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No O/D in 4L80E until 210 degrees

Alvy

By Alvy
in Ask A GM Technician

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Alvy

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Hello again everyone. I posted this problem about a month ago but have had no luck yet, any help would be great. My 94 sierra crew dually with 6.5 T/D has no O/D until it reaches around 210 degrees on the temperature gauge and then it will engage O/D. I have been told that it should do that and also that it's torque converter lock up that I'm not getting and not O/D. I know the difference between the two and also know that this is a probelm and NOT what it should do. I have a feeling that I have it narrowed down to an input to the ECM as far as temperature of the engine goes that the ECM might be reading a faulty coolant temp sensor reading from the t-stat housing and not letting O/D engage until later than it should. After warm up it is fine and has O/D all day. What I would like to know from some one is the resisitance readings of that sensor when cold and then graduating at operating temp to see if my temp sensor for the ECM is bad. I have already tried new coolant and T-stat with no luck. I have also heard that OBDII systems in this truck have an internal trans temp sensor in front of the valve body inside the pan of the 4L80E trans that limits O/D until a specific trans temp is met. Does mine have OBDI or OBDII and if so do I have this sensor? Need some help please due to this is the last problem with the truck that I am having and I have been struggling with it for a while now. By the way, no stored DTC's either. Thanks, Mike

  • 2 weeks later...
Alvy Enthusiast

Alvy

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Posted

OK, so I have replaced the coolant and t-stat along with the temperature sensor for the ECM in the t-stat housing and still have the same problem. I've been told that I should have O/D between 130 and 170 degrees engine temp. Is there a transmission fluid temp sensor in my truck? Again, I know its not lock up that I don't have, it is definately O/D. No stored DTC's either. Please help, thanks, Mike

P.S. Can anyone give me some resistance spec readings for the A and B solenoids in the pan, TPS, and VSS (2)?

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