10 replies to this topic

[eheath]

Can anyone tell me if there are any common problems causing the service 4wd light to come on. The truck is push button and the 4wd engages and works. Thanks e

[MS3DALE]

Most common issue is the dash switch.

[eheath]

Thanks, i'll try ebay or LMC. e

[MS3DALE]

Not saying for sure thats your issue,but thats the cheapest thing to try first,and we sell quite a few of them at the dealership for that issue.

[eheath]

Thanks, i'll try ebay or LMC. e


Would a code reader pick up the problem. I saw one on the program truck-u. I think it was universal and not too expensive.

[MS3DALE]

A code reader/scan tool "might" help you determine the issue,if its setting a code.

Heres one example...

DTC B0790
Circuit Description
The Neutral indicator circuit consists of an ignition 3 voltage circuit and a Neutral indicator control circuit. When the Neutral mode has been selected by the driver, current is supplied to the Neutral indicator by the ignition 3 voltage circuit, traveling through the Neutral indicator LED at which time the transfer case shift control module supplies the ground through the Neutral indicator control circuit. This DTC detects an open, short to ground, or a short to voltage.

DTC Descriptor
This diagnostic procedure supports the following DTC:

DTC B0790 Transfer Case Neutral Indicator Circuit Malfunction

Conditions for Running the DTC
• The ignition is ON.

• The system voltage is 9-18 volts.

Conditions for Setting the DTC
• The system monitors the voltage on the Neutral indicator control circuit.

• If the system detects a voltage of 3 volts or less for 1.5 seconds when the Neutral indicator is not commanded, the DTC is logged.

• If the system detects a voltage of 4.5 volts or more when the Neutral indicator is commanded, the DTC is logged.

Action Taken When the DTC Sets
The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
• The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.

• A history DTC will clear after 100 consecutive ignition cycles without a fault present.

• History DTCs can be cleared using a scan tool.

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

This step inspects for the visual operation of the Neutral indicator Light. Command both the ON and OFF states.

This step tests for voltage at the Neutral indicator feed side of the transfer case select switch.

This step verifies that the transfer case shift control module is providing ground to the Neutral indicator.

This step tests if ground is constantly being applied to the Neutral indicator.

This step tests the control circuit of the Neutral indicator for a short to voltage or an open.

This step tests the control circuit of the Neutral indicator for a short to ground.

Step
Action
Yes
No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1
Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to Diagnostic System Check - Vehicle

2
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, command the Neutral Indicator Light ON and OFF.
Does the Neutral Indicator Light turn ON and OFF with each command?
Go to Testing for Intermittent Conditions and Poor Connections
Go to Step 3

3
Turn the ignition OFF.
Remove the transfer case select switch.
Disconnect the connector on the transfer case select switch.
Turn the ignition ON.
Probe the ignition 3 voltage circuit with a DMM that is connected to a good ground.
Does the DMM indicate battery voltage?
Go to Step 4
Go to Step 10

4
Connect a DMM between the harness connector of the neutral indicator control circuit and the ignition 3 voltage circuit.
With the scan tool, command the Neutral indicator ON and OFF.
Does the DMM indicate battery voltage and then 0 volts with each command?
Go to Step 8
Go to Step 5

5
Does the DMM continue to indicate battery voltage with each command?
Go to Step 7
Go to Step 6

6
Test the neutral indicator control circuit for a short to voltage or an open. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?
Go to Step 13
Go to Step 9

7
Test the control circuit of the neutral indicator for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?
Go to Step 13
Go to Step 9

8
Inspect for poor connections at the transfer case shift control switch. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs .

Did you find and correct the condition?
Go to Step 13
Go to Step 11

9
Inspect for poor connections at the harness connector of the transfer case shift control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?
Go to Step 13
Go to Step 12

10
Repair the ignition 3 voltage circuit of the transfer case select switch for an open, a high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?
Go to Step 13
--

11
Replace the transfer case select switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?
Go to Step 13
--

12
Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the repair?
Go to Step 13
--

13
Use the scan tool in order to clear the DTCs.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC set?
Go to Step 2
System OK

[eheath]

I really appreciate all your input and knowledge. Thank you. e

[oubobcat]

I have a 2004 and Get the Service 4wd message on the DIC occasionally, as recent as 1 wk ago.

My Scan Guage tells me no trouble codes have been set.

Since I get the Service 4wd Message with no codes does that mean it is the switch? I'm looking to order one from GM parts direct.

[My06GMCSierraZ71]

Can anyone tell me if there are any common problems causing the service 4wd light to come on. The truck is push button and the 4wd engages and works. Thanks e

I have seen many posts for the Service 4WD issue and the fact that hundreds of people have the same problem as me. I have a 2006 Sierra Z71 and have had problems with the 4WD for some time now. My truck would go into 4WD on its own and then wouldn't go into 4WD when I wanted it to. The light would say one thing, my front end grinding around corners and poor fuel mileage said another. I took it to the dealership, they charged me $100 to tell me what was wrong. It was the Encoder Motor on the transfer case and the Transfer Case Control Module. They wanted $1600 to fix it. BUT... I have some good news for people with the same problem!! The Transfer Case Control Module is located under the driver side dash, just above the E brake. You DO NOT need to take apart the dash, at least on the 06 model. I changed the TCCM in about 10 minutes in a freezing cold parking lot. The Encoder Motor I bought a new rebuilt off Ebay from BuyAutoParts.com for $250 and that included shipping. The company was great to work with as well. It was VERY easy to change with basic hand tools. I had it swapped out in 30 minutes, start to finish and was driving it 5 minutes later. I know my way around trucks a little, but I am far from a "mechanic". My 4WD works like a champ now. Take it from me, don't pay thousands for labor because it wasn't hard at all. I am posting this on several different boards because when I needed help, I couldn't get any straight answers. I hope this helps someone out there and Good Luck

[sabre364]

Thanks. Folks like you really make our communities worth it. I have a friend with an 01? tahoe that has 130000 and has the same issue. Figured it was the dash switch but if that didn't work he's gonna have to go to theh more expensive parts.

Can anyone tell me if there are any common problems causing the service 4wd light to come on. The truck is push button and the 4wd engages and works. Thanks e

I have seen many posts for the Service 4WD issue and the fact that hundreds of people have the same problem as me. I have a 2006 Sierra Z71 and have had problems with the 4WD for some time now. My truck would go into 4WD on its own and then wouldn't go into 4WD when I wanted it to. The light would say one thing, my front end grinding around corners and poor fuel mileage said another. I took it to the dealership, they charged me $100 to tell me what was wrong. It was the Encoder Motor on the transfer case and the Transfer Case Control Module. They wanted $1600 to fix it. BUT... I have some good news for people with the same problem!! The Transfer Case Control Module is located under the driver side dash, just above the E brake. You DO NOT need to take apart the dash, at least on the 06 model. I changed the TCCM in about 10 minutes in a freezing cold parking lot. The Encoder Motor I bought a new rebuilt off Ebay from BuyAutoParts.com for $250 and that included shipping. The company was great to work with as well. It was VERY easy to change with basic hand tools. I had it swapped out in 30 minutes, start to finish and was driving it 5 minutes later. I know my way around trucks a little, but I am far from a "mechanic". My 4WD works like a champ now. Take it from me, don't pay thousands for labor because it wasn't hard at all. I am posting this on several different boards because when I needed help, I couldn't get any straight answers. I hope this helps someone out there and Good Luck

[3beejay3]

Th

I have seen many posts for the Service 4WD issue and the fact that hundreds of people have the same problem as me. I have a 2006 Sierra Z71 and have had problems with the 4WD for some time now. My truck would go into 4WD on its own and then wouldn't go into 4WD when I wanted it to. The light would say one thing, my front end grinding around corners and poor fuel mileage said another. I took it to the dealership, they charged me $100 to tell me what was wrong. It was the Encoder Motor on the transfer case and the Transfer Case Control Module. They wanted $1600 to fix it. BUT... I have some good news for people with the same problem!! The Transfer Case Control Module is located under the driver side dash, just above the E brake. You DO NOT need to take apart the dash, at least on the 06 model. I changed the TCCM in about 10 minutes in a freezing cold parking lot. The Encoder Motor I bought a new rebuilt off Ebay from BuyAutoParts.com for $250 and that included shipping. The company was great to work with as well. It was VERY easy to change with basic hand tools. I had it swapped out in 30 minutes, start to finish and was driving it 5 minutes later. I know my way around trucks a little, but I am far from a "mechanic". My 4WD works like a champ now. Take it from me, don't pay thousands for labor because it wasn't hard at all. I am posting this on several different boards because when I needed help, I couldn't get any straight answers. I hope this helps someone out there and Good Luck

Does anyone have the part #'s for these? I have the same truck with similar problems.
A local mech. said that the encoder motor gets corroded inside and seizes up, causing the 4wd to stop working properly.

Thanks in advance.

BJ