ATF fluid temperature sensor

dbeckwith · Post by **dbeckwith** » 30 Mar 2012, 16:48

If anyone has had to replace a faulty ATF fluid temperature sensor I would sure love to hear the circumstances connected to diagnosing the sensor and what the outcome was.

Thanks in advance

turbozutek · Post by **turbozutek** » 30 Mar 2012, 18:52

I had cause to test mine a while ago:

https://www.matthewsvolvosite.com/forums ... =1&t=42460

It wasn't at fault, but that thread should help with how to test it.

Chris...

dbeckwith · Post by **dbeckwith** » 31 Mar 2012, 05:59

Thank you turbozutek for the info. I guess I shouldn't complain too much since the tranny hasn't acted up for months but summer is near and with higher ambient temps just around the corner and that is when the problem starts,(when deaccelerating from 40 mph or higher it downshifts into what I sense as neutral at a stop lite or sign). Then I have to increase rpms to 1400 or so before it will engage first gear. I have done all the things associated with initial troubleshooting to no avail. I even installed an atf cooler thinking that if it is temp related maintaining a lower temp might solve the problem. Alas, no luck. Even though this has turned into a love/hate relationship with this car everything else looks and works perfectly.

Thank you again for your interest and response

Post by **jimmy57** » 31 Mar 2012, 07:21

It is not the temp sensor. The temp input is used for decision if fluid is up to normal temp range and torque converter locking can function. Then fluid temp if it gets to about 260 F the TCM will go into a stage 1 overtemp function where the locking torque converter is used in 3rd gear and possibly 2nd gear. Upshift from first may be early so the TC lock in 2nd can be applied earlier. Locking the TC eliminates the main source of heat generation. Stage 2 overtemp is selected if the temp of fluid goes over 300F and the line pressure is increased drastically causing hard shifts and TC lock is applied immediately upon 2nd gear change as well as 3rd and 4th changes. Upshift light flashes until cooling down to 245 F or so.
Your problem doesn't fit these scenarios.
Your symptoms do fit one of two things: there is a leaking seal on the low (C1) clutch or the side coder of transmission that supports the drum with C1 and has the seals that seal the C1 transfer port on the end cover hub has a worn or broken seal. The fluid thins out when warm and will leak more readily and the increased engine increases pump volume and overcomes the loss and builds enough pressure to apply C1 and it moves off.
Inspection of end cover is the way you'll know if it is an overhaul or an end cover replacement. The end cover R&R is an in-car deal but you do have to lower subframe and eng/trans in order for the end cover to be below the LH frame for access.
DO you have harsh reverse engagement at times?

dbeckwith · Post by **dbeckwith** » 31 Mar 2012, 07:41

Jimmy,

I got a lump in my throat when I read your response. Your explanation seems all too plausible to me

. Once before you had mentioned something about VSS but since I live in a restricted association I wasn't able to investigate. I am planning on renting a garage soon to do some other maintenance on both my cars so I was hoping to get a handle on this. Does it occasionally shift harshly into reverse? Yes

. This said, is there an additive or different type of fluid that might not break down as much when temps rise? Does this rule out the possibility of VSS?

Thanks again so much for in depth explanation

turbozutek · Post by **turbozutek** » 31 Mar 2012, 08:09

I'd agree totally with Jimmy. Some Lucas stop slip might help a little (it keeps the ATF thicker when hot), but the only fix for this will be to replace those seals.

Chris...

dbeckwith · Post by **dbeckwith** » 31 Mar 2012, 08:18

Thanks Chris. I guess I knew the answer but I didn't want to hear it

The car is completely functional. With hot weather coming soon I will just revert back to driving it in 3rd gear. It doesn't act up then. I seldom travel at hwy speeds so other than
miserable gas mileage it should be OK.

Thanks again

turbozutek · Post by **turbozutek** » 31 Mar 2012, 09:11

I dunno man, those that know better than I can confirm it, but I think driving it like that'll kill the box pretty quickly?

Chris...

dbeckwith · Post by **dbeckwith** » 31 Mar 2012, 09:27

Thanks Chris. I should state that in the past year I have driven maybe a thousand miles. I only use the car as a grocery getter. Even though I have developed an affinity for the car putting a lot of money into it isn't a prudent option and since my arthritis has left me unable to do what I might have in the past doing it myself is unlikely.

My next question is, given all the good responses to me post, would changing to a synthetic ATF lower the operating temp of the trans fluid?

Thanks

Post by **jimmy57** » 31 Mar 2012, 11:42

No VSS problem that I can see.
Nothing short of finding the problem and repairing it will fix it. With reverse being harsh the end cover is a greater possibility. The low pressure it has when leaking is slipping C1 and will destroy it if not fixed.