Overdrive Disengagement

[tussock1]

hello
I am a new member. it took me 2 days to become a member as i m not a computer person. i got help from my son. however, i have got a isuzu bighorn 3.1D 1993 model. my problem is that when i try to drive the van after warming up on cold engine for 2 to 3 minutes the overdrive will NOT engage ie the rev will increase but will not go in overdrive. But when the temp gauge is just about half ie when the engine is all warmed up the beast runs smoothly with no problem. we have changed the following
thermostat
water temp sensor- second hand
transmission fluid sensor- secondhand
flushed transmission- do not know the name of the transmission fluid.
changed 2 solenoid in the transmission
regular service done
tried to locate a garage who can do scan but to no avail. tried 4 places and i was told they do not have scanners for this type of van. even tried isuzu d-max but no luck. i have also bought a secondhand tranny to change but it is on standby. the reason this van suites me well is that i have got a artificial knee and cannot bend a lot so the space in the driver's seat suites well with my knee. can any body help me please.
many thanks

[geeves]

When the engine is cold a special shift pattern is in place raising all the change points This is in place till the coolant reaches 70C which takes a lot more than a few minutes.
You might have an ecu problem causing this to happen at a higher temp than normal but it sounds to be working correctly

[tussock1]

Hello Geeves
Thank you very much for the reply.
Could you please let me know where this ecu is located and where can i buy another one from please OR shall i take the 4x4 to any mechanical shop please