idle, when selecting D or R. This was another issue that was resolved by new plugs, oil change, air filter, fuel filter, vacuum solenoids, Idle control vale clean and throttle body clean. Generally a really good service.
But after all this on my next run, all was fine and then the dreaded hold light appeared.
It was stuck in 3rd again and stalled as soon as I came to a stand still at the junction.
I restarted the vehicle and it was fine all the way home.
2nd run out and it did it all again.

I checked for error fault codes and the transmission found P0715 (transmission input/turbine speed sensor circuit)
After much research this indicated either input or output speed sensors on the gearbox, torque convertor or wiring.

I called a few Bongo specialists and they suggested it would need further diagnostics to really understand the problem.
Although they indicated anything from clean & check sensors/wiring, new solenoids or change the gearbox.
None of them are close to me and my nearest automatic gearbox specialist wanted £88+vat just to road test and run diagnostic test.
Not really sure what else they were going to find without actually working on it.
Weighing up the price of solenoids (£400+ for the V6 petrol) or the price of a 2nd hand box £500 ish, I thought I might as well check it myself first.

I removed the 2 sender units from the side of the box. 10mm bolt and unplug.
The front one was not too bad but the back one was covered in a very dark black substance.
I am aware the transmission fluid needs changing. It was nearly 1 litre below maximum when hot and is a rusty brown colour. Not the worst i have seen on some videos but I decided to top it up first when I bought it. So these sensors have confirmed a drain/refill is required.
With the 2 senders cleaned I researched how to check them.
This is not that easy. You can test the live feed and possibly the return feed but that's not easy when lying on your back with an inch of room between your nose and a dirty gearbox sump. The live feed was around 11 volts which is within spec.
There is a test you can do on the sensors themselves but you need the engine running and hold a spanner near the sensor to test the voltage change. Not a job for today.

Everything was put back together. Fault codes cleared and off for another test drive for over 25 minutes.

Im really pleased to say that the hold light didn't come on and the gears all seemed to select better.
The overdrive appeared to be working and it sat at 50mph at 2000rpm, 60mph at around 2500 rpm.
I tried stopping where possible and it didn't stall once.
When I got home I checked for error codes and there was none.

Hopefully this has resolved the problem.
So I thought I would post this as a new topic just in case someone else has the same issue and it might just help you save a few pounds.

see images for location of sensors (Input at the front, output at the rear)

[Ian]

Thanks for posting this, very useful

[Tigmaster]

After about 40 miles of testing the light starting flashing when I was on the motorway doing about 50mph.
Sure enough when I started slowing down I could feel it was stuck in 3rd. And eventually it stalled at the roundabout.
It started straight away and drove home without a problem or flashing light.
So I thought I would remove the sump and investigate.
I was not shocked but surprised to see how bad the ATF was.
It looked a lightish brown on the dip stick. It was 'Black' inside.

There was barely any crud in the sump cover or any metalic bits on the magnet which was good.
I removed the filter and i would guess that over a cup full of fluid came out along with a fair bit of crud inside the filter.
This has now been washed out and will blow it out with an air line tomorrow.

So heads up anyone who uses the suction method, there is a good chance you are leaving a lot of ATF and crud in the bottom of your gearbox.

I understand my box is post 1999. The earlier ones I read you have to drop the valve body to get to the solenoids.
It looks like the later ones are bolted underneath. Can I unbolt these and clean them &/or check they are working?
Seems like a good thing to do whilst the fluid is out.

The fault code appeared again for the front input shaft sensor.
The sensor appeared to have a fair amount of dark ATF smothering it when I removed it again.
I might just swap it with the rear one and if it comes up as the rear one next time I know the sensor is faulty.
Hopefully a change of fluid will help.
I also disconnected the front pipes that go on the bottom of the radiator. Although there wasn't a great deal that came out of them.

[Tigmaster]

filter cleaned

[Tigmaster]

I removed the solenoids and they were all clean enough.

Shift solenoids measured 3.7 ohms

TCC Lock solenoid measured 57 ohms.
This seems extremely high.
I tried 9v across terminals and no movement. Can i try 12v? i read somewhere this can damage them.
is there anyway i can test it?
Can i get just the TCC solenoid on its own

[Tigmaster]

I have hopefully now resolved the issue.
I purchased a single TCC solenoid from Mazdabongo.com. They were the only ones who could supply it.
This was fitted, filter cleaned, new sump gasket and atf fluid.
The front hoses were also blown out to remove as much old fluid as possible.

Unfortunately the light came back on again. Although it came on at different times, pulling out of a junction, B road, half way down a motorway.
Every time I turned it off and back on again and it was ok.
I spoke to a few Bongo specialists - all indicated possible gearbox rebuild or replacement.

I then decided to swap over the input and output speed sensors on the gearbox as they were both the same.
I took it for a drive and after a while the speedo started dropping even though i was doing 60, then the hold light came on and it locked into 3rd.
Turned it off and back on again - all ok.
pulled over and checked the error codes. I was now getting P0720 (output shaft sensor)

Bingo! its a faulty sensor
A new one from Mazda Europe £110 will take 7 - 10 days, part number was BW01215H2 - now BW36215H2

Bongo spares sent me a 2nd hand one the next day for £50

fitted it today and all appears to be okay after 15 miles of driving

So dont change your gearbox unless you have checked everything.