“Service Four Wheel Drive”

Bill 1960

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Venting: It’s important for my use the transfer case Neutral position functions, because I bought this truck to tow behind our motorhome.

I tested it before I bought it in December. :waytogo:

I have operated it a few times since.

Today I hook it to the tow bar for a test run and when I put the selector to N I get “Service four wheel drive system”. :favorites68:

Leave it sit for five minutes and the message disappears. Everything works; 2H, Auto, 4H, 4L. Except when I try neutral again and the error message pops up. Rinse and repeat several times, same thing every time.

So, back in the garage. I’ll check the connectors in case the dealer left something loose when they replaced the transmission recently. No, the connectors look good, they even put dielectric grease in them. So, I cleaned out the plugs and sockets with contact cleaner, just in case there’s some grit or foreign material held by the grease that may inhibit a good contact. Aaaaand success! In and out of every position including neutral, just like clockwork. Repeatedly. :favorites37:

Back to the tow bar I go. Hook up the bars and all the umbilicals. Shift into neutral. “Service four wheel drive system”.

:rage:
 

Dantheman1540

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I had some odd electrical issues when I first bought mine and would hook up a trailer. It ended up being poor ground in the trailer wiring system, I added a ground and it fixed all the issues.

I diagnosed it by hooking jumper cables from trailer to hitch and having the problems go away.
 

Bill 1960

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Latest attempt after another rest period it worked. :hmm:

So now it’s an intermittent problem and I have trust issues.

Here’s a pic from the test run. Can’t have a thread without pics.
 

Geotrash

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Venting: It’s important for my use the transfer case Neutral position functions, because I bought this truck to tow behind our motorhome.

I tested it before I bought it in December. :waytogo:

I have operated it a few times since.

Today I hook it to the tow bar for a test run and when I put the selector to N I get “Service four wheel drive system”. :favorites68:

Leave it sit for five minutes and the message disappears. Everything works; 2H, Auto, 4H, 4L. Except when I try neutral again and the error message pops up. Rinse and repeat several times, same thing every time.

So, back in the garage. I’ll check the connectors in case the dealer left something loose when they replaced the transmission recently. No, the connectors look good, they even put dielectric grease in them. So, I cleaned out the plugs and sockets with contact cleaner, just in case there’s some grit or foreign material held by the grease that may inhibit a good contact. Aaaaand success! In and out of every position including neutral, just like clockwork. Repeatedly. :favorites37:

Back to the tow bar I go. Hook up the bars and all the umbilicals. Shift into neutral. “Service four wheel drive system”.

:rage:
If memory serves, there is a limit switch in the 4WD actuator that tells the system that the engagement/disengagement process if complete. I don't have my manuals in front of me, but can you be sure that the actuator is indeed working, regardless of the error message?
 

Bill 1960

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If memory serves, there is a limit switch in the 4WD actuator that tells the system that the engagement/disengagement process if complete. I don't have my manuals in front of me, but can you be sure that the actuator is indeed working, regardless of the error message?

When it works, you can hear the actuator working. When it malfunctions it doesn’t make a sound. As far as I can tell it’s not even trying to move.

I have all the schematics. But not a tech2. I’m done for today. After coffee tomorrow I’ll consider what course of action to pursue, whether to chase it myself or farm it out. Or do nothing. You can spend a lot of time and money chasing intermittently occurring problems.
 

Sam Harris

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I had this issue intermittently for almost 3 years, since I owned the truck. My 4hi / 2hi, etc.. would all typically work fine, but once in a while it would give me that “Service 4WD” message, and fail to change into any other setting. The final time this happened, I started it up one morning, and it said it was in 4lo, out of the blue, but was obviously not. I decided it was time to fix it. My tech2 reported a code: (I’ll have to dig up..) and I replaced the encoder ring. No issues since. Pretty easy / cheap repair. This is a very common problem.

ETA: code was a C0327
 
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2591tdj

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You might want to search this forum for older discussions on this subject. As I recall, there are a number of separate discussions that cover things to check. Mine got so bad that it would go into 4L or 4H by itself and was hard to get it out. It continually got worse until I found the solution, which is discussed in one of those earlier threads.
 

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