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Will not go into 4 low

Tiny
DEANVILLEBOBCAT
  • MEMBER
  • 2011 RAM 1500
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 162,000 MILES
My truck will not go into 4 Low, 4 Auto and 4 Lock work, when I shift into neutral and select 4 Low, the front axle locker actuates, I feel some movement I think in the transfer case actuator, but the light sequence goes to traction control off and then 4wd low flashes momentarily and then SRVC 4WD comes on. After reselecting 2WD on the 4 position switch and turning the vehicle completely off and restarting it the SRVC 4WD light is cleared out and I can use 4WD Auto or Lock again but still not Low.
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Tuesday, June 4th, 2019 AT 2:53 PM

21 Replies

Tiny
STEVE W.
  • MECHANIC
  • 12,958 POSTS
Welcome to 2CarPros. That sounds like an issue with the transfer case encoder position sensor. It's the switch on the encoder motor that tells the PCM what the encoder motor is doing. When you select 4 low the PCM isn't seeing the signal back telling it that the transfer case is fully engaged in 4 low so it errors out. It's an easy part to change but not cheap.
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Wednesday, June 5th, 2019 AT 5:26 PM
Tiny
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Thanks Steve. My local general mechanic shop read the code a couple months back now, it steered us toward a DTCM or flashing. Are any of those likely suspects? I don't want the Stealership to just start throwing parts at it and I would like to be as knowledgeable about it before hand.
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Wednesday, June 5th, 2019 AT 5:55 PM
Tiny
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Is this the part that is needed (servo and encoder integrated) or is it something else?
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Wednesday, June 5th, 2019 AT 7:23 PM
Tiny
STEVE W.
  • MECHANIC
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Well looking at the book and build information your truck can have two different encoder motors. One has the integrated sensor and the other is the bolt on sensor. I would verify which one you have. The connector looks to be the same on both so they might be interchangeable. The pinouts and wiring are in the pictures below. Testing with a voltmeter should tell you if the motor or the sensor is the problem. The only wire you really need to check is the mode sensor signal. It should show a different resistance for each mode the case shifts into. I suspect it will show nothing when shifted into low.
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Thursday, June 6th, 2019 AT 12:44 PM
Tiny
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How do I test this harness connector for resistance? Can you elaborate for me? My transfer case photo is attached.
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Saturday, June 8th, 2019 AT 8:51 AM
Tiny
STEVE W.
  • MECHANIC
  • 12,958 POSTS
The easiest way would be to use a needle to backprobe the yellow wire with the light green stripe in the connector circled. You would then watch the voltage change as you shift the truck into and out of 4low. If the voltage doesn't change or it stops you know there is a problem.

https://www.youtube.com/watch?v=Spy8AXlxVT0 Shows the back probe method.
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Saturday, June 8th, 2019 AT 3:43 PM
Tiny
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The voltage changed from 4 volts to 4 volts when shifted from 4auto to 4lock, then 4 volts to 5 volts when shifted from 4lock to 4 low. I felt the transfer case selection motor move but then the service 4wd light came on. I stuck my lead into the back of the connection of the green and yellow wire. I had my meter on volts dc and I had my other lead on the frame. When I disconnected the harness the service 4wd light came on. I’m not confident I checked the voltage correctly. What should it be?
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Saturday, June 15th, 2019 AT 7:39 AM
Tiny
STEVE W.
  • MECHANIC
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Check between the brown wire and a good ground. There should be 5 volts. From your description it sounds like there is a problem in the switch.
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Saturday, June 15th, 2019 AT 10:44 AM
Tiny
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Do I check this with the selector switch in 2WD?
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Monday, June 24th, 2019 AT 7:24 PM
Tiny
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Okay, so I have pinned the wire. I did yellow/green. It shows a spike to 1.9 volts then goes down and the srvc4wd comes on in 4low.

I pinned the brown wire and when switched to 4low, it jumps to 1.9 volts or so and then goes down. The srvc4wd comes on.
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Monday, June 24th, 2019 AT 7:59 PM
Tiny
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Is it 5 volts all of the time? When the truck is on or off? Switch in 2WD?
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Monday, June 24th, 2019 AT 7:59 PM
Tiny
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Now it’s really frustrating. I re-pinned the yellow/green and it’s reading 3.5v and it does so through all selections, until 4wdlow where it blinks and comes back up and then the srvc4wd light comes on.

I re-pinned the brown wire, it reads 2.5 all of the way through the selections until going to 4wdlow, then it blinks, and the srvc4wd light comes on. Please let me know what the next step is. Thanks! Yes
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Monday, June 24th, 2019 AT 8:13 PM
Tiny
STEVE W.
  • MECHANIC
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Sounds like the selector switch is bad. However you also are showing a low voltage to the switch. I would check the ground side of the system to be sure it isn't corroded anywhere.
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Monday, June 24th, 2019 AT 8:48 PM
Tiny
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I’m totally ignorant on the ground check. How do I do that?

As far as the selector switch, is that the switch in the cab?
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Monday, June 24th, 2019 AT 9:30 PM
Tiny
STEVE W.
  • MECHANIC
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The ground check is simply checking things like the body and chassis grounds from the battery. They corrode and you get lower voltages in various circuits. The switch on the encoder motor itself.
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Tuesday, June 25th, 2019 AT 1:12 AM
Tiny
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Where is the switch on the encoder motor located at? Is that the part where the encoder motor head bolts onto the transfer case?
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Tuesday, June 25th, 2019 AT 6:35 AM
Tiny
STEVE W.
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The switch is inside the top of the encoder motor.
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Tuesday, June 25th, 2019 AT 5:23 PM
Tiny
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Is it replaceable by itself?
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Tuesday, June 25th, 2019 AT 7:06 PM
Tiny
STEVE W.
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It depends on which encoder you have. The one you pictured earlier has an integrated switch. The newer ones have a replaceable unit.
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Wednesday, June 26th, 2019 AT 1:38 AM
Tiny
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  • MEMBER
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Thanks! How do I verify proper fitment for my truck? It looks like it is an ordeal based on what I’ve read on El Google. Is there a way to cross reference my VIN?
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Wednesday, June 26th, 2019 AT 3:39 AM

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