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4x4 is not working.. Transfer case

EIB8400

EIB8400

1/2 ton status
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Location
Delaware, Ohio
I just got a 1999 2500 suburban from a member on here. I got a good deal and love the truck but, I have an issue. I knew the 4x4 was not working when I bought it. There is a light on the dash that says "service 4x4" and the push buttons on the dash for the 4x4 do not light up at all. I've checked all of the fuses and they are all good. I had a friend with a nice scanner scan it and it didn't pick anything up.

Anybody have any suggestions besides the obvious (fuses, loose connections)?

Is there any way to find out what the code is? Make the light flash or some kind of magical way to figure it out?:dunno:

Thanks for any help.
 
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Hey Eric,
If I remember correctly, the Matco scanner I plugged into it said code 'C308 A-B circuit volts low' . Hopefully someone can help and don't forget to update your siggy!
 
I forgot to change it. I've put a couple of hundred miles on it already and it runs great. It does take a little while for it to start sometimes. Might just need a tune up.
 
I change or repair a lot of the 4x4 push buttons. I will pull them out and take them apart and usually there is a broken solder on the circuit board. I will look up the code in a second and see if anything else is common.
 
Check the transfer case shift motor and the wiring.
If I remember right, there is an encoder in the motor that tells the module what position it is in, and if the signal not strong enough, it will set a code.

It might be a wiring problem, unplug and check all the connectors, or it may have gotten water into the shifter motor setup.
 
there is a bunch of other testing that i can post if necessary but most of it is testing for power to the automatic transfer case motor or powering it up from the wiring at the switch to see if it works. if the switch has a broken solder it can cause the same problem.
 
DTC C0308 MOTOR A/B CIRCUIT LOW (TRANSFER CASE - NVG 246-NP8 (TWO SPEED AUTOMATIC))
Circuit Description

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized, (through CKTS 1552, 1553, and the ground CKT 150 the module utilize for the motor control), the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between 4H, AUTO (Adapt), 2H, N, and 4L ranges.
This DTC detects a short to ground on CKT 1552 and 1553.
Conditions for Setting the DTC

​
• The system will test the motor circuits:
- The system checks for unwanted voltage.
- The system supplies voltage on one circuit and reads the voltage back on the other.
• If the system detects a problem with the circuits, the DTC is logged.
• The transfer case shift control module senses a low voltage return on CKT 1552 or 1553 when a high voltage is expected.​
Action Taken When the DTC Sets

​
• All shifting will be disabled.
• The SERVICE indicator (AWD/4WD) lamp will be latched on for the remainder of the current ignition cycle.​
Conditions for Clearing the MIL/DTC

​
• The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
• A history DTC will clear after 100 consecutive ignition cycles without a fault present.
• History DTCs can be cleared using a scan tool.​

376335.jpg
 
What is the easiest way to check for power at the transfer case motor? Is it supposed to have a constant 12v? The switch seems like it is not getting any power because none of the lights come on so I guess that is where I will start.

I will pull the switch out tomorrow and check it out.
 
So if I read that right it basically says that it is sensing a short in the transfer case motor? Or could it be something as simple as just a bad connection on the plug at the transfer case?
 
make sure you check the transfer case fuse and then check for power to the switch on the wire that provides it. if you have that then take the switch apart, they come apart easily and can be reassembled if no problems are found. then you will likely be into testing continuity of the wires from the encoder motor to the switch keeping an eye for corrosion at any of the plugs.
 
it also says if it senses low voltage it can code. possibly from an open wire or circuit on the circuit board. it is still possible to be wiring or the motor but you should test the stuff that is easiest to get at first.
 
You guys are awesome and fast. I will hopefully get sometime to check it tomorrow if not then on thursday. I will let you know what I find.

Thanks!
 
I am very glad you are happy with it and hope it is an easy fix! I wanted to post a before picture for all but you know how my computer skills are!
 
Okay... Everything at the switch looks okay even though it does not light up. I assume it does not light up because it is sensing a problem.
With the ignition on I am getting 5.04 volts at the transfer case motor. I was getting 5.04 volts on all but 1 (maybe 2) of the 6 pins at the plug. Should I be getting more voltage than that? Should most of the pins in the plug have the same voltage?
 
Here are some of the step by step test procedures. Read them all some of them overlap each other but they are mostly concerned with the wiring being able to carry current. If the pics aren't good enough i may have to e-mail them directly to you. Just check your powers and grounds and try to follow the tests.

1. Disconnect the module from behind the left side of the dash (behind the headlight switch).

2. Jump the Tan (1569) wire at terminal E1 of the Black connector to ground.

3. Jump the Orange (1640) wire at terminal D to the Red (1553) wire at terminal B.

4. Jump the Black (2150) wire at terminal C to the Black (1552) wire at terminal A.

5. Check for the transfer case to shift. Reverse polarity of the Red (1553) and the Black (1552) wires, and check for the transfer case motor to change directions.

6. If the transfer case does not shift, repeat the procedure using the same wire colors and the motor on the transfer case.

7. If the operation of the transfer case is normal, verify that the module is powered and grounded properly and replace if necessary.

Another...

1. Check the Red and Black wires running from the Transfer Case Control Module (TCCM) to the transfer case shift motor for shorting to ground.

2. Ohm from each pin of the motor to the case of the motor itself and make sure that there is no continuity.

3. If the wiring is OK and the motor is not shorted to its case, then replace the TCCM.

Yet another...

1. Remove the TCCM from under the Left Hand (LH) side of the Instrument Panel (IP), check for corrosion.

2. Replace the TCCM if corroded at the pins.

3. TCCM disconnected, check resistance of the transfer case shift motor, pin A Black to pin B Red.

4. Should have 0.5 to 35 ohms.

5. Check each wire for continuity to ground, should indicate open. NOTE: Wait 10 seconds prior to taking final ohm reading during this test to allow for capacitor charge.

6. Disconnect the transfer case shift motor.

7. Connect a head lamp from pin A Black to pin B Red.

8. Through fused jumper wires, supply B+ and B- to the same Black and Red wires, pins A and B at the TCCM, check that the head lamp lights bright.

9. Switch polarity, verify that the head lamp remains bright.

10. With the head lamp glowing, wiggle C131, check for change.



I can't think of anything else to help you without me climbing out of your tool box.

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More than likely its the encoder motor, a simple yet expensive fix.
Fairly common problem,I've replaced a lot of them.
 
Avery4jc - Mine has push buttons on the dash. I wish it wash the floor shift.

jake 03 - I'm guessing that the encoder motor is the motor on the transfer case?
 
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