Trans fluid temp abrupt drop in 2nd/3rd - Taurus Car Club of America : Ford Taurus Forum
 
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post #1 of 3 (permalink) Old 10-01-2017, 10:22 AM Thread Starter
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Trans fluid temp abrupt drop in 2nd/3rd

First, Thanks to this resource, and members here for help already in this issue that I have been dealing with..

So, I have a 2005 dura taurus, with a 4f50n - 107,000. It started showing a " check trans" in the message window after driving for 45mins, or so. It did not have any codes, or symptoms. Then, one day, my son had the car out of town, and the problem arose. When I got there to check, it was doing the " shudderring " at engagenent..

I tracked all of the symptoms and dove into the cover. It ended up being a shattered retaining ring for the pump. I scoped the converter, and the splines appeared to be fine - so I went with a rebuilt Valve body to cover the pump issue, update solenoids, and get away from the risk of any small retainer pieces possibly being in a valve passage..


Sooo - I got everything back together, and through to early stages of fluid levels / short drives / increasing heat and longer drives etc. BUT, here is my situation now...

The car / trans seems to be fixed. It operates as it should, and doesn't throw and codes or or problems.

EXCEPT - when I monitor the trans, with Forscan , through the PCM bus for actual gear - trans fluid temp ( TFT ) - trans temp sensor voltage ( TSV ) and trans sensor fault ( TSF )... The numbers all look good -

BUT, when in second or third gear the TFT and TSV will drop off ( 157 to 50ish degrees E.G. )as soon as shift to second and jump right back up as soon as shift into 4th ( right back up to assumed real temp 50ish to 157 E.G. )... but doesn't ever show a TSF or any DTC...

I checked a chiltons PCM / engine wiring diagram, and it appears that the TFT gets it's power from the shared hot for most other sensors, and an isolated return / signal wire to PCM... And the #1, #2, #3 solenoids have a separate dedicated feed and isolated trigger back to the PCM. ...So, it wouldn't appear to be related - or relatable..

I'm kinda lost here..

Anybody got anything or any ideas..???
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post #2 of 3 (permalink) Old 10-02-2017, 07:44 AM
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If the trans is operating correctly, I would not look for trouble where there may not be any.

However, if this is a situation where you really must know for your own peace of mind regarding the Transmission Temp, you will have to monitor the TSV either at the transmission connector, or at the PCM connector. I suspect you will find everything is okay, and the temp readings you are getting are a result of the PCM programming, or the Forscan software. You could also monitor the sensor feed voltage at the same connectors to check for any fluctuations. The TFT has it's own dedicated VREF that is not shared with anything else. you can monitor it at pin 37 of the PCM.

This should keep you busy for a while. Let us know what you find out.

Don
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post #3 of 3 (permalink) Old 10-02-2017, 08:49 PM Thread Starter
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Quote:
Originally Posted by Precision Transmission View Post
If the trans is operating correctly, I would not look for trouble where there may not be any.

However, if this is a situation where you really must know for your own peace of mind regarding the Transmission Temp, you will have to monitor the TSV either at the transmission connector, or at the PCM connector. I suspect you will find everything is okay, and the temp readings you are getting are a result of the PCM programming, or the Forscan software. You could also monitor the sensor feed voltage at the same connectors to check for any fluctuations. The TFT has it's own dedicated VREF that is not shared with anything else. you can monitor it at pin 37 of the PCM.

This should keep you busy for a while. Let us know what you find out.

Don
Thanks Don.. Yea, I'm not going out of my way to create issues, and am aware of overthinking.. but now that this car is going to live an hour away for the next year or two - I'm just trying to cover my bases , and be thorough on the fix..

I did check the sensor voltage as well as the reported temp from the PCM.. they both take a dive as soon as the trans shifts into second gear, and doesn't recover until it shifts into overdrive.. that is what made me try to project my limited experience forward to think that maybe it was an open neutral/ ground.. But, if my info is correct, the solenoids and the sensor don't really share power or trigger / ground..

As long as it's just a glitch - I should be fine , as it shouldn't trigger an overtemp situ as long as it works in O/D ( I assume..)

Was just asking, and looking to see if this condition may have been leading me to a future issue / gremlin that would be easier to address while the car was still local ( as opposed to an hour away ) ...

At this point - the only info that I'm getting is that the PCM may be getting abit tired.. So I'm going to clean connections and make sure that voltage stays up..

Thanks again.. ( last transmission I worked on was dad's Lencos , but that was 40 years ago - and, there weren't any wires..)
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