Battery charge light will not turn off
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Joined: May 2021
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Honda Prelude Si 4WS
Battery charge light will not turn off
I am having really big trouble with my 1991 Honda Prelude and it's getting to the point where I am starting to feel like I want to get it towed to the wreckers. I don't really want to do that but it's really taking the cake.
I hosed down my engine bay and the battery warning light came on and then an hour later my battery went flat. So far, this is what I have done to try and fix the problem:
- Checked the alternator fuses
- Fully charged the battery
- Replaced the alternator with a remanufactured unit
- Replaced the crankshaft pulley
- Replaced the drive belt
Today I checked the replacement alternators' B terminal with a multimeter and it's reporting just 3.84 volts! I thought perhaps the belt was slipping so I tightened it but it made no difference.
The only thing that I haven't checked is the air conditioner compressor pulley.
This could be a hint but it could also mean nothing... when I first installed the replacement alternator, the battery charge light no longer came on but the drive belt was squealing really loud. Then half an hour later, the squealing stopped and the battery charge light came back on again and has been on ever since.
What do others think?
I hosed down my engine bay and the battery warning light came on and then an hour later my battery went flat. So far, this is what I have done to try and fix the problem:
- Checked the alternator fuses
- Fully charged the battery
- Replaced the alternator with a remanufactured unit
- Replaced the crankshaft pulley
- Replaced the drive belt
Today I checked the replacement alternators' B terminal with a multimeter and it's reporting just 3.84 volts! I thought perhaps the belt was slipping so I tightened it but it made no difference.
The only thing that I haven't checked is the air conditioner compressor pulley.
This could be a hint but it could also mean nothing... when I first installed the replacement alternator, the battery charge light no longer came on but the drive belt was squealing really loud. Then half an hour later, the squealing stopped and the battery charge light came back on again and has been on ever since.
What do others think?
Thread Starter
Newbie
Joined: May 2021
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Honda Prelude Si 4WS
Today I used a multimeter to perform tests on the alternator. I hope someone can tell me why the alternator is putting out 3.88 volts only.
All tests were carried out with the engine running at 800 RPM except for the last rectifier test, and the battery cable was disconnected from B terminal.
B terminal with alternator connector connected:
3.88 volts between B terminal and engine
3.89 volts between B terminal and battery negative post
-7.9 volts between B terminal and battery positive post
6.8 millivolts between alternator housing and battery negative post
B terminal with alternator connector disconnected:
0.93 volts between B terminal and engine
0.94 volts between B terminal and battery negative post
-9.74 volts between B terminal and battery positive post
0.64 millivolts between alternator housing and battery negative post
Alternator terminals (grounded to engine/grounded to battery negative post):
IG: Nil/6.2 volts
S: 3 volts/3 volts
L: Nil/6.4 volts
FR: Nil/6 volts
Alternator connector (grounded to engine/grounded to battery negative post):
IG: 11.5/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49/11.5 volts
FR: 11.81/11.82 volts
Alternator rectifier test with engine running:
Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -240 millivolts
Alternator rectifier test without engine running:
Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -933 millivolts
All tests were carried out with the engine running at 800 RPM except for the last rectifier test, and the battery cable was disconnected from B terminal.
B terminal with alternator connector connected:
3.88 volts between B terminal and engine
3.89 volts between B terminal and battery negative post
-7.9 volts between B terminal and battery positive post
6.8 millivolts between alternator housing and battery negative post
B terminal with alternator connector disconnected:
0.93 volts between B terminal and engine
0.94 volts between B terminal and battery negative post
-9.74 volts between B terminal and battery positive post
0.64 millivolts between alternator housing and battery negative post
Alternator terminals (grounded to engine/grounded to battery negative post):
IG: Nil/6.2 volts
S: 3 volts/3 volts
L: Nil/6.4 volts
FR: Nil/6 volts
Alternator connector (grounded to engine/grounded to battery negative post):
IG: 11.5/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49/11.5 volts
FR: 11.81/11.82 volts
Alternator rectifier test with engine running:
Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -240 millivolts
Alternator rectifier test without engine running:
Multimeter positive probe to B terminal/Multimeter negative probe to alternator housing: Nil
Multimeter negative probe to B terminal/Multimeter positive probe to alternator housing: -933 millivolts
Last edited by Kolusion; May 27, 2021 at 10:09 AM.
Thread Starter
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Honda Prelude Si 4WS
I just tested the voltage between the following:
Battery positive terminal and battery negative terminal
Battery positive terminal and engine
Battery positive terminal and alternator
All results matched, so the problem can't be bad grounding.
Does anyone know what else could be the problem?
Battery positive terminal and battery negative terminal
Battery positive terminal and engine
Battery positive terminal and alternator
All results matched, so the problem can't be bad grounding.
Does anyone know what else could be the problem?
Thread Starter
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Joined: May 2021
Posts: 8
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Honda Prelude Si 4WS
I think I may have found a clue. S should be 12 volts, have a look at S in the charging system circuit diagram.
http://media.honda.co.uk/car/owner/m...f100/16-66.pdf
Now have a look at my test results of the alternator connector.
IG: 11.5 volts/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49 volts/11.5 volts
FR: 11.81 volts/11.82 volts
S isn't even hitting 6 volts, so there is resistance either in the wiring or the fuse. Does anyone know if this is of significance?
http://media.honda.co.uk/car/owner/m...f100/16-66.pdf
Now have a look at my test results of the alternator connector.
IG: 11.5 volts/11.52 volts
S: 4.58 volts/4.58 volts
L: 11.49 volts/11.5 volts
FR: 11.81 volts/11.82 volts
S isn't even hitting 6 volts, so there is resistance either in the wiring or the fuse. Does anyone know if this is of significance?
Last edited by Kolusion; May 27, 2021 at 11:06 AM.
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Thread Starter
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Joined: May 2021
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Honda Prelude Si 4WS
So the diagrams in the shop manual for the alternator terminals and the alternator connector are pretty crap and I thought the diagrams were of the alternator terminals but they are actually of the terminals in the alternator connector. I realised when the result I was getting on the multimeter from S at the under-hood fuse box wasn't corresponding with the result I got yesterday from S on the alternator connector. These are the correct test results from yesterday of the alternator terminals and alternator connector.
Alternator terminals (grounded to engine/grounded to battery negative post):
L: Nil/6.2 volts
FR: 3 volts/3 volts
IG: Nil/6.4 volts
S: Nil/6 volts
Alternator connector (grounded to engine/grounded to battery negative post):
L: 11.5/11.52 volts
FR: 4.58 volts/4.58 volts
IG: 11.49/11.5 volts
S: 11.81/11.82 volts
I don't know if the FR circuit to the ECU is 12 volts, but if it is then there appears to be a problem somewhere in the FR circuit.
To rule out the FR terminal in the alternator connector being bad, I followed it's WHT/RED wire to it's socket at the top right hand side of the engine bay, disconnected the connector that connects to the socket and then tested the FR terminal inside the connector.
https://i.ibb.co/0Y1ShrJ/FR-at-top-r...-connector.png
These are the results:
FR at alternator connector: 4.55 volts
FR at top right hand side engine bay connector: 4.94 volts
What do others think?
Alternator terminals (grounded to engine/grounded to battery negative post):
L: Nil/6.2 volts
FR: 3 volts/3 volts
IG: Nil/6.4 volts
S: Nil/6 volts
Alternator connector (grounded to engine/grounded to battery negative post):
L: 11.5/11.52 volts
FR: 4.58 volts/4.58 volts
IG: 11.49/11.5 volts
S: 11.81/11.82 volts
I don't know if the FR circuit to the ECU is 12 volts, but if it is then there appears to be a problem somewhere in the FR circuit.
To rule out the FR terminal in the alternator connector being bad, I followed it's WHT/RED wire to it's socket at the top right hand side of the engine bay, disconnected the connector that connects to the socket and then tested the FR terminal inside the connector.
https://i.ibb.co/0Y1ShrJ/FR-at-top-r...-connector.png
These are the results:
FR at alternator connector: 4.55 volts
FR at top right hand side engine bay connector: 4.94 volts
What do others think?
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