Service 4wd Comes On When Crow Hopping

[vester]

I have a 2007 Suburban 4WD. Previously I had the Service 4WD message and brought it to the dealer. Codes C0327 and C0378 were present. The dealer reflashed the TCCM per TSB #070421002. That fixed my issue at the time where the vehicle would not go into Auto, 4HI or 4LO.

 

Now, the vehicle will go into any selection, but if I get any binding while turning in Auto or 4HI, the lights start flashing on the switch and it reverts back to 2WD and I get the Service 4WD message. If I stop and put the transmission in neutral at this point and attempt to shift to 4LO, I can hear the transfer case engage. However, the light for 4LO just flashes for one minute or so and never completes the shift. Next, I selected 2HI again and felt/heard the transfer case shift. Previously, I have been able to turn off the vehicle and when it starts next, I can put it into 4HI or Auto and it will work until the front axle binds up again.

 

I am suspecting that it may be the front axle engagement actuator. From what I understand, the transfer case is shifted first and then the front axle is engaged.

 

I am still under my certified used B2B warranty and have an appointment at the dealer on Tuesday. Has anyone else had a similar issue? If so, what did it take to fix it?

[vester]

I have a 2007 Suburban 4WD. Previously I had the Service 4WD message and brought it to the dealer. Codes C0327 and C0378 were present. The dealer reflashed the TCCM per TSB #070421002. That fixed my issue at the time where the vehicle would not go into Auto, 4HI or 4LO.

 

Now, the vehicle will go into any selection, but if I get any binding while turning in Auto or 4HI, the lights start flashing on the switch and it reverts back to 2WD and I get the Service 4WD message. If I stop and put the transmission in neutral at this point and attempt to shift to 4LO, I can hear the transfer case engage. However, the light for 4LO just flashes for one minute or so and never completes the shift. Next, I selected 2HI again and felt/heard the transfer case shift. Previously, I have been able to turn off the vehicle and when it starts next, I can put it into 4HI or Auto and it will work until the front axle binds up again.

 

I am suspecting that it may be the front axle engagement actuator. From what I understand, the transfer case is shifted first and then the front axle is engaged.

 

I am still under my certified used B2B warranty and have an appointment at the dealer on Tuesday. Has anyone else had a similar issue? If so, what did it take to fix it?

 

I took it into the dealer today and go what is essentially a load of crap from the service adviser. The code in the computer was C0378. The dealer tells me that I shouldn't drive the truck in 4WD on dry pavement (which I don't, but it shouldn't matter) and that they could not reproduce the vehicle failing back to 2HI. They also told me they did NOT put it in 4WD because the roads are dry.

 

They gave me TSB# 07-04-21-002 (Attached): Intermittent Service 4 Wheel Drive Message Displayed in DIC, DTC C0378 set. The TSB concerns the front axle actuator retracting with key off and not cycling quick enough and generating an error. It seems to have nothing to do with my issue other than the code being mentioned.

 

The dealer offered to have a tech ride along with me, but they want the roads to be wet or snowy. My plan right now is to find a gravel lot nearby, replicate the problem and then make a tech ride with me while I cause the error.

 

Can anyone give me some insight or ideas on how to deal with this? Are there any other TSBs that might apply?

TSB_for_4WD_binding.pdf

TSB_for_4WD_binding.pdf

TSB_for_4WD_binding.pdf

TSB_for_4WD_binding.pdf

[BrockwayMT]

You should not get any binding in auto.

 

Did your dealer relearn the transfer case? That's the first thing I would do. They can force it to relearn with a tech2. You can also do it manually in the cab of the truck.

[vester]

You should not get any binding in auto.

 

Did your dealer relearn the transfer case? That's the first thing I would do. They can force it to relearn with a tech2. You can also do it manually in the cab of the truck.

 

 

I don't know if the dealer did a relearn or not. Last month, they updated the TCCM firmware, but I don't think they did this time.

 

When I was in Auto, I didn't feel any binding. After I accelerated from a stop light, I looked down at the switch. 2HI was steady and Auto was flashing, Service 4WD message in the DIC. After restarting the vehicle, I was able to shift through all 4WD settings.

 

I took the truck out yesterday to a gravel lot and was unable to get the Service 4WD message to come on or kick out of 4WD. I think the dealer may have followed the TSB and confirmed the mechanical action of the front axle actuator and disconnected/reconnected the electrical connector. I am going to do some more testing today to see if I can induce the issue again.

 

Just to be clear though, I should be able to drive in 4HI on dry pavement without the transfer case shifting on its own to 2HI? I understand that there will be reduced economy, binding in the axles and possibly accelerated wear on the tires and driveline, but I think it should still stay in 4HI as long as I want it to.

 

Thanks for the input.

[BrockwayMT]

You can drive on dry pavement in auto. You shouldn't drive in 4HI on dry pavement. You should get crowhop and binding. If its in 4HI it should stay there and not come out.

 

Do a tight turn on dry pavement in 4 HI. You should get crowhopping and binding. Do your tight turn in 4HI and stop (probably won't need much brake if any) with the truck bound up. Hold the steering wheel in positon and hold the brake. Turn the switch t0 2HI or 4 auto. The transfer case should gradually release over a period of a second or two. You'll feel the truck tilt a little as the suspension unloads. If the truck unloads violently or not at all something is wrong with the transfercase clutch settings. Often a relearn will fix it if. If not something is wrong with the tcase, actuator, or module.

[vester]

You can drive on dry pavement in auto. You shouldn't drive in 4HI on dry pavement. You should get crowhop and binding. If its in 4HI it should stay there and not come out.

 

Do a tight turn on dry pavement in 4 HI. You should get crowhopping and binding. Do your tight turn in 4HI and stop (probably won't need much brake if any) with the truck bound up. Hold the steering wheel in positon and hold the brake. Turn the switch t0 2HI or 4 auto. The transfer case should gradually release over a period of a second or two. You'll feel the truck tilt a little as the suspension unloads. If the truck unloads violently or not at all something is wrong with the transfercase clutch settings. Often a relearn will fix it if. If not something is wrong with the tcase, actuator, or module.

 

Thank you. I will give this a try today.

 

You said the TCase relearn could be performed from the cab. Do you know the procedure?

[BrockwayMT]

I sent you a PM. Let me know if you don't get it.

[vester]

I finally got my issue fixed. I don't think the binding had anything to do with the issue. I think it was moisture because the failure only happened in the rain or snow. The dealer was able to get the front axle actuator to fail using the tech 2, so they replaced it. I got them to do this by using my digital video recorder to record the message on the DIC and the refusal of the vehicle to return to 4WD or Auto after the error was set.

 

The paragraph below is from TSB 06-04-21-006A, it is the exact behavior I was having.

 

The C0378 - Front Axle Switch Malfunction and C0379 - Front Axle Control Circuit Malfunction DTCs operation is the same as the previous model utilities C0379 fault. If the Front Axle Switch input shows that the front axle is not engaged, the 2H1 lamp will light solid, and the requested 4WD mode lamp (4H1, AWD or 4L0) will flash. The shift will be blocked.

 

If this condition occurs in 4LO, the transfer case will be in low range without the front axle engaged. If it occurs in AWD, AWD will not operate.