Yaris Verso Auto won't engage overdrive

[Yarso]

My Yaris Verso 1.3 Petrol is 15 years old and has given almost no mechanical faults through the whole of its life so far but... it has just stopped engaging overdrive 4th on the auto box - which makes it Ok still around town, but it's going to scream its nuts off when I take it on the motorway!

For the last month or so it has been only intermittent in engaging, so a week ago I replaced the transmission fluid (correct Aisin TypeIV fluid used) on the basis that it would either kill or cure - and sadly I got the former...

I believe one possible cause could be the coolant temp sensor at fault, because cold coolant should inhibit overdrive - but the blue "cold engine" warning light on the dash goes out as normal after a short drive, so I don't think it's that. Can anyone suggest any other possible causes?

I've yet to try it, but I should be able to get Carista running on a tablet, connected to an OBDII bluetooth dongle - are there any diagnostic tests that could be done with that?

[Madasafish]

13 hours ago, Yarso said:

My Yaris Verso 1.3 Petrol is 15 years old and has given almost no mechanical faults through the whole of its life so far but... it has just stopped engaging overdrive 4th on the auto box - which makes it Ok still around town, but it's going to scream its nuts off when I take it on the motorway!

For the last month or so it has been only intermittent in engaging, so a week ago I replaced the transmission fluid (correct Aisin TypeIV fluid used) on the basis that it would either kill or cure - and sadly I got the former...

I believe one possible cause could be the coolant temp sensor at fault, because cold coolant should inhibit overdrive - but the blue "cold engine" warning light on the dash goes out as normal after a short drive, so I don't think it's that. Can anyone suggest any other possible causes?

I've yet to try it, but I should be able to get Carista running on a tablet, connected to an OBDII bluetooth dongle - are there any diagnostic tests that could be done with that?

The coolant temperature sensor controlling the ECU running of the gearbox is entirely different from the sensor which controls the temperature coolant light..

[Yarso]

Thanks - that's interesting. I'm wondering if an app such as Torque will let me see the data that it's generating as the box warms up? I doubt it though - never had much luck with "custom PIDs" on other cars.

Are you aware of any diagnostic tools that would let me read the data via the OBD port? Otherwise, I guess I'll have to find the sensor and test it with a meter - do you know where I should be looking?

At present, the only error code being logged relates to the Throttle Position Sensor, and that's because I've just changed it and the one I've replaced it with doesn't seem to be fully compatible - but I don't think that's the cause, as the intermittent O/D issue started before I touched the TPS.

[Madasafish]

You need an all singing and dancing reader..not a generic one.. Not cheap..

[furtula]

Why dont you just get a Techstream cable for 10-15 GBP from eBay and like, like the rest of us, and you get full access to diagnostic data, or am i missing something here?

 

[Yarso]

7 hours ago, furtula said:

Why dont you just get a Techstream cable for 10-15 GBP from ebay and like, like the rest of us, and you get full access to diagnostic data, or am i missing something here?

 

No you're not - I'm completely new to Toyota ownership, as the car was owned by my late father up until recently - so I don't know anything about the diagnostic tool options.

I'll have another check with Torque later today, as that has an option which scans for manufacturer-specific PIDs - though it did not seem to help much with my VW T5.

If no luck there, I'll have a look at the Techstream product, though Windows-based tools are not ideal for me, as I don't use Windows!

Thanks for the advice - I'll let you know how I get on, if I make any progress. I hope so, as I can't justify a full auto gearbox rebuild on a car that's only worth £600 - though I don't want to scrap it if I can help it...

[Yarso]

Well - Torque will display the gearbox temp (using Method 2, whatever that is) and it looks Ok - just did a short test run and it started at ambient and slowly went up to 44 degrees after 5 minutes driving, which looks believable.

One other thing I have yet to test - does the Engine Management light being on suppress Overdrive? I'm starting to think that maybe it does. So I just need to fix the TPS, turn off the EML and test again...

[Yarso]

Ok - I should have remembered the old rule: "If it's not completely broken yet, mess about with it a bit until it is".

The problem was self-inflicted. Buying a cheap TPS from Poland caused the EML to come on permanently, and - it seems - the EML inhibits overdrive.

Putting the old TPS back and clearing the fault code means that O/D now engages properly! The car is rather more interconnected electronically than I thought it would be...

[stantheman1]

Thanks for the update, could be useful to someone with similar issues.

[Yarso]

Just hope they are a bit less dumb than me and make the association quicker!

I feel even dumber now I've looked at the linkage, because there was quite a large amount of slack on the throttle cable - the car had a minor front-end during my Dad's ownership and it may have been caused then. Taking the slack out probably means that I didn't need to change the throttle sensor anyway. Oh well, live and learn...