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Four Wheel Drive Service light

Our 2007 Chevy Tahoe 4 X 4 recently displayed a “Service Four Wheel Drive” panel light a couple of days ago (upon ignition on a sunny, dry day). The light had been steady which, when we read the owners manual, indicates a problem but no immediate service required. One of the possible solutions was to remove and close the gas cap in case it had been incorrectly closed during the last gas-up. That did not work. Yesterday, during a snow storm, I tried using the 4WD. The dial would move to the different settings, but no 4WD activated and no light illuminated indicating which gear it was in (2WD, Auto, 4H, 4L). We checked the fuse for the 4WD but it is OK.

I’d Bet That You Need To " Service Four Wheel Drive " .

" The light had been steady . . . "

Is the light still on or did it go out ?

There exists a GM Technical Service Bulletin, written for GM technicians, that pertains to 2007 Chevrolet Avalanche, Suburban, Tahoe, and 2007 GMC Yukon, Yukon XL models with NVG246 Transfer Case (RPO NP8).

The bulletin discusses an intermittent " Service Four Wheel Drive " message and a DTC (Diagnostic Trouble Code) CO378 set by the TCCM (Transfer Case Control Module).

The bulletin advises technicians to check specific terminal pins in a specific connector at the TCCM and to update the TCCM with the latest calibration.
Also, it advises that the vehicle should normally be driven in 2WD mode and to use Auto or 4WD modes when road conditions are appropriate.

Rocket science ? No, but it’s close. If your problem is intermittent and has CO378 set then your TCCM unit may need to be reprogrammed as outlined in the bulletin. Otherwise, it will have to be properly diagnosed (Probably starting with a code scan) by a rocket scientist or mechanic who understands this stuff to find out what went kaput.


In the 2003 trailblazer cleaning and reseating the Electric plug on the tranny was one solution.

Whether or not the service light is linked to the functionality light of the 4wd is questionable. It should not be. If it is, there is an electrical problem in the system as @csa indicates. So… When in 4 wd on a lift, you can rotate the wheels then the transfer case shaft to see what is truly engaged. If every thing works, it’s not an actuator but a position switch problem. This assume oll connections have been checked.

You never indicated that the vehicle actually failed to function as a 4wd when the lights did not go on. If it did, it again, is a position switch problem. If it did not, the actuators ( there may be two, transfer case and front differential) could be a problem. This often occurs from lack of service And/or lack of use. Get it serviced and use it frequently as the manual suggests.
. Bottom line…you should be using 4 wd often when you don’t need it so it will function when you do.

These switches and actuators are very suspetable to failure do to lack of use and service. The old manual ones with manual hubs just got stiffer to use. The automatic actuators just don’t have enough power when you neglect them… Sometimes, service (fluid change and use) is all that is needed. Sometimes putting in a warm garage can get it to work too…but it could be just temporary.

Most dealers have financing available for these kind of problems…

This particular transfer case has a lot of design flaws and is used in GM and Chrysler trucks. I’ve experienced similar problems that just magically went away. The t-case actuator, the sensor in that actuator and the switch are all common problems. The cheapest and easiest to replace is the switch. As the miles accrue, watch for oil spots colored blue from the middle of the truck. This indicates the oil pump inside the transfer case chewing its way out of the case. The pump wears the softer case and creates a leak. The prevention is to remove, disassemble and install a wear washer into the case. Once it leaks, it can be repaired with epoxy or replace the case. Either way, get prepared for a big repair bill.

Did you get help? On March 5th/2018 my 2007 Silverado Chev 4x4 “Service four wheel drive” light came on. It wouldn’t go into 4 wheel drive. On the 8th, it cost a pretty penny to have it fixed at a good dealership where I bought the truck. They have a service there and they are a huge company. I brought it home and 2 days later, the light came back on. I took it back and they said it was fixed but before I got off the lot, it came back on. Today is the 22nd (March 2018) and they said they put a new pin (s) in it. I think they calibrated it. They said the light is out bit they are driving it today, putting some miles on it to see if the light comes on. So far, 803.00$ and this time around I have no idea what it will cost. :cry: Any comments and all comments are welcome. The dealership is if anyone wants to check it. It is very reputable and that wehre we buy all our vehicles. If they are confused, well, there is little hope. Please comment, we need help. Thank you.

Only $803? Depending on what was done, that’s pretty reasonable for a new rear housing but that’s only needed if it leaks. It is a bit high for a new actuator, way high for a new t-case sensor-encoder, and wildly high for a new 4WD switch.

So what did they replace? And what do you think we can do to help?

You can argue that since you paid them $803 and they DIDn’t fix it, they shouldn’t charge you for this repair. I think that may be your only avenue.

You should also stop getting so upset about $800 for a repair. This was an expensive vehicle originally, it is 11 years old and guessing 100,000 plus miles, there are more of these types of repairs on their way. Front wheel bearings for one, brake hoses and pipes for another, fuel pump for a 3rd and all will be in the same neighborhood. Sounds harsh, but I’m trying to warn you. Start saving up now.

Geraldine can you tell us what they did to fixit? I have been driving mine for a year with “service 4 wheel drive” message. Yes I had it serviced and my mechanic tells me that nothing is wrong other than 4wd will not work (scan tool says “computer lost contact with transfer case” but all wires seem to be intact. He says just keep driving it. My Tahoe is an 07 and only has 80k on it. We seriously only drive it on Sunday to church. lol

What better advice do you expect ? Just ignore the message apparently you don’t need the 4 wheel drive.

Yes VOLVO, but i have been doing just that for the last year i have been getting this message. It is not a question of need its that i cant stand the thought of not having the 4wd working any longer. I guess I just have to take it to the stealership. They are gonna charge 110.00 dollars to scan to give me diagnosis. The good news is I will not have to pay that if I let them fix it. Hmmm makes me very suspect of the price they are charging to fix this junk.

You don’t need a dealer for an 11 year old vehicle. That 110.00 diagnostic fee is very reasonable .

Check and clean the connection where it plugs onto the trans, if applicable.

$110 / hour is pretty reasonable for dealership shop work. Don’t forget the dealership has to pay more than just the tech’s salary. The have liability insurance, fire insurance, employee health care benefits, rent for the lot, utilities, tool purchases, etc, all have to be added to the cost burden. Bottom line: If they aren’t able to make a profit, they won’t come to work. I presume they are estimating it will take one of their techs an hour of their time to provide an accurate diagnostic. If they can figure out what’s causing the problem for $110, seems a good deal to me. Much better than guessing.

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