I have been having trouble going from 4WD Hi directly to 2WD Hi for a few weeks. If directly selected, the 2WDHi button would flash for a while and then would go back to 4WDHI by itself. When this first happened, the service 4WD light would come on for a short time, but then that went out and did not come back on. By trial and error I found that if I first selected Auto mode, it would apparently go from 4WDHI to there just fine (the auto button would stay lit and the auto 4WD feature would stat working). Then if I selected 2WDHi from Auto mode, it would then complete and 2WDHI would stay lit. Never a problem going directly from 2WDHi to 4WDHi - only a problem going from 4WDHI directly to 2WDHi. All modes appeared to operate as designed once they were in and the light was on.

Last night the service 4WD light came on, the lights in the controls went out, and the vehicle was stuck in apparently 2WDHi.

Today I looked and found the ATC fuse was blown. I replaced it and cleaned/inspected terminals on the Shift Control Module (there was a small amount of corrosion on the Orange D pin terminal of C2. Now I have the indicator lights back in the 4WD control, but will not go to 4WDHi and I get straight 2WD operation in both 2WDHi and Auto.

I would like to test the encoder motor at C2 pins A and B, but don't know what resistance it should be (and if resistance if really a good test for it). I strongly suspect the encoder motor was drawing too much current and that is what blew the fuse.

I would also like to test the Shift Control Module side of the A and J pins of C108 to test the function of the shift control module. As I understand it there should be a pulse width regulated signal across these two pins when different modes are selected. Can anyone elaborate on what I should observe there?

Captain...... help!!!!

Thanks in advance,

Les

 

Les, just found this thread, sorry for the delay. The red & black wires at the encoder motor come from the TCCM connector C2 pins A & B. Resistance should be close to zero. Resistance alone will not tell the whole story. If either one of the wires shorts to ground, it will not show up. You'd need to check either wire for a short to chassis ground.


The ATC fuse feeds the motor circuit through the orange wire. Two constant grounds are supplied to the TCCM. The motor ground is at C2 pin C, and is under the dash, near the TCCM. Both the red and black wires at the encoder motor default to negative. To operate the encoder, ground is removed from one of the wires and positive is applied to it. The encoder motor is a DC motor so reversing the polarity changes the direction the motor operates. You can check amperage draw of the motor by connecting a DVOM inline in either of the wires and then operate the motor.

 

Hey thanks! Interesting but frustrating system. Guess I would really prefer a mechanical lever to push, but I'm afraid those days are gone forever and it will never be that easy again. This really reminds me of the heater temperature senders/programmers replacing a simple lever that operated the heat door through a mechanical cable. Does same thing but in a lot more complicated and trouble-prone way.

So it seems I could disconnect the TCCM and activate the encoder motor unlock by grounding the appropriate TCCM C1 pin. Then operate the encoder motor by applying voltage across C2 pins A and B while monitoring the current. Would the encoder motor shut off at its extreme positions - or would it just go to one end and the current go sky high? What if the encoder motor unlock was not working? Could that cause excessive current and a blown fuse if the TCCM commanded a failed unlock and the encoder motor tried to move?

 

There is no "shut off" switch in the encoder. The position sensor in the encoder is what "tells" the TCCM to remove voltage. If you operate the encoder from the TCCM connector, you are bypassing the sensor and the fuse. If you keep voltage and ground applied when it fully stops, current draw will increase which can burn up the wires, the encoder motor, or both. If the brake is locked, you could end up with the same result.


Also, with everything connected, if the brake is locked, or doesn't release, it will blow the fuse when the motor is activated.


The encoder on the NV233 transfer case has a position sensor, but there is no need for a brake.

 

To me it's sounding more and more like it has to be the encoder motor or the encoder motor lock causing the fuse to blow. It did it again.

Guess I'll check out the encoder motor and encoder lock wiring for opens or shorts to ground, and then go ahead with an encoder motor if nothing is found. Don't see what else could cause over 20A draw unless a direct short in the TCCM.

Let me ask you this.... Is there any reason why an uninstalled new encoder motor wouldn't be observed to move to different positions, if it is plugged into the harness and grounded (all other things being good)?

 

Do not activate the new encoder without it being installed on the transfer case. It will be destroyed, don't do it!


I'm 99% sure the transfer case must be in neutral when installing the new encoder. Instructions explain it. The encoder comes with an aligning jig installed on it. After you remove the old encoder, use a crescent wrench to manually shift the transfer case into neutral. You can feel the detents when you move the shift shaft. During installation, do not turn the encoder to line it up with the mounting bolts, it will damage the encoder. It should slide on the shift shaft and the bolt holes should align. After installation, the DTC's must be cleared in the TCCM before attempting to shift it with the dash switch. Being in neutral, you need to have a scan tool, or a tow truck to get it to someone with a scan tool that can access the TCCM.

 

Hey, Captain - thanks a bunch for the heads up! Looks like I really need to get out the shop manual again. Never even looked at the encoder replacement procedure yet. Kind of made a fool of myself with those questions.

But won't the procedure I posted in the other 4WD thread the other day work for clearing the codes? Aren't these the codes where there are 4 of them for the TCCM? 60 sec with the courtesy fuse out - then cycle key on/off 5 times to clear the code that gets set during the power down period? Please take a look and let me know. Was also instructions there for displaying the TCCM codes without a scan tool. Please advise your opinion.

Thanks,

Les

 

The NV236 requires a scan tool to retrieve the DTC's. They are 5 characters in length starting with "C" and they remain in memory until manually cleared with a scan tool. Disconnecting the battery will turn the service 4WD light off, and it will remain off provided there are no faults detected. This link explains: http://www.dormanproducts.com/digita...00-901_DTC.PDF

The NV233 codes, (not DTC's) are retrieved by jumping the pins and reading the flashes. If you pull the fuse to the TCCM on the NV233, the codes are lost until the next failure is detected.

 

Ok got it. Procedure I found was for a different transfer case. Thanks a bunch! Great info! Sometimes I feel like I know just enough to be dangerous!

 

On the NV236: If you don't clear the codes with a scanner after replacing the encoder, it will not shift correctly. Depending on the DTC, it might not shift at all, and you're stuck in neutral!