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Premium Member
1995-2002 Range Rover P38A
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Discussion Starter #1
Since I couldn't find much on these forums for this code, I thought I make a post with my symptoms, troubleshooting, and hopefully the results when all is said and done. So let's first start with the symptoms.

Symptom: When I was idling at a stop light or in park, my engine would just die. Upon which I would turn the key to start it and it would fire right back up. There was never an instance that it would not fire back up. So this ruled out a few things like the CPS and what not. I didn't have the reader on me at the time and waited when I got back home to look to see what happened and if any codes were thrown. I get back and only 1 code came up, P0562.

P0562: Measurement Circuit OK Battery Voltage Low Fault
20180805_140222.jpg Screenshot_20180805-191815_Photos.jpg

Took a look around nanocom and noticed that the Battery (V) was jumping around which I found odd See above picture, or here:https://www.youtube.com/watch?v=zfS0EzxXlmw since the voltage at the battery itself seemed stable (albeit low, but stable).

So, I decided to just do the normal battery/charging tests outlined on this site and everything looked decent except the battery voltage and the charging voltage. The drops across the cables and the various grounding locations were all about 40-50mV. So, I thought I would do a quick data collection of the battery and charging voltage to see if some load was kicking on that was dropping the battery voltage too low thus becm shutting the engine off or something. So I did a quick capture and annotated what certain points are which events. See the following:
VoltageMatlab_marked.jpg

My battery is about 6 years old now and not even sure on the alternator as it's never been touched since I've owned the vehicle. So because of the low observed voltages, I'm going to put a new alternator in and also a new battery since mine is slowly on it's way out. Also, yes... I have a very very small leak from eas tank i need to finish tracking down. The compressor is also due for a rebuild.

My hope is that this is just a low voltage problem, but would be curious if anyone else has had a P0562 pop up and what the did to solve it? Also, on the nanocom, the "Battery (V)" voltage that is being reported, where is that coming from? My guess is that it's some internal measurement on the Becm?

I'll update this post with results.

2001 P38 HSE. 4.6L
 

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Registered
1995-2002 Range Rover P38A
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768 Posts
Rather than buying a new alternator, why not replace the brushes in the regulator, only a few dollars, a tiny bit of soldering and there done, my alternator was throwing out 10v, back to 14.5 now and running nicely for £5.
you can buy replacement regulators, but the genuine ones are the best to get, even an auto electrician should only charge around 25$ to replace the brushes, takes minutes to remove the regulator
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #3
Actually planning on taking it apart and re-building it myself. That way when I get the time, I can break it down all the way and replace most, if not all of the consumable parts in it. Due to time constraints on my end and the need for the vehicle, I just don't have the time at the current moment. So as Murphy's law has it, these things usually happen at the best time :dance:
 

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1995-2002 Range Rover P38A
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1,422 Posts
If you have put a meter directly on the battery and have seen the same wild fluctuations, then you have a very bad battery.
However, if the battery voltage is stable (and I suspect it is ) then you have a loose / corroded connection somewhere important, like between the engine and the battery and or frame.
Find the issue before you go chucking alternators and whatnot at it.
Start with all the large cables and work your way down in size checking ALL B+ and earths, especially as pertain to the BECM power.
Looking at the battery voltage graph, it does look like the alternator could be low, but this could also be a cabling issue.
How's the old fuse box? had a new one recently? Lots of potential for trouble there!
Happy Hunting!
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #5
Hey Bolt, thanks for the reply.

I definitely don't see the fluctuations at the battery. The alternator is definitely low and is my first item to get sorted out. Even at 2k rpms, it'll be putting out 13.5-13.6V with and without load. So before doing some more troubleshooting, I wanted to get this sorted out first.

If that "Battery (V)" reading from the nanocom is true, I'll have to hunt down where it's getting that reading from. Right after testing the various voltages from the charging circuit, I made some measurements on the fuses and wires I could access from the BECM fuse box location. All measured fine. I feel confident that the low voltage from the alternator isn't a cable issue as I measured that as well and only saw ~40mV drop on the cable. I double checked most of the ground points under the hood, but will pull up RAVE and make sure I double check them all once I get my charging circuit in order.

I rebuilt the fuse box myself about 5-6 months ago and it has been running tip top since. I guess there is always the potential that something in there went south. That's why I had the initial question of where the Nanocom was getting that voltage reading from? Since that code indicates the voltage is dropping out somewhere, I was hoping to be able to observe where that is happening, but haven't found the location yet.

But as with most things, I will get the charging circuit in order first so I don't have that possibly working against me.
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #6
Well I think it got worse? Now it cranks, but won't start. After replacement, I get P0562, but now with the following:
P0562 = battery voltage not plausible drive cycle A occured 1 times. Signal Missing. Fault is currently present. Fault determined as a persistent. fault does not cause the mil lamp activation.

I went through and checked the grounds and all should now check out. Any thoughts on where I might be able to measure the missing voltage?

20180808_185230.jpg 20180808_185247.jpg
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #7
I appear to have RPM when i'm cranking and the tooth count goes up. I'm still thinking this may be a voltage problem somewhere. Being able to drive it this weekend is looking bleek :|

Also, Murphy's law is having fun with me today.
20180808_205253.jpg :clap::clap:
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #8
Fixed the sweet Nanocom. Poking around rave and some other documents, and when I get some more time and sunlight out again i'm gonna check Connector 1 pin 7 on the Bosch Motronic ECU to see what i'm kind of voltage I'm getting at the thing
MotronicECUConnector1.PNG 20180808_214501.jpg

Sorry for all the posts. Trying to keep a log of what I've done.
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #9
Updates!

Before looking into this again tonight. I noticed this morning that I couldn't hear the fuel pump run when the key was turned. Checked the fuel pressure and also didn't see it go up. Manually made the pump come on, and it ran and built pressure fine. So this pointed out something on the ECM to me.

MotronicECM.jpg

My first order of business was to track down where that voltage was being read. As the previous post stated, I narrowed it down to one of those power wires by just looking through the electrical schematic in RAVE. First located the connector and unplugged it to take a look at it. Look "ok" but I cleaned it up any ways. Plugged it back in, and the voltage showed the same thing on the Nanocom. The battery supply (Pin 7 C0634. Orange-brown wire) measured fine both floating and with a load applied. Then I back probed pin 8 on C0634 which is "Main relay switched supply".

20180809_175922.jpg 20180809_175949.jpg 20180809_180932.jpg 20180809_180924.jpg

AH HA!!! Showing the same low voltage! According to rave, this showed the voltage can be "0-12V". So, I traced this wire back to see where it was coming from. Snippit from RAVE:
C0634.jpg

Looking at this schematic it was clear that RL19 is what fed the ECM Battery V voltage reading on the nanocom. So it was pretty straight forward from here. Pin 8 C0634: 2.2V. Pin 3 C0572: 2.2V. F 37: 12.6V. There you have it... Something slowly screwed up in the fusebox I rebuilt. :? . Also worth noting that I took the time to ohm out all of the grounds and checked the connections. To confirm this, i back probed pin 3 on C0572 (Bottom of fuse box) and fed it battery voltage with a powerprobe. I saw that the "Battery (V)" on the nanocom was now reading correctly. So, cranked it over while feeding it battery voltage and she fired right up!

So next thing I'm gonna do is to pull my box and take it apart again to see what went wrong. Hopefully my rants help someone on here in the future. Even though the fusebox is typically the culprit for odd electrical problems, I like to do what I can and track down the real cause of the problem. I learn a lot more from the process too :thumb:. Once repaired, I'll probably make a final post showing the results. Cheers.
 

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1995-2002 Range Rover P38A
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Ah HA!
The old "I just fixed that, it couldn't be that" Syndrome......Right up there with "Its a' brand new battery! Couldn't be that..."
Congratulations, and thank you for being so thorough! I like the way you approach troubleshooting. I can also appreciate the fact you want to fix stuff rather than just chucking in a new part.
So, in the end, the stalling was probably the fuel pump shutting off, ya think?
Cheers!
 

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Premium Member
1995-2002 Range Rover P38A
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250 Posts
Discussion Starter #11
Evening Bolt! Yea, i think that's exactly what was happening. I'd need to look, but I think there are some other things that rely on that voltage too. Either way, the fuel pump was just one of the things I could quickly test. I even pulled the fuel pump relay to make sure it was getting the signal correctly to turn on (which it was). It just didn't have the juice to actually run.
 
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