I was away, but I'm back. The ESOF PVHS is on the passenger fender, next to the starter relay. You will see two vacuum lines going into it and a two-conductor connector. Here is the vacuum diagram. [LINK]

This is from the reapair manual:


The vehicle does not shift between 4X4 and 4X4 LOW modes correctly

• CJB fuse 59 (30A).
• MSS.
• Park/neutral position switch.
• Brake pedal position (BPP) switch.
• 4WD control module.
• Transfer case.
• Digital transmission range (TR) sensor.
• Anti-lock brake control (ABS) module.
• Circuitry.

There are a bunch of tests that stem from that point. I don't suppose you have a code reader... errors like this usually throw a code.

 

What does mss mean?

And how can I test the neutral position switch and bpp sw?

 

any takers? I'm back from Holidays and want to get this thing fixed up. I have to take it out on the road for work in 3 weeks.

Also, do the headlights go through a relay(s)?

my low beams and running lights now don't work now too and I need to have that resolved too.

I'm thinking that maybe in my relay swapping for the 4 hi/low and low hi stuff I put a bad one in the low beam spot.

 

Ok just went out and did some testing...

Meter shows my circuits to be functioning like they should be.

Unplugged and hitting the motor with 12v i can get it to engage 4x4 hi and disengage 4x4 hi...
It will try to lock in 4x4 low but peters out.

I can lock into 4x4 low manually with a wrench and it functions wonderfully...

My issue is a weak motor.

 

gotta bring this up again. The problem was never resolved.

Couple questions it would be helpful for me to know.

what does MSS stand for?

And how can I test the neutral position switch and bpp sw?

Are they grounds?

Also, all my lights started working again after that one post but it seems my running lights and dash lights stopped working again. Everything associated with the headlights (running/highbeam/lowbeam etc) all function properly. all signals and brake lights function properly as well. I have zero dash lights and no tail running lights though.

also with that diagnostic checklist that tugly posted for why the 4lo won't work. The ABS module is listed as a possibility. I get the ABS dash light coming on intermittently from time to time. That might be worth checking. Where is the ABS module located?

I'm thinking I have a bad module making all these issues. maybe even more than one bad module.

i love the truck but this is getting ridiculous with the electrical issues.

oh and my trailer light system is fubared. the brake controller usually doesnt provide power to the trailer brakes and my lights are all wacko. trailer brake lights don't work. Left signal makes the right signal go. right signal doesnt work at all. etc etc. The tail lights on the truck work properly, except for this no running lights thing that just started.

Do all these things run through the VSM?

 

MSS (I believe means Multiple Selector Switch)is the selector switch for your 4x4.

I had similar issues with a truck have weird problems and it was related to a loose connection in the GEM module, but for you it is probably a loose/bad/chaffed connection somewhere along the way. I tested everything and it came up ok with power coming in and out as it should. Replaced the 4x4 shift motor and then 4x4 worked for a day. Next day it didn't. If the motor is weak it will cause problems as well and may test fine.

I would think a relay or fuse is bad. Just for kicks have you checked your battery power while the truck is running. I've seen bad batteries or alternators cause all kinds of weird problems even tho the trucks seems to run fine.

Either way I would chase down all the other electrical issues before moving on to the 4x4. I would think a relay is bad/going bad somewhere.

Where are you located?

 

I'm up in thunder bay ontario.

I'm going to assume the alternator is fine since it charges everything perfectly. The batteries are only a couple years old and they are really high quality ones. Most of these issues started when I had different batteries in the truck and putting in new ones made no difference.

And that's the plan. I mean no 4lo is annoying but it is pretty secondary to no running lights or dash lights at this point. I'm taking the truck off the road next week to do a bunch of work and I'll be pulling a whole lot apart in search of an answer to my problems. There are a few poorly wired things from before I bought the truck and I want to clean that up anyway.

 

Did the running light blow out? Are you sure your alternator is overcharging? Does it have any show any alternating current that's out of the ordinary?

 

No everything remains steady like it always has. Nothing is unusually bright or dimming and surging.

And no they didn't blow out. The tail lights are leds and all the same ones light for the running lights as the brake lights and the brake lights work. Even if something did blow out back there my dash lights went out at the same time. And the door chime doesn't kick on if I leave the switch on with the key removed. I'm going to check the fuses but that may be a bad switch. I'll have a look at it today

 

one of the guys posted a site that has a lot of wiring diagrams for our trucks. It's search.ebscohost.com. User name: marshall; Password: public. Hope that helps.

 

Awesome thanks. I'm headed out of town for the long weekend so I'll be tearing into the truck next week and maybe try to find some problems and fix them then

 

I got problems, too.

I found this while looking for wiring diagrams and thought it may help you.

Transfer Case — Electronic Shift
The four-wheel drive electronic shift on the fly feature electrically shifts the vehicle transfer case between
2WD, 4X4 HIGH, and 4X4 LOW. The system mode is selected by the operator through mode select switch
(MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument
cluster indicators, one for 4X4 HIGH which is 4X4, and one for 4X4 LOW which is LOW RANGE (in 4X4
LOW both the lamps are on). Shifts into 4X4 HIGH can be made at any speed. When shifting into 4X4 HIGH
with the vehicle stationary, tooth blockage may occur preventing shift completion. When the vehicle is driven
above 8 km/h (5mph) the shift will complete. When shifting into or out of 4X4 LOW, the generic electronic
module (GEM) requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and
the transmission in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual
transmission). (The digital transmission range [TR] sensor informs the GEM when the transmission is in the NEUTRAL range position)

So if your truck is starting in any gear, it don't know when it is in neutral and will not command the 4lo shift.

 

Agreed. But I don't know the protocol for checking the range sensor wire. Like, is it 12v in neutral or does it ground out in neutral? I don't know.

Also, my truck doesn't have a gem. It has a vsm and a 4wd module. I assume the neutral wire goes to the 4wd module.

 

I think these trucks use a more complex switch for determining what gear is selected than just an old style one or two wire neutral safety switch. I'll see what I have on it.

 

How high did the water get. Did the vsm get wet?