I recently bought a 2014 Dmax having dropped back to an older pre dpf vehicle for the common reasons. I did'nt test the 4x4 until I got the vehicle home and out on a bush trail. The 4x4 engages in both high and low range but warning lights come on the dash and an alarm beeps for the low range. NRMA came up with this fault code and advised me to head to the transmission specialist in town, who couldn't diagnose the fault and recommended the local auto electrician business. The auto electricians had the vehicle for the day and didn't find what the fault was. My nearest Isuzu dealer if almost 2hrs away and booked out for at least a month and after asking the auto electricians if they believed an Isuzu garage would be able to find the fault, they just smiled.
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.
Ivan 01 said
11:35 AM Dec 2, 2022
Just spoke to an auto electrician mate of mine and his first question was,
*Has the vehicle been in a flood or under water*?
DeBe said
11:36 AM Dec 2, 2022
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.
Ivan 01 said
12:08 PM Dec 2, 2022
Hi again JonP
There is some info in this google search link. Some of this I have already suggested as to have the code cancelled and drive it again to see what happens. The rest gets a lot more technical.
It's Norwegian, and it's for a 2012 D-max, but there is a section on the transfer case starting on page 102. I think I can recognise two switches and an actuator.
Page 107 has a list of diagnostic test codes (DTC).
-- Edited by dorian on Friday 2nd of December 2022 02:19:49 PM
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.
[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
deverall11 said
07:07 PM Dec 2, 2022
Dmax forum. Usually those forums are a encyclopaedia of information from actual owners.
Lots advice also.
JonP said
07:09 PM Dec 2, 2022
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.
This may, of may not, be helpful but my previous vehicle was a Holden Jackaroo all of which was made by Isuzu except the Holden badge. The Jackaroos, including mine, had a common fault which was that a limit switch on the transfer case would fill with mud and fail to correctly report 4WD state resulting in a dash light flashing when the vehicle was placed into 4WD. It's is possible that issue now results in an error code being generated?
dorian said
08:15 AM Dec 3, 2022
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?
JonP said
10:19 AM Dec 3, 2022
dorian wrote:
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?
My thoughts exactly but I was advised I would have more luck on here getting to the bottom of it.
Ivan 01 said
12:25 PM Dec 3, 2022
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.
dorian said
01:04 PM Dec 3, 2022
JonP wrote:
dorian wrote:
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?
My thoughts exactly but I was advised I would have more luck on here getting to the bottom of it.
As far as I'm concerned, it should be easy to at least determine, conclusively, whether the problem is with the switches. Just interchange them and observe the new error code. If the error remains the same, then the problem is in the wiring harness or the computer. If the error code changes, then the problem is the switch. Is that too hard (for a transmission specialist or an auto electrician)?
Of course, I'm assuming that the actuator is doing its job and moving the fork in the transfer case, as your observations would suggest.
-- Edited by dorian on Saturday 3rd of December 2022 01:20:57 PM
Ivan 01 said
01:26 PM Dec 3, 2022
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.
dorian said
01:51 PM Dec 3, 2022
Ivan 01 wrote:
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.
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.
Ivan 01 said
02:26 PM Dec 3, 2022
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.
travelyounger said
08:33 PM Dec 3, 2022
JonP wrote:
I recently bought a 2014 Dmax having dropped back to an older pre dpf vehicle for the common reasons. I did'nt test the 4x4 until I got the vehicle home and out on a bush trail. The 4x4 engages in both high and low range but warning lights come on the dash and an alarm beeps for the low range. NRMA came up with this fault code and advised me to head to the transmission specialist in town, who couldn't diagnose the fault and recommended the local auto electrician business. The auto electricians had the vehicle for the day and didn't find what the fault was. My nearest Isuzu dealer if almost 2hrs away and booked out for at least a month and after asking the auto electricians if they believed an Isuzu garage would be able to find the fault, they just smiled.
Hi
I had the same problem with my 2017 dmax when new.I took it to a reputable dealer in port Lincoln which does Ford Izuzu and other brands of vehicles which was a total waste of time as the exspurts there had no clue what the problem was.
Next dealer I went to was north east izuzu in Adelaide which is a large fleet dealership which only do izuzu trucks and vehicles.
The mechanic took me for a short drive and within a minute of going through all the 4wd high and low range settings said it was most probably the actuator and since now done 160000 km and never had a problem unless you go into low range when not in neutral mine being an auto transmission .
If you do not follow the procedure for low range then these alarms will come on hope this helps
Cheers
RickJ said
11:02 AM Dec 7, 2022
dorian wrote:
Ivan 01 wrote:
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.
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.
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 recently bought a 2014 Dmax having dropped back to an older pre dpf vehicle for the common reasons. I did'nt test the 4x4 until I got the vehicle home and out on a bush trail. The 4x4 engages in both high and low range but warning lights come on the dash and an alarm beeps for the low range.
NRMA came up with this fault code and advised me to head to the transmission specialist in town, who couldn't diagnose the fault and recommended the local auto electrician business. The auto electricians had the vehicle for the day and didn't find what the fault was. My nearest Isuzu dealer if almost 2hrs away and booked out for at least a month and after asking the auto electricians if they believed an Isuzu garage would be able to find the fault, they just smiled.
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.
*Has the vehicle been in a flood or under water*?
Hi again JonP
There is some info in this google search link.
Some of this I have already suggested as to have the code cancelled and drive it again to see what happens.
The rest gets a lot more technical.
https://www.yourmechanic.com/article/p0839-four-wheel-drive-4wd-switch-circuit-high-by-yourmechanic
You can cancel your codes by disconnecting your battery for about half an hour. Youll lose your radio presets too.
I found this manual:
https://docplayer.me/storage/20/648482/1669952444/fqcA180Pzfhd-0czNsqOtg/648482.pdf
It's Norwegian, and it's for a 2012 D-max, but there is a section on the transfer case starting on page 102. I think I can recognise two switches and an actuator.
Page 107 has a list of diagnostic test codes (DTC).
-- Edited by dorian on Friday 2nd of December 2022 02:19:49 PM
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
Lots advice also.
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.
Go to the Google Play Store and search "Check Engine Light" - sometimes it's just too hard to post links to this obtuse forum.
engine-codes.com/make/isuzu/1
This may, of may not, be helpful but my previous vehicle was a Holden Jackaroo all of which was made by Isuzu except the Holden badge. The Jackaroos, including mine, had a common fault which was that a limit switch on the transfer case would fill with mud and fail to correctly report 4WD state resulting in a dash light flashing when the vehicle was placed into 4WD. It's is possible that issue now results in an error code being generated?
My thoughts exactly but I was advised I would have more luck on here getting to the bottom of 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.
As far as I'm concerned, it should be easy to at least determine, conclusively, whether the problem is with the switches. Just interchange them and observe the new error code. If the error remains the same, then the problem is in the wiring harness or the computer. If the error code changes, then the problem is the switch. Is that too hard (for a transmission specialist or an auto electrician)?
Of course, I'm assuming that the actuator is doing its job and moving the fork in the transfer case, as your observations would suggest.
-- Edited by dorian on Saturday 3rd of December 2022 01:20:57 PM
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.
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.
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.
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.