91 4l80e trouble code 73

[GMC Josh]

I have searched all over the web and found a lot of conflicting information on this issue. I have a 1991 GMC 3500HD with a 5.7 and 4l80e and 5.13 rear. It has a jasper rebuilt transmission since before i got it. It shifts hard from 1-2, but shifts smooth in all other gears. It always has a Dtc 73 when i check for codes.

The force motor wires ohm at 4 ohms at the pcm connector. No short to ground on either wire. Transmission internal harness was leaking at the plug so i pulled the pan and changed it as well as the filter and force motor. It already has the updated harness. It had the black Holley force motor and the kit that i bought also came with the Holley force motor.

The kit i bought claimed to be for a 91-96 4l80e. I read a pdf for this tranny that said to replace the silver bosch force motor with the black holley one. My pcm is sending 6 volts at 225hz and .7 amps at idle in park. It drops to .6 amps in first gear, but volts and hz drop to zero in any other gear while amperage rises to .9 shortly before the ecm cuts power to the force motor altogether and sets the dtc.

I have even disconnected the alternator to eleminate any chance of electrical harmonics causing this, but still have the same problem.

So at this point, im wondering if i need to get the bosch force motor or does this seem like a pcm issue?

I have attached the pdf that states to use the holley epc solenoid if the trans has the silver "german" epc solenoid.

 

[stutaeng]

I'm no tranny expert by any means, but just watching some of the rebuild videos the statement that it is easy to interchange early with late model 4L80e parts seems to be common, most notably the bushings that carry lubrication.

How long ago was the Jasper unit installed? Do you know if the problem started after the rebuild? Sounds like work was done before you bought it? A line pressure test is probably a good thing to look into.

Maybe someone here can chime in on the parameters for the sensor you are having an issue with...

 

[GMC Josh]

The tranny was replaced before I bought the truck. It looked low milage because when i dropped the pan, there wasn't really any metal dust on the magnet. The fluid was still pretty clean and red. I do agree with you about the interchangeability being common. After more research, im leaning more towards the pcm. It has the 7060 pcm. I agree with you about getting a pressure gauge. Ill try to get one asap. The previous owner seemed to think it has a shift kit, but the code and voltage dropping out to the pressure solenoid has me thinking otherwise. Ive heard about a prom update for the 2nd style solenoid but haven't found any .bin files or details about it.

 

[GMC Josh]

Got it figured out. I changed the ecm and that solved the problem. i thank everyone for the input!