Transfer case help….M1078 2001

[Xengineguy]

Ok, MY 4WD problem is solved. It was my VIM delete. A friend of mine shared some info about an issue he heard of where the 4WD failure turned out to be a bad 161-163 circuit. This pointed me back toward the VIM as that circuit does go thru the VIM. I misidentified that circuit when I did my VIM delete research as something to do with the PTO, and disregarded it as I don’t have a PTO, and it didn’t come up again in the WTEC 3 wiring which I was mimicking. On the A0 with WTEC2, they did 4WD like they did PTO. You send a PTO request signal to the TCU, the TCU in turn closes an output relay to send power to the PTO solenoid if it is happy with the current state of operation.

On the A0 WTEC2, you send a request to the TCU for 4WD/Mode Using the mode button. This changes the gear listing and The TCU in turn closes a relay via wire 114, which sends transmission signal ground(wire 161) to the retarder enable input 163. We use the retarder solenoid circuit H to control the center differential… Clipped a relay into that circuit, selected mode and the relay energized enabling the center diff using sig ground(161) to retarder enable 163…

i am going to do a little more research on how I will re-implement this, either add a relay to the panel or add a latching switch to control 4WD…

@Xengineguy Now that mine is working I will hook up my test connection again and document what the signal going to the C7 solenoid actually consists of in mode, and post that information here…

That would be great! I had mine in the shop today again. Checked the c7 coil and it seems to be very low impedance also. Checked
voltage to the coil was a little over 26v idle in mode. Checked the top of the coil with a feeler gauge for magnetism, none.
I didn’t have my scope at home but I can’t believe it’s 24v straight voltage . The coil would last about a second.
Mine also Set a code with just the c7 coil disconnected. Mine is a 2001 a1

 

[Ronmar]

@Xengineguy
Ok, i got a chance to take some readings. I don't have a 3 Ohm injector or solenoid to measure into so these were taken into a 85 Ohm 12v relay coil. Readings taken with a Fluke 87.

My A0 WTEC2 TCU won’t enable diff lock until the engine is running.

with the ignition on I get 61 milivolts @7.3Khz ~20% duty cycle. This is such a low input, there is basically no DC component. I believe this is the supervisory signal.
when I select mode the voltage jumps up to around 15V AC over about 3/4 of a second then settles at ~11VAC @ 7.3KHZ ~20% duty cycle.
During that first 3/4 second the duty cycle ramped up from 20% to over 50% then back to 20%, which looks like a peak and hold profile to me…