‘15 A/T: Weird temperature reading
12-20-2019, 03:55 AM
#1
JK Enthusiast
Thread Starter
‘15 A/T: Weird temperature reading
Are there two separate transmission temperature senders on automatic transmission equipped JK’s? I made an odd discovery yesterday while in traffic. I had scrolled through my dash display options and the display was reading transmission temperature. I was running along at around 168°. I stopped at a long red light and put it into neutral. After a bit I looked down and saw the display was reading 215°. After I took off from the light it switched back to 167°. Once I got to my destination and put it in park it switched to 210°. My curiosity got the best of me and I played with it a bit. If the transmission was in park or neutral it would read in the 210° range. If in drive or reverse it would read in the 165° range. I’m not talking about a temperature creep. The reading would change like you were flipping a switch.
So either the reading is taken from two different sensors depending on the gear selection (which makes no sense to me) or there’s something screwy with my electrical system. Anyone have the answer? Perhaps I can inspire another A/T JK owner to experiment for me to see if theirs acts the same way?
Thanks,
‘Tom.
So either the reading is taken from two different sensors depending on the gear selection (which makes no sense to me) or there’s something screwy with my electrical system. Anyone have the answer? Perhaps I can inspire another A/T JK owner to experiment for me to see if theirs acts the same way?
Thanks,
‘Tom.
12-20-2019, 04:51 AM
#2
JK Jedi Master
This was quoted and posted a few days ago, from the 2012+ service manual:
"The TCM monitors a contact switch wired in series with the ATF temperature sensor to determine Park and Neutral positions. The contact switch is open in Park and Neutral. The TCM senses transmission temperature as high (switch supply voltage), confirming switch status as open. The TCM then broadcasts a message over the CAN bus to confirm switch status. The engine controller receives this information and allows operation of the starter circuit."
Some people say the temperature reading goes to engine water temperature when the transmission is in Park or Neutral, which doesn't quite agree with the above quote.
A good experiment would be to see if the Park/Neutral temp reading is actually the same as the engine temperature reading.
"The TCM monitors a contact switch wired in series with the ATF temperature sensor to determine Park and Neutral positions. The contact switch is open in Park and Neutral. The TCM senses transmission temperature as high (switch supply voltage), confirming switch status as open. The TCM then broadcasts a message over the CAN bus to confirm switch status. The engine controller receives this information and allows operation of the starter circuit."
Some people say the temperature reading goes to engine water temperature when the transmission is in Park or Neutral, which doesn't quite agree with the above quote.
A good experiment would be to see if the Park/Neutral temp reading is actually the same as the engine temperature reading.
Last edited by ronjenx; 12-20-2019 at 04:57 AM.
12-20-2019, 12:06 PM
#4
JK Enthusiast
Thread Starter
This was quoted and posted a few days ago, from the 2012+ service manual:
"The TCM monitors a contact switch wired in series with the ATF temperature sensor to determine Park and Neutral positions. The contact switch is open in Park and Neutral. The TCM senses transmission temperature as high (switch supply voltage), confirming switch status as open. The TCM then broadcasts a message over the CAN bus to confirm switch status. The engine controller receives this information and allows operation of the starter circuit."
Some people say the temperature reading goes to engine water temperature when the transmission is in Park or Neutral, which doesn't quite agree with the above quote.
A good experiment would be to see if the Park/Neutral temp reading is actually the same as the engine temperature reading.
"The TCM monitors a contact switch wired in series with the ATF temperature sensor to determine Park and Neutral positions. The contact switch is open in Park and Neutral. The TCM senses transmission temperature as high (switch supply voltage), confirming switch status as open. The TCM then broadcasts a message over the CAN bus to confirm switch status. The engine controller receives this information and allows operation of the starter circuit."
Some people say the temperature reading goes to engine water temperature when the transmission is in Park or Neutral, which doesn't quite agree with the above quote.
A good experiment would be to see if the Park/Neutral temp reading is actually the same as the engine temperature reading.
I love my Jeep. But there are certainly some quirks like this that I could live without.
Thank you for finding & sharing this.