Flashing O/D, weird situation

[lrwjr1964]

I hope someone can help me with this. 2 weeks ago My O/D started flashing and the tranny went into it's safe mode. I stopped by a tranny shop and they said the tranny was fine but they got the code for Coolant Temperature Sensor out of range. Does this sensor tie into the PCM and operation parameters for the tranny? I am gathering that since the coolant is also used for the tranny cooler the temp has to be monitored so that if you run out of coolant you won't burn up the tranny and it goes into safe mode thus activating the flashing O/D. Has anyone else had this problem? All replys welcome.

 

[IZwack]

To my limited knowledge, the transmission doesnt have any "coolant" other than its own fluid (ATF). I don't think the transmission is tied in to the engine's coolant system as the engine's coolant sysem only serves to cool the engine.

 

[lrwjr1964]

I just looked in the haynes manual and there are 2 small lines that connect to the radiator and it's for the cooler for those x's with auto trannys. Well I am going to replace the coolant temp sensor since that's the code the tranny shop got. I might even get a tranny and radiator flush.

 

[IZwack]

I just looked in the haynes manual and there are 2 small lines that connect to the radiator and it's for the cooler for those x's with auto trannys.

Right, but this cooler line and the little radiator located at the front of the engine's radiator is dedicated just for the transmission. The transmission and the engine do not share fluids at any point.

 

[90ranajo]

I don't think the transmission is tied in to the engine's coolant system as the engine's coolant sysem only serves to cool the engine.

Yes and no. Your main tranny cooler is a oil to water cooler located in your radiator side tank. The engine coolant serves to warm the tranny fluid upto operating temp and to maintain it at that temp.

Does this sensor tie into the PCM and operation parameters for the tranny?

Yes and I don't know. Yes its tied into the PCM to aid in control of fuel mixture; but does it do anything for the tranny, I don't know.

 

[lrwjr1964]

Well some how the two coincide. The coolant sensor throws an out of range code to the PCM and that throws the tranny into safe mode. What the hell is going on. I reset the computer Monday night cause it came on, drove it and it was fine. Drove it ealier and it was fine until evening. then it came on again. I did smell the slight hint of antifreeze for a second then it went away when I turned my heater on. I noticed when the O/D light came on the hot air dipped slightly then it was hot again. Why does this have to happen now when it's cold as hell outside!!!!!!

 

[90ranajo]

Have you checked your heater core? If you smelled antifreeze and a loss of heat, your heater core may be leaking slightly.

 

[lrwjr1964]

I got my answer from Wells counter points. Here is what the PCM uses input from the coolant sensor to control:

It also uses input from the coolant sensor to
regulate the operation of many other important
functions, including:
• Start-up fuel enrichment on fuel-injected
engines. Injector pulse width is increased to
create a richer fuel mixture when the coolant
sensor indicates a cold engine.
• Spark advance and retard. Spark advance is often
limited for emission purposes until the engine
reaches normal operating temperature.
• EGR flow is blocked while the engine is cold to
improve cold driveability.
• Canister purge does not occur until the engine is
warm to improve cold driveability.
• Energizing the electric heater grid under the
carburetor on older engines to improve early fuel
evaporation when the engine is cold.
• Operation of the throttle kicker or idle speed
when the engine is cold.
Transmission torque converter clutch lockup
when the engine is cold.
• Operation of the electric cooling fan (if a
separate fan thermostat isn’t used) when a
certain temperature is reached.

Now I know why the O/D light comes on. So it is the sensor. Thats why i love wells counter points. I forgot all about this site. Thanks to all who gave input. Much appreciated.

Here is the link:
http://www.wellsmfgcorp.com/counterpoints/Counterpoint2_2.pdf

 

[IZwack]

Thats fascinating

 

[Glacier991]

Sorry, just got here. The transmission uses a strategy to warm up the transmission a little faster. Ya see, the torque convertor is a BIG producer of friction heat when it is not locked..... so when the engine is cold, the computer inhibits torque convertor lockup to aid in heating the transmission.

As for sharing radiators... within your radiator is a smaller one and the transmission fluid is run through there... from there it will go to an external one if you have it, and then back to the trannie. In truth, in most cases this serves a greater purpose in helping heat ATF when cold than cooling it when hot.

A leaking internal radiator will bleed ATF into coolant when the engine is hot, and as it cools it will leak coolant back into the ATF. Fortunately this is a VERY rare occurrence. Coolant in ATF is death to a tranny.

I'll say it again. In a fully computer controlled tranny, many of the problems people experience are related to bad computer inputs, NOT mechanical damage to the tranny.

And WellsCounterPoints.... a wonderful wonderful resource. I printed them all and keep them in a binder updating them every year or so.

 

[lrwjr1964]

Well the Coolant temp sensor was replaced yesterday. No O/D light today. And the x runs a lot better. It even heats up faster. So i will keep my fingers crossed.

 

[lrwjr1964]

Update!!!!!

Well boys and girls, the problem still exist. I have noticed one thing though. The O/D light does not come on if I let the X warm up for 15 to 20 min. The other day when the O/D light started blinking the air coming out of the heat vents was luke warm. I felt the radiator and it was luke warm to the touch. mind you this is after 20 min of driving. The lines for the tranny cooler was luke warm. Well I stopped at Autozone, and disconnected the battery. 5 min later when I reconnected it the heat was blazing and there was no flashing O/D. So now I am starting to believe that there is something wrong with the system not letting the tranny oil heat up. Now I heard another guy on here saying he had the same problem and it turned out to be that his altenator was about to go out. Mine is making an intermittent chirping sound and yesterday when I put my turn signal on the needle was bouncing with the pulse of the turn signal. I hope this is not the end of my X. So once again any suggestions would be appreciated. Also if your supposed to check the tranny while the truck is running my fluid is way above the max line. And I mean way above.