I dont have a list defining the fault codes but the detail should be available.

Now having said that maybe the NRMA should or maybe could have cancelled the warning and then have you operate the vehicle again to see if the warning re occurred.

Many times a warning may appear due to a simple thing like an electrical surge or anything where the vehicle computer may be activated to report a fault. The code reads something within the 4wd switch and its circuit. Maybe a faulty switch or a switch with high resistance for some reason. (just guessing out loud)

A quality Scan Gauge if you decided to buy one, may give you the opportunity to diagnose and cancel rogue warnings.

First thing I would consider is if the vehicle is operating correctly in 4wd regardless of the warning lights.

I would try a phone call to the dealer service manager.
My basic thoughts are that if the auto trans specialist referred you to an auto electrician then the transmission is probably ok and it is an electrical fault. The dealer may know if it is a common problem in that model.

Did you buy the vehicle locally as the auto elec may have already had a look at it for the old owner or seller.

Good luck with it.

First item you should have is a workshop manual with circuit diagrams. They are avalable relativly cheap on the internet, hard copys or PDF files. Even if you dont know what you are looking at you may find some one who can help you. Since its a second hand vehicle i would be looking for that switch & its wiring. The switch may be faulty (can be tested) Or the wiring to it is damaged (repairable) or its plug has been riped apart 4 wheel driving. Most garages are not going to be interested in pursuing a repair due to lack of information (they wont be interested in purchasing a Workshop Manual) The cost of a workshop manual to you is nothing compared to what a mechanic is going to charge in hourly rates.

You can cancel your codes by disconnecting your battery for about half an hour. Youll lose your radio presets too.

If there are two identical transfer case switches, would it make sense to interchange them, assuming they test OK? If the error code doesn't change, then you've eliminated the switch as a cause.

I would think that you would test the switch by depressing the ball and measuring the resistance at the terminals with a multimeter.

I expect this is what they look like:

https://lzd-img-global.slatic.net/g/p/ab30606b913b34cf9031a268e5746095.png

This article describes what a "history DTC" is:

https://www.autoserviceworld.com/carsmagazine/taking-a-first-look-at-permanent-dtcs/

[History DTCs] are readings that were out of parameter before, but aren't out of range now. After a certain number of "clean" trips -- trips when a fault doesn't reoccur -- a "current" DTC will become a "history" DTC. These can still be cleared in the usual way, after the data is recorded and you're sure you won't need it. The important thing here is not to erase information that could speed up diagnosis.

If you want to determine which switch is responsible for the C0391 code, then disconnect the plug from one of the switches and operate the 4WD selector. I expect that C0390 is the error for the other switch. Of course, after you do this, the error will become a "Current DTC" until it is eventually cleared by normal driving.

-- Edited by dorian on Friday 2nd of December 2022 05:18:57 PM

Thanks for the reply's guys, I will try and find the switch and have look.

Back to the beginning, Ive only just bought the vehicle so have no idea if its been flooded. In saying that I was fed a list of lies about every part of its description and ownership. I feel very embarrassed for falling for it to be honest.

NRMA did clear the faults and got me to test, which instantly through the faults again.

The vehicle does work in both high and low range 4x4 but instantly throughs faults and warnings. These simply go after turning the ignition off then back on.

Its become a money pit which Ive gone to far with to walk away from, also I could not pass this on to anyone knowing the things I still need to rectify. Im fixing things one at a time and trying not to look to far ahead. There are cracks through the engine bay, crushed fuel tank, crushed sump, wiring twisted together with poorly wrapped tape holding, melted wiring, faulty lights, holes Ive pushed through the sills with my fingers. Im trying to be positive a work on through it.

 

Cant find your specific code

engine-codes.com/make/isuzu/1

If both a transmission specialist and an auto electrician were unable to locate the fault, then it's unlikely to be a simple switch problem. Or is it?

I feel after seeing your following posts JonP, that if it was a simple switch replacement then it would have already been replaced.

Your most recent description, I feel, holds the cause to the problem.

You said this;

Im fixing things one at a time and trying not to look to far ahead. There are cracks through the engine bay, crushed fuel tank, crushed sump, wiring twisted together with poorly wrapped tape holding, melted wiring, faulty lights, holes Ive pushed through the sills with my fingers. Im trying to be positive a work on through it.

From this it sounds like a lot of expense unless you fall upon the fault and fix by sheer luck.

Maybe bite the bullet and move it on for a vehicle in a more reliable condition.

Vehicle wiring and the vehicle computer can be quite illusive as to the real cause of a fault code.

While we could all respect the desk technician directly connected to a google source JonP should not ignore the fact that the Code is indicating the High range Circuit switch while the warning alarm is sounding when the vehicle is actually in low range.

Another strong hint of a deeper problem is in this statement.

The auto electricians had the vehicle for the day and didn't find what the fault was.

To me as a retired automotive mechanic, this indicates to me that it was a strong possibility that the auto elecs didnt want to get involved in something that has been butchered. This thought of mine is compounded by JonPs complete description of the overall condition of the vehicle.

 

JonP, swap the switches by all means or even buy one new switch as a substitute of known quality but really a conversation with the auto elec asking them what was tested would eliminate the need for duplicating their work.

Obviously the best results would be that the auto elecs didnt do any testing and it is in fact a faulty switch but the code description certainly doesnt indicate this.

Good luck with it Jon.

Maybe you could then message the OP and offer your assistance in the flesh.

From my limited experience ( if compared to yours) the wiring could be causing many problems.

He certainly needs the valuable assistance of an expert.

It is a shame you didnt relay your experience in the electronic field of automotive electrical before the rest of us made any comment or at the very least, in your first reply.

JonP it sounds like Dorian ( not his real name) is your best bet if relying on anyone from this forum to solve your problem.

Leave it to ya Dorian.

dorian wrote:

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Ivan 01 wrote:

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While we could all respect the desk technician directly connected to a google source JonP should not ignore the fact that the Code is indicating the High range Circuit switch while the warning alarm is sounding when the vehicle is actually in low range.

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I have repaired many automotive ECUs and other automotive gear (digital dashboards, climate controls, digital speedometers, radios). My local mechanic, and my local auto electrician, both used to send me their electronic jobs. That said, narrowing the fault to either a switch or a circuit is not hard. It's made even easier by comparing the good circuit against the bad circuit. The hard part is waiting for the fault to reappear, if it is intermittent.

I have a simple procedure to test the circuit, if the OP ever gets to that point. I expect that if one unplugs the switch, there will be 5V between the terminals at the end of the harness. Inserting a 1K or 4K7 resistor between the terminals should drop the voltage. Comparing the voltage drops between the two circuits will tell you if either circuit has excessive resistance.

If it turns out to be a computer problem, the first thing to look for are ESD protection diodes on the sensor inputs. If these are bad, then simply removing them should restore full function, albeit without protection.

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Being a relatively new member on here I have been reading back over past topics.

It is funny that I have noticed the hat the majority of your contributions on any topic contain a Google link.

I imagine that based on this most people would consider you a desk bound google quote type of forum guy.

No one would assume that in this topic you are actually a vehicle computer expert.

I wonder did the op get the problem fixed.