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Rick, ASE Certified Technician
Category: Car
Satisfied Customers: 6
Experience:  23 years experience, dealer and independent shops
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99 b4000: automatic 4x4 it shifts great..light goes away and it shifts

Customer Question

i have a 99 b4000 pickup.. automatic 4x4 it shifts great... after usually 15-30 miles of driving the over dive off light starts flashing...then it shifts rough....if i pull over turn truck off and back onthe light goes away and it shifts good again for a short period..then the light comes back on and rough again..
Submitted: 7 years ago.
Category: Car
Expert:  Rick replied 7 years ago.
It sounds like the transmission is going into failure mode, probably because of a slip condition or a problem with sensors or pressure control at the valve body.

When the O/D lamp flashes, the transmission control module has detected a fault and commanded a fixed set of parameters for shift strategy. Usually, it will command high line pressure, which is why you notice harsh shifting with the O/D lamp flashing.

The good news is that the transmission control module will store fault codes when this happens. Do you have access to a code retrieval tool?
Customer: replied 7 years ago.

i have had it hooked up and codes were detected. do u need the numbers?there is only 98 thousand miles on the truck. i will call the shop and see if i can get them.

Expert:  Rick replied 7 years ago.
Yes, the codes will help very much. I'll wait for your response.
Customer: replied 7 years ago.
the first time it was hooked up the code was TO455.................the second time about a month later the code came back TO741
Expert:  Rick replied 7 years ago.
The P0455 is an evap leak code, we can ignore that one for the time being.

The P0741 code description is 'TCC engagement or slip condition'. What triggers this code is this:

The transmission has two sensors to monitor the speed of the input shaft (engine side) and output shaft (driveshaft side). When the computer commands drive or overdrive and locks up the clutches in the torque converter (this is done by fluid pressure from the valve body), it monitors both sensors, expecting them to fall within a certain range if the transmission is performing correctly. If the input shaft speed is greater than the computer expects (a slip condition), it will trip the fault code and command failsafe mode to try and get you home.

The three most likely conditions that would cause this code are:

1) Low fluid level
2) A failing torque converter
3) Slipping clutches in the transmission.

My recommendation would be to double-check the fluid level (in park, e-brake set, engine idling), and fluid condition. If the fluid smells burnt or is brown, it's probably time for a rebuild. If the fluid is full and still pink, you need to find a reputable transmission shop to diagnose it. There is a slim chance that a solenoid could have failed, this can be diagnosed with special equipment.

Good luck!