corey_lax

Hi Guys,

I have an issue that isn't your typical 4x4 related issue. My transfer case won't engage into 4x4. I have replaced the transfer case motor and it still won't shift into 4hi or 4lo. I have confirmed that there is power at the switch in the dash so no issue there. I have tried hot wiring the switch to confirm that the switch itself is not broken and that didn't change anything. All fuses and relays have been replaced, checked, and inspected.

I have had a PCM Read Only Error (P0605) recently. I had the dealership reflash the PCM a week ago and that code has not shown its ugly head yet. However, I believe the PCM error could be related to my transfer case issue (the PCM is not sending a signal from the switch to the transfer case). The engine light will come on eventually if this is the case but for now it remains off. Does anyone know if I can find a used PCM, and plug it in to verify if the problem is within the PCM? Or would I need to have the dealer program the replacement PCM, prior to installing it on my truck to "test" it?

corey_lax

Does anyone know if the wiring from the 4x4 dash switch, goes to the PCM prior to going to the transfer case?

techrep

iTrader: (1)

Is there a shift motor solenoid ?

corey_lax

Not really. The new shift motor comes as one unit. Solenoid connected to the motor basically. Just a few bolts and connect it.

Do do you know if I can pick up a used pcm from a similar truck with 4x4 and plug it in to see if it works? Or would the dealer need to program it for my truck to test it properly.

Im running out of ideas. I think it's going to have to go to the dealer for diagnosis.

greasyknuckles

I don't think the pcm gives the shift signal on these. I think it goes this way,
switch-gem module-relays-motor. pcm gets speed signal from the abs module
as does the gem. you said you changed the relay and motor and tested the switch.
that leave the gem and wiring. without a wiring schematic it will be tough to
test the wiring.

corey_lax

From what I can tell, our trucks don't have a GEM module like the previous model had.

corey_lax

My next thought is, could this be a problem with the dash cluster? Similar to how the power windows all run through the dash cluster.

About 6 months ago I had issues with my E-brake dash light staying on, and also my map lights intermittently turning on. I fixed this by removing the dash cluster and re-soldering all the connections. Perhaps I didn't do the 4x4 any favors and unsoldered an important connection by accident? Just a shot in the dark I guess, I don't know if the wiring goes into the dash prior to heading to the shift motor.

greasyknuckles

you are correct, forgot I wasn't in the '97-'03 forum. pcm has the 4x4 module built
into it. I don't think a 4x4 issue would cause the engine light to come on. without looking
at the manual and the tests for that code it is hard to say. I will say this, switch-pcm/4x4module-relays-shift motor. high current for the motor is routed thru the
relays with the pcm turning them on or off. pull a relay and with the key on using
a test light you should have a powered terminal, move testlight to power on the
battery and you should have a ground terminal (you may show 2 as the motor
may have a feedback thru the windings. then with a helper test the smaller
terminal to the relay while having helper switch it into 4x, testlight back to - on
batt. you should have a signal or power that energizes the relay to power up
the motor. if no signal than problem is either between the switch and pcm or between pcm and relay. again without being able to look at wire colors etc. it
will be tough

techrep

iTrader: (1)

You did find the 4WD fuses under the hood correct ?

corey_lax

Thanks for that. i will continue testing.

Yes, the fuses/relays under the hood have been checked.