Voltage drop on negative side (alternator)
06-08-23, 08:05 AM
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Voltage drop on negative side (alternator)
I have a GX470 with 170,000 miles. A year ago I had some parasitic drain issues with the battery dying overnight. Solved eventually with new ECU thanks to help from this page.
In the last couple months, my car would drive just fine and then if I stopped anywhere and restarted, it would be dead. I’d jump it and be on my way to next stop and repeat until I could put it on the charger overnight. I got in the habit of just carrying my trusty jumper as well as an extra new battery out of the fear of being stranded. The overnight drawn did not return as I could leave it a week and it would still crank. Just not after driving.
two weeks ago, I was driving about an hour and pulling a less than 1k pound trailer and ended up on the side of the road. One of the pulleys had lost thread, the nut fell off and the belt too -ending up with some overheating and bubbling in the coolant. Towed to shop where a new belt and pulley were replaced and water pump checked out “ok” and a new radiator cap. I considered maybe this had been causing some alternator charging issues and was so happy that my expensive tow and repair might eventually solve the problem.
I was able to make it home the next day pulling trailer about an hour and no over heat but felt like low power. Parked car to unhook trailer and immediately went to restart to move it and it was dead. Jumped it again.
battery connections are tight and clean and well troubleshooted from the last battery drain issue. Battery from 10/22 and test good at auto store. Voltage at battery after charging over night is 12.9. At idle it remains at 12.9.
voltage between b post and housing is 14.26.
b post and pos terminal is .05
b post and b post cable is 0.0
battery pos and battery pos cable is 0.0
b post and fuse box 0.02
fuse box and battery 0.1.
should there be 0 at both ends of the b post to battery pos cable or does that just means a good connection?
on the negative side, the neg batt post to alternator body is -1.24 but all the other tests are 0.0.
The alternator is newly installed last October when I was troubleshooting the previous issues.
Any suggestions as to further troubleshooting or cause?
In the last couple months, my car would drive just fine and then if I stopped anywhere and restarted, it would be dead. I’d jump it and be on my way to next stop and repeat until I could put it on the charger overnight. I got in the habit of just carrying my trusty jumper as well as an extra new battery out of the fear of being stranded. The overnight drawn did not return as I could leave it a week and it would still crank. Just not after driving.
two weeks ago, I was driving about an hour and pulling a less than 1k pound trailer and ended up on the side of the road. One of the pulleys had lost thread, the nut fell off and the belt too -ending up with some overheating and bubbling in the coolant. Towed to shop where a new belt and pulley were replaced and water pump checked out “ok” and a new radiator cap. I considered maybe this had been causing some alternator charging issues and was so happy that my expensive tow and repair might eventually solve the problem.
I was able to make it home the next day pulling trailer about an hour and no over heat but felt like low power. Parked car to unhook trailer and immediately went to restart to move it and it was dead. Jumped it again.
battery connections are tight and clean and well troubleshooted from the last battery drain issue. Battery from 10/22 and test good at auto store. Voltage at battery after charging over night is 12.9. At idle it remains at 12.9.
voltage between b post and housing is 14.26.
b post and pos terminal is .05
b post and b post cable is 0.0
battery pos and battery pos cable is 0.0
b post and fuse box 0.02
fuse box and battery 0.1.
should there be 0 at both ends of the b post to battery pos cable or does that just means a good connection?
on the negative side, the neg batt post to alternator body is -1.24 but all the other tests are 0.0.
The alternator is newly installed last October when I was troubleshooting the previous issues.
Any suggestions as to further troubleshooting or cause?
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SlowRider1
ES - 1st to 4th Gen (1990-2006)
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09-05-11 12:16 PM