Service 4X4 light goes on after a short drive

Tiny
JOEBUZZ
  • MEMBER
  • 1999 GMC SUBURBAN
  • 7.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 110,000 MILES
Just replaced dash drive switch. The horizontal button one. The vehicle listed above is a K2500 Suburban SLT 8600gvw. The ground location for the front differential and the transfer case shift motors are not on the frame under the driver side. For the front differential drive motor the wires head up a tube at the right rear of the engine and I have no idea where they end up. Haven't followed the transfer case motor wires yet. The front differential motor works, pulled it and verified. It does shift to 4x4 two wheel, 4x4 four wheel high, but not 4x4 low. It also gets stuck in 4x4 high but manages to get back to two wheel drive. Hubs have been overheated recently due to calipers seizing. 4x4 Service light came on at that time. Could a hub be causing the 4x4 Service light to come on?
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Tuesday, March 9th, 2021 AT 10:21 AM

12 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

I don't feel the hubs would cause the transfer case issue. I suspect it deals with the encoder motor. If you look at pic 1, I attached an exploded view of the transfer case and circled the encoder motor. The first thing I suggest is to inspect the plug for pushed in pins, corrosion, or any evidence of damage. That it checks good, here are directions for testing the encoder motor. Pic 2 correlates with the directions.

____________________________

1999 Chevy Truck K 2500 Suburban 4WD V8-454 7.4L VIN J SFI
Transfer Case Will Not Complete A Mode or Range Shift
Vehicle Transmission and Drivetrain Transfer Case Testing and Inspection Symptom Related Diagnostic Procedures NVG 243-NP1 (Two Speed Selectable) Diagnosis By Symptom Transfer Case Will Not Complete A Mode or Range Shift
TRANSFER CASE WILL NOT COMPLETE A MODE OR RANGE SHIFT
Transfer Case Will Not Complete A Mode or Range Shift

Circuit Description

This symptom indicates that the transfer case encoder motor circuits are not functioning properly. This symptom is similar to DTC 003 but differs because the counter inside the transfer case control module (TCCM) has not yet set DTC 003. One of the following conditions may exist.

- One of the internal power relays in the (TCCM) is not energizing or deenergizing.
- An open exists in the Battery Positive Voltage, Ground, Motor Control A or Motor Control B circuits.
- A short to ground exists in the Battery Positive Voltage, Motor Control A or Motor Control B circuits.
- A short exists within the motor or TCCM.

The transfer case encoder motor has a bi-directional permanent magnet, D.C. Motor. When a shift request is made by the TCCM voltage will be applied through one of the motor control circuits and the TCCM will provide the ground through the other motor control circuit. When a shift is requested in the opposite direction, the TCCM will reverse polarity on these two circuits. The motor through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between gears.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. This step tests the functionality of the transfer case shift control system.

Transfer Case Will Not Complete a Mode or Range Shift

pic 2

______________________________

Let me know what you find or if you have other questions.

Take care,
Joe
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Wednesday, March 10th, 2021 AT 6:00 PM
Tiny
JOEBUZZ
  • MEMBER
Thank you for your rapid response. I tried to find where my grounds were since they're not on the frame under the driver door. The 99's seem to be a different animal in some respects. I cleaned and dielectric greased the plugs at both actuator motors, drove 5 miles, Service 4x4 light came back on. I'm afraid to try to put it into 4x Low because of the trouble I had getting back to 2 wheel before I installed the new dash switch. Is there someplace you know that the ground could be other than the frame? I'm presently ordering a new shift motor for the front differential just because it didn't run smoothly and had to be "switched" 3 or 4 times to make it work every time.
Due to your response I tried to find information on DTC 003 trouble shooting and couldn't find anything on the internet related to that code. My OBD II reader is an inexpensive model that shows no fault codes. Works with my android phone. One article I read noted that there will be no code associated directly with the transfer case shift motor. Is there a way to verify that the plug at the transfer case shift motor is actually getting volts? I'm not big on electrical.
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Friday, March 12th, 2021 AT 1:03 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Just for curiosity, is the brake light stay on or the ABS light?

Joe
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Saturday, March 13th, 2021 AT 7:26 PM
Tiny
JOEBUZZ
  • MEMBER
Hi, thanks for your reply.
No, just the "Service 4x4" light. Here's the strange part: I start out cold, drive 1 or 2 miles the light comes on, stays on until I shut off the engine for a while. When I drive it again, it goes 1 or 2 miles and comes on. I put dielectric grease on it the other day. It went about 6 miles before the light came on. The next day, about 10 miles. Today I will take all the plugs I greased and clean and plug them in a few times. If the light stays off I'll try 4x Low. I've been very afraid of it getting stuck in 4x. It did a couple weeks ago and I thought it would be stuck there until I figured it out. It's my only vehicle. I may take the intake stuff off today, open the wire loom and try to figure out where the ground actually goes.
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Sunday, March 14th, 2021 AT 7:16 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Let me know what you find or if you have other questions.

Take care,
Joe
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Sunday, March 14th, 2021 AT 6:50 PM
Tiny
JOEBUZZ
  • MEMBER
Hi,

Thank you for the reply. What I found was that the overheating of the right side rotor melted the wire insulation to the hub. Wire is exposed but I can't tell which wire since I can't see into the space between the rotor backing plate and the spindle/knuckle. So whatever those wires can cause "may" be the problem. I need ball joints so I guess I have a lot of work to do. The plugs all seem in good shape at the transfer case and differential motors. I'll not use the 4x until I've done it all. Thank you for your assistance.
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Monday, March 15th, 2021 AT 9:57 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Is it the wiring to the wheel speed sensor?

Let me know.
Joe
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Monday, March 15th, 2021 AT 11:34 AM
Tiny
JOEBUZZ
  • MEMBER
Hi Guys,

Yes, I believe it is. I'm looking at new hubs now. One repair guy say's "speed sensor" wires, another say's "anti lock" wires. However, it's two wires in one insulation (now melted), a black and a white. If it's a speed sensor, okay. If it's an anti lock wire? Couldn't tell you what it actually does. It's the only electrical connection to the back of the hub.
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Monday, March 15th, 2021 AT 11:59 AM
Tiny
JOEBUZZ
  • MEMBER
Hi.
I attached a possible part. Note that in the same ad one line says "speed sensor" and then below it says "ABS" ---- sensor. So honestly, to me it's confusing. Speed sensor, ABS sensor, hey, I'm not sure now what to call it.
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Monday, March 15th, 2021 AT 12:17 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

It's an ABS sensor. The one in the pic shows the entire hub assembly with the sensor. You could just replace the sensor.

Here are the directions. The attached pics correlate with the directions.

_______________________________________________

1999 Chevy Truck K 2500 Suburban 4WD V8-454 7.4L VIN J SFI
Wheel Speed Sensor Replacement
Vehicle Sensors and Switches Sensors and Switches - Brakes and Traction Control Wheel Speed Sensor Service and Repair Procedures Wheel Speed Sensor Replacement
WHEEL SPEED SENSOR REPLACEMENT
REMOVAL PROCEDURE

pic 1

1. Raise vehicle.
2. Remove tire and wheel.
3. Remove brake caliper.
4. Remove the hub and rotor.
5. Remove wheel speed sensor mounting clip (2) on the control arm.

Pic 2

6. Remove wheel speed sensor mounting clip (2) on the frame rail.

Pic 3

7. Remove wheel speed sensor electrical connector (6).

NOTICE: Carefully remove the sensor by pulling it straight out of the bore. DO NOT use a screwdriver, or other device to pry the sensor out of the bore. Prying will cause the sensor body to break off in the bore.

IMPORTANT: The wheel speed sensor mounts into a bore that leads to the center of the sealed bearing. Use caution when cleaning or working around the bore. Do not contaminate the lubricant inside the sealed bearing. Failure to do so can lead to premature bearing failure.

8. Remove wheel speed sensor from hub and bearing assembly.

INSTALLATION PROCEDURE

pic 4

IMPORTANT: The new speed sensor will have a new O-ring. Dispose of the old O-ring. Lubricate the new O-ring lightly with bearing grease prior to installation. You may also lubricate the sensor just above and below the new O-ring. Do Not lubricate the bore.

1. Install sensor into the hub and bearing assembly (5).
Tighten the sensor mounting bolts to 18 Nm (13 ft. Lbs.).

IMPORTANT: The new sensor has new mounting clips already installed on the wire. Do not reuse the old clips.

Pic 5

2. Install wheel speed sensor electrical connector (6).

Pic 6

3. Install wheel speed sensor mounting clip (2) to the frame rail.

Pic 7

4. Install the wheel speed sensor mounting clip (2) to the control arm.
5. Install the hub and rotor.
6. Install brake caliper.
7. Install tire and wheel.

________________________________________-

I hope this helps.

Take care,
Joe
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Monday, March 15th, 2021 AT 5:48 PM
Tiny
JOEBUZZ
  • MEMBER
Hi Joe,

Thanks again for your assistance. I've ordered "everything" for an entire front end rebuild accept brake parts as they were all new in November. After I get the hubs on and before I try to do anything else I'll let you know if the hub wires melting was the cause of the "Service 4x4" dash light. It'll be a couple weeks. Waiting on parts shipments now. I'm 67 and my mechanic-ing ain't as quick as it used to be.

Best Regards,
Tom
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Sunday, March 21st, 2021 AT 4:59 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi Tom.

No problem. Take your time. When you have the chance, let me know. I'm not too far behind you and know exactly what you mean. LOL

Take care,
Joe
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Sunday, March 21st, 2021 AT 6:10 PM

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