truck transmission diagnostics
truck transmission trouble codes

                        Jatco JR403 Tech Tips

The Jatco JR403E transmission is a computer controlled transmission found in 1988 thru 1998 Isuzu NPR,NQR trucks, GMC, Chevrolet W3500/W4500 trucks, Nissan UD trucks, and Mitsubishi Fuso trucks with diesel engine.

Collapse all | Expand all
Complaint: Transmission wont shift up unless foot taken off throttle or shifts very late, may or may not have TPS code.
Cause: this scenario usually means the throttle cable from pedal to injector pump linkage is loose. depending on how loose is how late may be shifting or not at all. reason for this is TPS is inside cab on pedal assembly, you have pedal and TPS floored and engine is actually maybe only 1/2 throttle. adjust throttle cable so there's no slack in it. this can be adjusted under cab by linkage bracket.
Transmission wont back up, seems like wont shift up at all or very late-actually going 1-3, no second or 4th gears.
Cause: two things may have happened here, both are terminal problems. One: sun gear on shell broke clean off inside unit. Two: sun gear and front planetary are melted which is due to cooler restriction of some sorts. this is very common problem in this unit. filter head for remote filter can be plumbed backwards resulting in dead head situation, or clogged adapter, crimped cooler lines, backwards at transmission, cooler thermostat broken or restricted on Mitsubishi trucks and a variety of cooler related issues. you must have minimum of 1 quart per minute at idle coming out of cooler return line AT transmission when HOT or you will have a repeat of this failure over and over! will not stand any restrictions in cooler system. cooler system is also your lube Ckt for unit so if restricted/plugged you have no lube oil at all and completely melts the inside gear set of the transmission
Vehicle speed sensor code for either speed sensor 1 or sensor 2 in memory but the transmission works fine with no problems.
Cause: one of sensors is dead, Ckt open etc. this will not effect the operation but if the other sensor goes bad etc you will not be shifting at all! should be fixed, there's two of them, ones for backup if other fails.
We offer Free transmission diagnostic help for Jatco JR403 transmissions via E-Mail :Tech Help

allison transmission diagnostics codes
free transmission technical help
Custom Search