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Discussion Starter #1
Thought you would be interested. My RR is in GB fault again. Over the
last
couple of weeks, I have been noticing a slight dimming of the dashboard
lights in the evening and I wondered if something was going to happen.
In case you don't remember, I replaced all of the battery cables and the
battery in May 2010.

I ran the tests again and it looks like the alternator is not putting
out
enough voltage.

results:

1. engine off, all accessories on for 30 seconds, then off. voltage was
12.5 volts
2. Voltage across battery at idle (no load) 13.5 volts
3. Voltage across battery at 2000 RPM (no load) 13.44 volts
4. Voltage across battery at 2000 RPM (everything switched on) 13.28
volts
5. Voltage at ALTERNATOR at 2000 RPM (everything switched on) 13.36
volts
6. Voltage drop between alternator body and battery negative (YES
negative)
max electrical load and 2000 RPM was 64.5 mv
7. Voltage drop between alternator positive and battery positive at 2000
RPM, max electric load was 50.7 mv
8. Check voltage drop from battery negative terminal to 1st groundpoint
on
vehicle-voltage was 21 mv
9. Check voltage drop from 1st ground point to block- it was 44 mv
10. Check voltage drop from alternator housing to block-19 mv
11. voltage from Alternator positive to alternator housing- it was 13.5
volts

Should I buy a new or rebuilt alternator? Have I made the correct
diagnosis?
thanks have a great day!
 

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Your positive and negative wires are working fine. You have fixed those.

Your alternator is not putting out sufficient voltage.

In the sticky, I say not to rebuild or buy an aftermarket alternator. A lot of people were having problems due to this. However, I see absolutely no reason why any decent alternator will not work properly. If you decide to go aftermarket or whatever, you should know how to test it and MAKE SURE it is working properly from the moment it is installed. If it is not working properly and you don't find it, you'll just kill your battery and have to replace the cheapo alternator and the expensive battery.

Over the life of the P38, the alternators kept getting bigger. From memory 100amp --> 120 amp --> 150 amp.

Don't be afraid to get a big one. It should produce between 14.2 to 14.4 volts at high loads (with the help of 2000rpm to do it).

The easy answer is the largest genuine alternator that will fit your car will make your problem go away. I have no doubt there are much cheaper solutions that will totally fix your problem too - if you can be bothered.

Mine was rebuilt some years ago and has worked fine since. My problem however was not resolved by the rebuild. It was the wires you have already replaced that was the real problem. I spent a lot of money batteries and alternator repairs to find it out, which is why I researched and wrote the sticky to save everybody else.

Greg
 

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I had very poor grounding on my 98 RR HS 4.0 litre. So I followed the sticky tests exactly and pinpointed the problems. I then cleaned all the ground connections and added some 4 gauge wire between the battery and alternator. Retesting showed that this had fixed my ground problems.

I then took the vehicle for a test drive and noticed that dreaded "Gearbox Fault" message had disappeared. However, shortly after the test drive the message came back. But not wile driving like it used to. Now it shows up immediately after I park and turn off the ignition.

There is also a very noticeable clunk from what I think is the gearbox or front transfer case (I'm not sure which since I don't know much about the RR's mechanics) when gearing down from 3 to 2 and from 2 to 1. Still, this makes me think my "Gearbox Fault" message might actually be a real fault, rather than an electrical fault.

Anyone have any ideas about the clunk? (my apologies for potentially hi-jacking this thread)
 

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Niblettes, an electrical problem could cause the kinds of symptoms you are talking about. I guess an actual gearbox problem can too.

I would start by going over the sticky again and posting all results here. You need a good battery AND a good alternator AND good wiring. Each should be fully tested again and post answers here. If that isn't the problem then you might need to start a new thread.
 

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Thought I would mention this. Years ago i had my truck worked on and i experienced all of the symptoms you are describing. Turns out mechanic routed the serpentine belt incorrectly and it was not getting enough power to the alternator. So before I got heavy in to the other stuff I would check the routing and shape of your belt.
 

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wrldky,
I think this is how my belt goes:


ghind,
I had some bad grounding and fixed it by adding some 4 gauge wire. Here is a link to my post about tracing then fixing my grounding problems according to the sticky:
http://www.rangerovers.net/forum/viewto ... 4&start=15

Just to make it a bit easier, here are the latest results:
0. Engine off, no accessories
today: 12.31

1. Engine off, all accessories on for 30 seconds, then off. What voltage:
1st----------2nd----------DELTA -------- 3rd Test Today
12.48--------12.63------- +0.15 -------- 12.15

2. Voltage across battery at idle (no electrical load):
1st----------2nd----------DELTA -------- 3rd Test Today
14.13--------14.32------- +0.19 -------- 14.30

3. Voltage across battery at 2000rpm (no electrical load):
1st----------2nd----------DELTA -------- 3rd Test Today
14.15--------14.34------- +0.19 -------- 14.30

4. Voltage across battery at 2000rpm (everything electrical switched on):
1st----------2nd----------DELTA -------- 3rd Test Today
12.35--------12.32------- -0.03 -------- 12.96

5. Voltage at ALTERNATOR at 2000rpm (everything switched on):
1st----------2nd----------DELTA -------- 3rd Test Today
14.37--------12.44------- -1.93 -------- 13.20
(I left the full electrical load running for the following tests because the instructions didn't specify removing the load)

6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm:
1st----------2nd----------DELTA -------- 3rd Test Today
0.455--------.075-------- -0.38 -------- 0.093

7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load:
1st----------2nd----------DELTA -------- 3rd Test Today
1.320--------0.134------- -1.186 ------- .135

8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle:
1st----------2nd----------DELTA -------- 3rd Test Today
12.60--------0.110------- -12.49 ------ .003

9. Check voltage drop from 1st ground point to block:
1st----------2nd----------DELTA -------- 3rd Test Today
0.376--------.063-------- -0.313 ------- .023

10. Check voltage drop from Alternator Housing to block:
1st----------2nd----------DELTA -------- 3rd Test Today
-0.002-------0.002------- same --------- .002

11. Voltage from alternator positive to alternator housing:
1st----------2nd----------DELTA -------- 3rd Test Today
14.24--------12.35------- -1.89 -------- 14.35

Voltage after shutting down and waiting a minute:
1st----------2nd----------DELTA -------- 3rd Test Today
12.59--------12.88------- +.29 --------- 12.81

I've also checked that battery drain with the vehicle off:
When I first connect my multimeter with one reading light on: 1.216 A
After a few seconds when the door lights extinguish: 0.972 A
After turning off reading light: 0.628 A
After 2 minutes: 0.035 A

So it seems that there is no unusual drain on the battery while the vehicle is off.

The battery itself has 995 cranking amps and 795 cold cranking amps and is about 5 months old.
 

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Your battery voltage at rest of 12.15 volts is way to low

This is very likely to be related to the cause of your gearbox faults.

The allowable ranges are shown in the sticky. These ranges are not approximate. They are the allowable range.

The battery should still be 12.5 volts after 30 seconds of electrical load then a short resting time with no charging in between. i.e. vehicle off the whole time

You have insufficient charging or a dud battery (or both).

What is your results for test 4 with just the high beam headlights, rear demister and max fan blower switched on?

I would also give the battery 24+ hours on a high quality 8 amp 3 stage or better charger then use the car as normal and run the tests again a week later.

Greg
 

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Ok, I replaced the battery and it now hold over 12.58 after 30 seconds of full electrical load. So that's good. But it didn't do anything for the gearbox problem.

I have been noticing a couple other odd behaviours related to the gearbox i'd like to share to see if anyone might have any ideas of the cause.

So again the problem is I get a nasty clunk when the transmission gears down from 3 to 2 and again from 2 to 1.

I've also noticed that the "Sport/Manual" button doesn't work. I push and nothing happens. Except sometime, and only the RR is completely cold, when I hit it, it will light red and display an "S" in the message center. Somtimes I can drive a while and it will remain on, other time as soon as I step on the brake to shift from P to D it will disable the "Sport" mode.

I also noticed that when the "S" is displayed in the message, and only when the "S" is displayed, the message center will also display the gear I'm in. At no other time will the selected gear be displayed in the message center. And when I when the sport mode button goes dead, and the "S" disappears from the message center, so to does the selected gear.

Any one out there with any ideas (I'd rather ask here first before asking a mechanic -- "have any idea?" is the most expensive question you can ask a mechanic).
 

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I'm only guessing, but if it were mine I'd borrow another gearbox ecu. It is strange that electronic functions only work when cold and the gearbox will not operate properly if the gearbox ecu fails. I think it will go into a limp home mode which gives the kinds of symptoms you are talking about. 999 times out of 1000 that is caused by weak battery/charge circuit but there could be other triggers.

Also, what are your results for test 4 now? When you turn everything on, just turn on your high beams, blower fans to max and rear demister.
 
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OK, good news, I had to move the truck out of the garage tonight to work on another car and the GEARBOX fault went away! The only possible thing I did that may have affected it was I removed the ABS ECU overnight then reconnected it a day later. So I am going to get a voltage reading on all of the Trans ECU pins since they are still exposed and see if any are different from when the truck was showing the GB fault. I'll let you know. Thanks for the ideas and encouragement so far.
 
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Sorry to bother you again, I thought I had a recent success when I removed the ABS ECU and examined the connector, tested for continuity, etc...I then reconnected the ABS ECU and a day later the Gearbox fault went away!!
It has been 3 or 4 days since and we have driven it several times with no issues (other then the MIL for the check engine). Last night, I went to Autozone and used their OBDII reader to obtain the CEL code (it was P1606) Immediately after I took the code reading, it showed the Gearbox fault again. So I am back to square one and seeking advice. Thank you for any assistance.
Brian
 
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Update: I have removed the Becm, trans ECU, ABS ECU and the engine ECU. I opened all of them up and removed a few transistors, most of the capacitors and a few diodes. I tested them and have ordered replacement parts. Some of the transistors and capacitors were bad and most of the diodes were OK. I will be reassembling the ECUs soon and will update.
 

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Finding bad capacitors especially in circuit is pretty difficult. I am impressed. Did you look for corrosion/fuzz/burnt spots, or do you have a schematic? We could all benefit from schematics if you have access to them.
 
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Capacitors are so inexpensive that I removed them, tested them and replaced all of them. I found several that were "bad" but a couple were still good. I decided to replace all of them anyway. I also removed the relay from the TCU pcb and tested it. It was malfunctioning. I am waiting for that relay (it was shipped earlier this week) after I replace that I will put it all together and see what happens.
 
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I returned the ECUs and started it up. The Gearbox fault was still present. I drove it to the end of the driveway and shut it down, then restarted it and the Gearbox fault had gone away! I went for a test drive and shut down a couple of times and restarted it. The gearbox fault has not returned! At this point I have to assume the relay in the TCU and some of the other electrical components were bad. If the GB fault returns, I will post again. I still have a CEL illuminated so that is the next issue I need to resolve.
 
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I used an OBD2 code reader loaded onto a laptop and a connector from a outfit in Hong Cong and the stored codes were P1775 and P1606. We cleared the codes and I have been driving it for a couple of days now without any CEL or GB fault. It looks like we successful!
 
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