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4wd Actuator

FRONT DRIVESHAFT (Propeller Shaft) SPEED SENSOR — Provides an AC signal to the ATCM, indicating the front driveshaft speed. The ATCM uses this signal to calculate the amount of rear axle slip during Auto 4WD mode.
This sensor is also used to determine the percentage of torque to be applied to the front differential during Auto 4WD mode.
REAR DRIVESHAFT (Propeller Shaft) SPEED SENSOR — Provides an AC signal to the ATCM indicating the rear driveshaft speed. The rear driveshaft speed sensor is used to calculate rear axle slip during AUTO 4WD mode.
VEHICLE SPEED SENSOR — Located on the transfer case output shaft, the PCM uses the vehicle speed sensor signal to determine vehicle speed. The PCM then shares this information with the ATCM via the Class 2 serial data lines.

So it sounds like the Vehicle Speed sensor impacts 4 Low, The front and the rear driveshaft speed sensors impacts AWD.
 
Husker6.5 said:
Do you have the two rear sensor plugs swapped around so that the wrong signal is being sent to the wrong control module, by chance?
Click to expand...
Mechanic did the install. Based on pictures, they appear to use the same plug, so it wouldn't hurt to swap. That said, it did work through summer with the indicator lights solid at the switch, which points more towards a failure during that timeframe.
 
Have you checked the wiring thoroughly?
Most likely culprit.

I would check with voltmeter for a grounded out power lead at harness connector.

I think I saw in another post you ordered a rebuild kit for this transfer case. Make sure you get the upgraded oil pump or a aftermarket guard piece to protect case from pump rub. These auto-trac cases are prone to pump rub working a hole into aluminum case. Causing fluid leak.
 
Bowhunterbrown said:
Have you checked the wiring thoroughly?
Most likely culprit.

I would check with voltmeter for a grounded out power lead at harness connector.

I think I saw in another post you ordered a rebuild kit for this transfer case. Make sure you get the upgraded oil pump or a aftermarket guard piece to protect case from pump rub. These auto-trac cases are prone to pump rub working a hole into aluminum case. Causing fluid leak.
Click to expand...
I did inspect the wiring today. It would be impossible to incorrectly install the plugs due to the lengths of the leads. It was apparent that there was a prior repair as there were crimps in place:
56DB5A20-1264-43D7-9588-9A9DCC7E2CD1.jpeg14D3357C-1BB3-4D82-910B-D5A26CC3C24C.jpeg
They were shrink fit crimps which had not been shrunk. I cut them out and installed new ones, but no difference.

Have not checked with voltmeter. Would I do this at the harness connector? If so, how?

Rebuild kit was for an NP 241-C case, which did not have the pump rub issue. Completely separate case, no pun intended. It’s a case from a ‘95 that’s going in a ‘94 where the existing case has a leak in the seal between the transmission.

This thread is on a purchased reman NP 246 with auto trac installed in March 2022. The rear case half is aluminum, not magnesium like OEM. They did all the pump rub corrections. Shop is legit and offers a 2 year, 70K mile warranty. Transfer case itself is not the issue.

I can clearly hear the encoder motor shifting when I press 4 High and AWD buttons, but the lights stay flashing on the switch. I hear nothing on 4 Low and light on switch stays flashing.
 
Last edited:
Big T said:
I did inspect the wiring today. It would be impossible to incorrectly install the plugs due to the lengths of the leads. It was apparent that there was a prior repair as there were crimps in place:
View attachment 79018View attachment 79019
They were shrink fit crimps which had not been shrunk. I cut them out and installed new ones, but no difference.

Have not checked with voltmeter. Would I do this at the harness connector? If so, how?

Rebuild kit was for an NP 241-C case, which did not have the pump rub issue. Completely separate case, no pun intended. It’s a case from a ‘95 that’s going in a ‘94 where the existing case has a leak in the seal between the transmission.

This thread is on a purchased reman NP 246 with auto trac installed in March 2022. The rear case half is aluminum, not magnesium like OEM. They did all the pump rub corrections. Shop is legit and offers a 2 year, 70K mile warranty. Transfer case itself is not the issue.

I can clearly hear the encoder motor shifting when I press 4 High and AWD buttons, but the lights stay flashing on the switch. I hear nothing on 4 Low and light on switch stays flashing.
Click to expand...
Are you moving?
Our 98 would never go in gear unless it moved. It didn't take much movement. But it had to move.
If you were stuck to the point of not moving, you stayed stuck.

I would start at the switch and figure out what's supposed to happen at the switch when you push low lock.

And check to see that power is going to where it's supposed to go.

Have to get a schematic and verify what the previous owner did with the splicing.

He may have changed something eliminating the low lock feature.

you might stumble on something checking the power from the switch
 
RI Chevy Silveradoman said:
I think Big T said it was working in the current wire configuration. Then it stopped working.
Click to expand...

Went out just now to test it while moving. 4 High the light flashes on the switch, but it is clearly in 4 High. Truck bucks on tight turns and when you press 2 High, it releases and drives smooth. Same for AWD, light flashes on switch, but AWD is working, though bucking does not show up on pavement. 4 Low light flashes on switch and it never goes into 4 Low. Eventually flashing light reverts to solid on 2 high button. I did this in neutral while slowly rolling. It's a signal thing and I need to get under there and do the voltage tests to the encoder motor, but I do know the encoder motor is working.

Amazon sent message of delayed shipment on the sensors, either 19th or 20th.
 
This guy has the best NP 246 repair video yet. Although I don't appear to have the exact same problem, the portion on the grounds is one to focus. In the end, he saves with an encoder motor pulled from a boneyard, so he's a spirit brother. Love his scan tool and I want.


Located in Avoca, NY in the heart of rusted out vehicles. Seems like we have one or two located there.
 
Husker6.5 said:
Data Link Malfunction would tend to point to a wiring/TCM issue, one would think. I wonder if @THEFERMANATOR or @Rockabillyrat have any words of wisdom on the subject?
Click to expand...
While I have that data link malfunction, I do get data on command positions.

In this pic I commanded 4Hi and it shows encoder position of 4Hi, but notice the 4Hi indicator light is flickering just as it does on the button in the cab.
1CC3FC51-6908-40D3-8B42-49BF50358A16.jpegA35FAAFC-B9C4-4CB5-B463-DCABFD571D16.jpeg356EA3F8-426F-4E19-B2B7-20EE57AC75E0.jpegC134ED27-88B9-4F46-B3CB-716A213121C8.jpeg7B290064-83C0-403F-B207-22BD358C6E81.jpeg8607CC6E-5CA5-4564-9A30-8CB49D0EE859.jpeg
 
But were you getting data on the transfer case, not just the switches? It looks like all data on those screens pertained to the switch positions.

Again, why when I bought my '98 LT K2500 6.5 Burb I made sure it had the mechanical transfer case with the lever on the floor, as even back in 2010 there were already the issues with the push button transfer cases you're having with yours.
 
Husker6.5 said:
But were you getting data on the transfer case, not just the switches? It looks like all data on those screens pertained to the switch positions.

Again, why when I bought my '98 LT K2500 6.5 Burb I made sure it had the mechanical transfer case with the lever on the floor, as even back in 2010 there were already the issues with the push button transfer cases you're having with yours.
Click to expand...
Seems there were issues since they were new.

At least , what I considered issues
 
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