I know this code is real popular with the older E4OD transmissions. I've searched and searched, but I have yet to find any information that tells what the EEC-IV is looking at [missing] that the the ECU determines that is the code to set.

I can assume that the input speed [engine RPM] and output speed [PSOM] is important. If the signals are ok but the ratios are wrong, there has got to be something slipping and therefore the code could be set, but is there something else? The ECU can't see the line pressure so it's not that [although it will set the pressure to be high if there is a problem]. If there is an electrical fault, I would assume there would be additional codes set.

I have an intermittent issue [only towing and usually 2nd gear or 2-3 shift]. I have a pressure gauge in the cab so I know exactly when the code is set [pressures hover around 200 psi when it does]. Never happens without the 5th wheel installed. I have tested everything before just biting the bullet and shotgunning parts. Everything [except the complete harness] has been swapped out [EEC-IV, hydraulic solenoids, electrical connectors, valve body, front pump/converter valves, converter/twice, MLPS, PSOM, rear diff sensor]. Some of those parts more than once because there are a lot of junk parts out there. I tried my best with OEM parts.

I like testing but until I understand what the EEC-IV is looking at, I don't know what more I can test. I can purchase the QuickShift4 controller that has the option of not going into limp home, but I would rather keep it stock.

Any help would be appreciated. Again, I am looking at the logic what the ECU is looking at to determine how it knows the clutch is slipping.

 

I used to supervise the group that set these codes. I have a fairly good idea of how this code is set.

The EEC looks at engine speed and vehicle speed. It uses math to convert the vehicle speed to output shaft speed. When the trans is in fourth gear and the converter is locked, it compares engine speed to output shaft speed. Output shaft speed must be within 50 RPM of what it is calculated to be, or the code is set.

 

That is what I suspected but when testing, hunches are not as good as facts. I do have a 4.10 differential and it came stock with a 3.55. I believe I have the right settings programmed in the EEC-IV, but I guess I will double check.