Powertrain Malfunction/Reduced Power Wrench Light

[ArchetypeNinja]

I got my 2021 STX 4X4 back from the dealer the other day and they saw the code thrown on the DTC, they said it was a “4X4 Transfer Case Mechanical/ Switch Circuit Failure” and even mentioned that the code was being generated more than I noticed on the back end of the vehicle's computer even though it didn’t trigger the dash light. But refused to look into it more because the light wasn’t present when they looked and they can’t recreate it (even though they see the code in the computer trigger multiple times). No TSBs are out of this issue either.

This is the second time my truck has been into the dealership for this issue with them saying the first time it was “just a glitch because the newer trucks have advanced computers and shouldn’t happen again”. Something is going on but it doesn’t seem like they want to take care of the issue to fix it.

Has anyone else experienced this or know the fix? I’m beyond frustrated that the dealer sees the issue in the computer but won’t investigate it because the “light isn’t triggering or triggered”.

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[DukeCanBuildit]

Have a look at the “Similar Threads” section down below this thread. This same thing was posted by another member recently - dealer was stumped but techs on this forum were pointing to a relatively simple first place to start. A sensor if I recall correctly.

 

[airline tech]

What code did it show?
P1870 or P1871?

How often do you use the switch to transition between 2H -4H and 4L?
Does it ever show any indication of not wanting to shift between them? if you use it regularly?

So, I understand correctly, you had the wrench light (ON) but at the dealer it was (OFF)
and the only code was for the Transfer Case Switch (History Code)

It should be troubleshot with a detailed Live Data monitor test. Looking at Switch Position (PID)
Cycle the switch and see if the PID follows the switch position.

Switch is just power and ground, but switch position is communicated on the HS2- Can Bus with ABS Module as one of the many tied into the circuit (Looking at Wheel Speed Sensors)

 

[ArchetypeNinja]

What code did it show?
P1870 or P1871?

How often do you use the switch to transition between 2H -4H and 4L?
Does it ever show any indication of not wanting to shift between them? if you use it regularly?

So, I understand correctly, you had the wrench light (ON) but at the dealer it was (OFF)
and the only code was for the Transfer Case Switch (History Code)

It should be troubleshot with a detailed Live Data monitor test. Looking at Switch Position (PID)
Cycle the switch and see if the PID follows the switch position.

Switch is just power and ground, but switch position is communicated on the HS2- Can Bus with ABS Module as one of the many tied into the circuit (Looking at Wheel Speed Sensors)

The dealership actually didn’t tell me what code in the DTC was thrown other than the name of 4X4 Transfer Case Mechanical Switch Circuit failure.

I only use the switch during the winter months with snow when I can’t get traction, and is normally only is 4H and hardly ever in 4L if in 4WD.

That is correct both times it went into the dealership the Wrench light was no longer illuminated. Both times the light came on it was in 2WD just driving normally and no limp mode, the light turned off once I cycled the ignition switch. They also mentioned to me that other than the 2 lights I claimed to have seen triggered, that same code was thrown many more times (unknown on how much more).

 

[airline tech]

If the only code is P1870 - Mechanical Transfer Case 4X4 Switch Circuit Failure
and no other codes from ABS or Communication then it is possible that the switch is bad or a power ground loss to the switch.

Did the Switch have (Lighted) switch position when in failure mode? (2H) was it illuminated?

Being that this is intermittent, and the switch is easy access and not bad price wise, I would possibly just throw a switch at it.
But I would factor in - Has anything ever been spilled on the switch (Drinks) from the nearby cupholder?
If yes, then most likely the switch

It could just be a bad connection at the Switch Connector (C3393)
Did the fault generate when going over a bump in the road?

You can possibly isolate a wiring issue by disconnecting the connector and meter out Pin 1 and Pin 7. (Switch Connector)

Ignition On:

Use a test-probe small enough to fit in the connector without damaging the pins.
Pin 1: Brown / Yellow - Power
Pin 7: Black / Blue - Ground

Note: Pins 3 and 6 = Can Bus wires (Twisted Pair), these are the data comm wires for actual switch position, but an issue here should generate other fault codes, Communication and also other module codes triggered by that data loss.
Since the only reported code is switch failure, we can possibly eliminate this as an issue.

With the probes connected, shake the harness to verify that the wiring is good, must maintain battery voltage on the meter.

Pin 1 (Positive Test Lead)
Pin 7 (Negative Test Lead)

If you get fluctuation in voltage (with a valid and secure connection) at your test leads to connector.
Then you need to isolate is it losing power or ground

Then Probe Pin 1: Power and then the (Neg) lead to body ground, while shaking the harness does voltage still fluctuate.
If yes, then it's a power issue (not to far forward of the switch connector) is an inline connector (C311)
You will have to follow the switch connector forward to find it.

Note: If you get fluctuation when shake testing the harness (Pin 1 to Pin 7) and do not get voltage fluctuation when shake testing (Pin 1 to Body Ground) then you have a bad ground

C311 Connector:
Now: Probe Pin 8 on that connector and then (Neg) lead to body ground, shake test the harness, did the voltage hold constant.
If yes, then either a bad wire between C311 and C3393, or a dirty connection at C311 (Pin 8)
Pin 8 = Brown / Yellow wire

If No: Then (If no other fault codes are issues noted) then the issue is between the power splice and C311 and requires the harness to be opened up to that splice point.

If the wiring checks are good, then its highly likely it's the switch itself.

You may fix the issue just by disconnecting and reconnecting the connectors C3393 and C311

Note: The reason I am stopping at C311 is due to the fact that this is a shared power circuit, and is spliced off of that power circuit and the first connector from that splice is C311 feeding only the 4WD switch

 

[RedlandRanger]

I just have to say - @airline tech - your diagnosis skills are amazing - and without ever seeing the vehicle, too! You are a dying breed - not too many "technicians" these days are good at diagnosis - unless a code is thrown or the computer says "replace this part" they are lost.

We are blessed to have you as part of this community! Thank you for all you do to help our members!

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