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3rd Gear Chirper
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2 days ago I got a flashing O/D OFF light and immediately drove it down the street to AutoZone, as I figured the EEC had set a trouble code and the basic scan tool that AZ uses could pull the code. Well their scan tool said no codes were present, and the AZ guy didn't believe me when I told him that the flashing OD/OFF light was done by the EEC and that was how you accessed transmission trouble codes (thru the OBD II diagnostic connector). So the next morning I brought it into the shop at school (Charlotte Vo-Tech) and put the NGS tester on it. That's a New Generation STAR Tester, basically a handheld computer that lets you interact with the EEC. The instructor only had a card for 1999 and newer vehicles, so we set it up for a 99 Town Car. I have a 98 4R70W with the connector re-pinned to work on the 97 EEC harness, as per the article in the WiP forum. The NGS readout showed that the EEC had detected excessive trans oil temperature, and also engine RPM over limit. The RPM over limit fault is my fault, I hit the rev limiter the night before on a manual 2-3 shift. We cleared the codes and they have not returned since...BUT I am concerned about the transmission temps being too high. I have a trans temp gauge, it's a mechanical one, and not directly in line with the flow of oil thru the cooler lines, so I plan to move it soon, either into the pan or find an adapter and move it directly in line with the oil flow to the cooler, preferably the second idea. I have put an instant-read thermometer between the fins of my trans cooler where the oil enters it and get an average reading of about 155*F, which is normal.

My question is, just how hot does the trans fluid have to get to trip the temperature warning code? And is the sensor a thermistor or just a switch? Thanks for any help.
 

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I don't know about the TOT code, someone else can chime in.

But 155 degrees is perfectly normal. As long as its under 200 degrees you won't start burning it up.

JH
 

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286 Posts
Temp sensors (all of 'em) are NTC thermistors, which lower their resistance as they get hotter. There might be a short or electrical leak that is causing the tranny temp sensor to lie to the PCM. The book gives the resistance expected at various temps.

Remember that the cooler flow comes right out of the TC, and can be extremely hot if the TC is running open, even though the pan fluid is still normal.
 
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