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sprinkles08, ASE Certified Technician
Category: Transmissions
Satisfied Customers: 23110
Experience:  Chrysler/Dodge/Jeep master tech ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans Specialist
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I am trying to diagnose why My O/D off and Trans Temp lights

Customer Question

I am trying to diagnose why My O/D off and Trans Temp lights come on but trans does not feel warm. I have replaced the governor pressure sensor/trans oil temp sensor. I don't think I have a wiring problem, the temp sensor resistance is the same @ the connection at the trans housing and at the PCM. I'm sure I could replace it with a solid resistor to allow overdrive to function but I'd like to determine what temperature the computer is seeing (based on the voltage on the temp sensor circuit) and see if it's actually too warm somehow or if this is related to another problem
Submitted: 1 year ago.
Category: Transmissions
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

Either it's seeing an incorrectly high temperature signal or the trans is actually overheating. It wasn't uncommon for the drainback valve to stick closed or the cooler to become restricted and cause actual overheating, but this would happen after driving long enough for it to actually overheat. If the problem happens shortly after starting and actual overheat isn't possible yet then it's going to be an electrical issue. If if it's an electrical issue then it's either the sensor or wiring.

Have you checked for fault codes?

Customer: replied 1 year ago.
There are no trouble codes. I don't think it's a sensor as I have already replaced it with no change. I don't think it's wiring between the sensor and the pcm as the values measure the same. At the moment the O/D off first illuminates I measure a voltage drop of 2.57V across pin 1 connector A (trans temp sensor) and pin 4 connector B (sensor ground) at the pcm. I would think this is well within range of a typical 5v signal, resistance across the sensor is 2010 ohms. I'm wondering if there is a chart which shows the range of acceptable sensor readings and the temperatures that correspond to them?
Expert:  sprinkles08 replied 1 year ago.

There isn't a chart that shows resistance versus temperature as a scan tool is used to diagnose the system.

If the trans isn't actually overheating then you have a wiring or sensor issue. It's either actually overheating or an incorrect temperature signal is causing the PCM to think it's overheating when temperature is actually ok.

Does trans temp show the same as ambient and coolant temperature after a cold soak?

What does it show when the lights come on?

Has temperature been checked at the pressure line leaving the trans using an infrared thermometer while the lights are on?

Customer: replied 1 year ago.
i have not had access to a scan tool that will read the trans temp, i also do not have an infrared thermometer. still waiting until a friend with these tools makes it over to help. the trans pan is never hot to the touch. since the voltage / resistance is the same at the trans and at the pcm, that wiring is not causing the problem. I replaced the sensor ^^ and no change. I have no dtc set. I did some research and see that the sensor should have approx. 1000 ohms resistance at room temp. The new one has 1.6k. thats pretty close right? I can't imagine that there is no documentation regarding the trans temp system operation ex: '@ 3.0 v o/d is locked out, @ 3.4v trans temp light illuminated. I see a range of 1.55 to 3.76v based on when high and low signal DTCs should set. my voltage is always in the low-mid 2's Based on this I believe the pcm Is receiving a good signal. I swapped the pcm and no change. I then figured there could be an issue with the cluster, swapped that out and no change. At this point I think there must be a wiring problem somewhere else but I don't know where to look
Customer: replied 1 year ago.
the dash reads 'no bus' in the odometer display and abs light is on, not sure if either of those things could be related but figured i'd mention it.
Expert:  sprinkles08 replied 1 year ago.

Does the problem only happen after driving for an extended period or will the trans temp light come on shortly after a cold start?

Customer: replied 1 year ago.
After a*****or 15-20 minutes not driving. When o/d off comes on trans tempt will be on within about a minute. Once they comes on I have to let it sit for probably 6 hours or more for them to not be on when I turn the key on
Expert:  sprinkles08 replied 1 year ago.

Has the cooler been flow tested? If so what were the results?

Customer: replied 1 year ago.
Cooler flow has not been tested, is there a DIY procedure for that or should I just point the return hose at a bucket, start it in neutral, and see if fluid comes out?
Expert:  sprinkles08 replied 1 year ago.

Drive it until it's indicating overheat. With the vehicle properly supported and the return line ran into a container, start the engine and measure the amount of return flow for sixty seconds in neutral.