replaced encoder motor - selector 2HI light just flashes!

[njohns]

Okay, I'm stumped...

I decided to replace my encoder motor, which I believe may be flaky (e.g. 2HI and 4HI are okay but I have A4WD issues). I ordered and installed a new Dorman motor, which seemed very straight forward.

However when I was done and turned on the key the 2HI selector light just flashed for like 30 secs and then went out. I don't get a "Service 4WD" light and if I turn the selector to another position it will do the same thing (i.e. flash for 30 seconds and then goes dark). Listening from below the motor is totally silent (as is the disconnect actuator).

I hooked up the old motor and everything works normally.

I hooked up the new one again and same problem flashes for 30 secs and goes dead.

I ohmed out the new motor connector and it seems okay / similar to the old one (~4 ohms on motor terminals, ~20 ohms on brake terminals and ~2000 ohms on encoder pot terminals).

I tried plugging it in just dangling (not installed on the transfer case) just in case the motor was too weak to move the transfer case clutch shaft and get same issue (selector light flashes for 30 secs and go dark, motor never tried to run).

I tried hot wiring it (i.e. energize both brake solenoid and motor) and the motor turns fine.

I'd really appreciate any ideas what could be wrong... Thanks!

[ErikSS]

Did you try with the actuator motor connected? I know there are more wires there than just hot and ground going to that location. 4 I believe. It seems possible that your computer is waiting for a return signal from the actuator before sending power to the encoder motor. They seem to go at the same time on mine, but I have custom wiring. I hope one of the electrical engineers we have come in soon!

[njohns]

Thanks for the thought. I agree it may work that way -- it seems like there's something it doesn't like right off the bat before trying to energize the motor.

But its just a single 7-terminal plug (2 motor, 2 brake, 3 for encoder pot). It tried plugging and unplugging to make sure I had a good connection.

I'm hoping its something simple as I'd like to get it done tonight before I have to give up and put the old one back on so I can drive it tomorrow. It snowed here today so I'm working in a puddle of melted snow under the truck. Seemed like it would be a quick and simple job but has turn into a real pain...

[Trail X]

Indeed, that is strange. It really sounds like a bad connection to me. I'd return the new motor for another one. Though, you said yourself that you could power the brake open and run the motor... so that, to me, means its gotta be a bad signal on the pot. Bill knows more about the internal operation of the tccm and motor though. I'll gladly defer to him.

[The Roadie]

I'm speculating the pot connection as well. Can you probe the endpoints and wiper signals while it's plugged in and running? I forget if the connector is probeable or if you have to use the pin through the insulation trick.

[njohns]

Thanks for the input guys.

A connection issue does seem to make the most sense although it is pretty hard to believe that a new plug would not be making contact on multiple tries when the old one does, but maybe my intermittent problems were a bad connection all along rather than the old motor itself.

I gave up late last night and put the old one back on while I was still wet and dirty now I'll wait for a dry, warmer day to fool with it again. Maybe I'll try to jump all seven connections with clip leads and see what happens.