Alternator diode test
#1
#4
I would not recommend removing the battery cables while the car is running. While this test works on older cars without a hitch, modern cars are more sensitive to such things. Damage could occur to the computer modules.
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ant17 (09-19-2021),
motorcarman (09-18-2021)
#5
#6
#7
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#8
Up to about 1992, Jaguar had external devices to prevent alternator voltage rise when the battery is disconnected and from about 1993 on, the protection was included in the alternator's voltage regulator.
In any case, I would not disconnect the battery with the engine running on any modern car without first checking that this is o.k. to do.
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Samilcar (10-19-2021)
#10
Shut the car down and remove the power cable from the stud on the 'false-bulkhead' to see if the drain is in the alternator.
The power wire goes from the power stud to the starter and then a short link to the alternator.
Pull the large wire and it shuts power to BOTH starter and alt.
The power wire goes from the power stud to the starter and then a short link to the alternator.
Pull the large wire and it shuts power to BOTH starter and alt.
#11
#12
Essentially a 1 amp draw is huge! Do you have anything that’s aftermarket installed in the car?
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
Last edited by Addicted2boost; 09-19-2021 at 04:49 PM.
#14
Essentially a 1 amp draw is huge! Do you have anything that’s aftermarket installed in the car?
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
Tests across fuses. No relay tests.
Battery definitely NOT the problem.
I use the remote to lock the doors, but sometimes leave it unlocked. If I use the key, the buttons will go down or up.
#15
When you turn the ignition off and pull the key out, do you hear a sharp “snap”? There’s a little door that closes where the ignition key was. If that door doesn’t close when you pull the key out, the modules won’t go into sleep mode because the car thinks there’s a key in the ignition and will cause an excessive current draw.
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ant17 (10-11-2021)
#16
When you turn the ignition off and pull the key out, do you hear a sharp “snap”? There’s a little door that closes where the ignition key was. If that door doesn’t close when you pull the key out, the modules won’t go into sleep mode because the car thinks there’s a key in the ignition and will cause an excessive current draw.
#17
When you pull the key out pin 4 to pin 5 makes contact or loses contact ( i gotta check as this is way back in the wiring guide )
See page 78 upper left corner
X300 98/E COVER (jagrepair.com)
This can be checked at the ignition switch connector
easy the get to the connector as the small U shaped cover under the steering column
This starts the SLCU to go through the steps to finally go to sleep
One of the steps is repositioning the steering column to exit the vehical
To bypass this step rotate the knob on the column from auto position to off
You could have a dragging steering column that never reaches the exit position which the SLCU looks for an agreement as a checklist to go to sleep
The alternator can be removed and the auto parts store can spin it up on a machine and see the diodes if they pass or fail
If you turn the stereo to a AM station you should be able to hear a bad diode package ( 4 in a rectifier bridge ) change pulses with engine RPM
See page 78 upper left corner
X300 98/E COVER (jagrepair.com)
This can be checked at the ignition switch connector
easy the get to the connector as the small U shaped cover under the steering column
This starts the SLCU to go through the steps to finally go to sleep
One of the steps is repositioning the steering column to exit the vehical
To bypass this step rotate the knob on the column from auto position to off
You could have a dragging steering column that never reaches the exit position which the SLCU looks for an agreement as a checklist to go to sleep
The alternator can be removed and the auto parts store can spin it up on a machine and see the diodes if they pass or fail
If you turn the stereo to a AM station you should be able to hear a bad diode package ( 4 in a rectifier bridge ) change pulses with engine RPM
Last edited by Parker 7; 10-10-2021 at 11:27 PM.
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ant17 (10-11-2021)
#18
The diode package can be changed inside the alternator assembly
This is a source not knowing your part #
I am assuming the X308 alternator is a Denso manufacture
You can also get other alternator parts like brushes , bearings , voltage regulators on their site
Denso (Nippondenso) Series Alternator Rectifiers (alternatorparts.com)
This is a source not knowing your part #
I am assuming the X308 alternator is a Denso manufacture
You can also get other alternator parts like brushes , bearings , voltage regulators on their site
Denso (Nippondenso) Series Alternator Rectifiers (alternatorparts.com)
Last edited by Parker 7; 10-11-2021 at 01:25 AM.
The following users liked this post:
Addicted2boost (10-11-2021)
#19
Essentially a 1 amp draw is huge! Do you have anything that’s aftermarket installed in the car?
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
If your answer is no, in my experience of current draws in these cars, these are the most common components of failure for excessive draw.
Body processor module (BPM)
Security locking control module (SLCM)
Door module. There’s 1 in each door.
Excluding the alternator, what have you done so far to try and diagnose or narrow down your excessive current draw? Do you lock the car door with the key and all the locks pop up and down? There is also a timeframe in which all the modules go into “sleep mode” after you lock the car. I find that 30-60 minutes is the norm and that’s when the ma number for the draw is at the most accurate.
Last thought. How old is the battery and is it a good quality one? Sometimes when I perform a draw test I need to use a new battery just to rule out the possibility that the battery itself isn’t the issue of giving me a false draw number.
#20
The BPM and SLCU can be reset by a Jaguar hard reset
There are stereo head unit security code ( lock out from use ) precautions though
The BPMis behind the glove box
SLCU is by the trunk left hinge ( behind the side liner ) and is mounted at a slight angle
I think its the side liner as you can remove the fwd liner as this one is easy
The BPM must be programed with software if replaced and there is a tag with the software version in the engine compartment by the front windshield
There are stereo head unit security code ( lock out from use ) precautions though
The BPMis behind the glove box
SLCU is by the trunk left hinge ( behind the side liner ) and is mounted at a slight angle
I think its the side liner as you can remove the fwd liner as this one is easy
The BPM must be programed with software if replaced and there is a tag with the software version in the engine compartment by the front windshield
Last edited by Parker 7; 10-11-2021 at 02:53 PM.