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Discussion Starter · #1 ·
Need help with this one. No 4wd. Do not get the 4x4 light when the ignition is turned to the ON position. I do get it while cranking along with the Low Range Light. I have the codes P1828, P1815 and P1865.
I have been reading other posts and came across a pinpoint diagnostic PDF but it looks to be for a different year.

Here is what I have done so far. Replaced the dash switch, checked for voltage at the shift motor.(made up a lead and checked it in the cab while moving the selector switch). Oh, checked all of the fuses related to 4wd(pulled and checked for continuity) I have voltage at 4 terminals at the relays(the same terminals on each relay. No signal to activate the coils.

Any suggestions?
 

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Discussion Starter · #3 ·
I will take a look at that.
 

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The only reason I ask is because my 4x4 didn't work for the longest time and my air was stuck on defrost. Come to find out, the pump that seals the vacuum for the 4x4 is also the same pump that switches settings. I replaced the pump and everything worked. How ever I'm not sure about the fail codes though.
 

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If you have manual backup hubs, engage them. If you still don't have 4wd, and you have voltage at the transfer case, then the motor in the transfercase is not working. If you don't have manual backup hubs, then most likely its just a vacuum leak in the hub system. This COULD be the issue even if your vents work normal. The automatic 4wd goes out eventually on EVERY truck of this vintage. My 08 is the same. The vacuum hubs eventually quit working, but like i said if you lock them in manually and still no go, it has to be the case motor.
 

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Discussion Starter · #6 ·
All of the vents work as they should.
 

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PROBABLY still a vacuum leak somewhere. But not bad enough to cause a "defrost only" situation.
 
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Disconnect the vacuum lines leading to the hubs and test the hub seals by pulling vacuum on the nipples with a pump (Mityvac, etc.). If they hold vacuum the seals are good, if not the seals are bad. Its an easy first step.
 

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Discussion Starter · #9 ·
I don't think it is the vacuum system. My hubs are auto and manual. Still not getting 4wd with them in manual.
 

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Then its something wrong with the motor on the t-case. Test to see if its receiving power in 4WD. If its not there's an electrical issue. If it is then the motor is bad.
 

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Discussion Starter · #11 ·
No power to the shift motor
 

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Power comes through the switch I would think, unless the switch switches ground. I would start troubleshooting there.
 

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ive got the ESOF in my 01 and the light wont come on ether but everything is working. Light only comes on in 4 low for me. But i also have Warn manual hubs.
 

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Be careful poking around the switch. You can fry you GEM module easily.

Sent from my SAMSUNG-SM-G870A using Tapatalk
 

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Discussion Starter · #15 ·
This truck doesn't have a GEM. It does have a 4wd control module. Would like to diagnose the problem further before replacing the module. I have seen a pin point diagnostic for the 4wd but it looks like it is for a different year.
 

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I would purchase a factory service manual on CD. They only cost about $60 and will have all pinpoint tests, etc. for your particular year.
 

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Scotts, My apologies on the misinformation. I had a 2000 and I have a 2003. They seem virtually identical and are in most ways. I fried the GEM in my 2000 trying to diagnose a similar issue to yours and I assumed the systems were the same.
 

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Discussion Starter · #18 ·
Thank you all for your responses. I would like to keep this thread going because there are others like me having the same kind of issues with their trucks. Or at some point will have problems. I have not come across many articles or threads that cover the problems associated with electrical portion of these 4wd's. Most of you know that these large trucks need their 4wd to get out of spots that other lighter trucks have an easy time getting out of in 2wd.
 
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