Replacing the voltage regulator on an alternator

Tiny
WESLEY NASH
  • MEMBER
  • 2012 HONDA CIVIC
  • 1.8L
  • 4 CYL
  • AUTOMATIC
  • 140,000 MILES
I would just like to ask if the voltage regulator on an alternator can be replaced for the car listed above? It has already been tested and it failed on the voltage regulator and if it sits too long my battery drains. The battery was tested and it is good.
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Wednesday, March 14th, 2018 AT 2:33 PM

4 Replies

Tiny
CARADIODOC
  • CERTIFIED MECHANIC
Yes, it is possible, but probably not practical. For sure you will not find a mechanic willing to do the repair this way. First you have to determine if you have a Mitsubishi generator or one made by Nippendenso, then you have to find the right parts. Given the mileage you listed, you will want to replace the brush assembly too as it is near the end of its life. If you reuse the old assembly, you will be doing the job over soon. The bigger problem with this design is there is no way to diagnose a failure to charge as caused by the voltage regulator. It is inside the generator where you cannot reach any test points.

The insane engineers have gotten out of hand with their use of unnecessary, unreliable computers to do things for which they were never needed before, but on your model, they took that to a whole new level. In the past, most manufacturers other than Chrysler packed the entire charging system into the generator. The advantage was everything got replaced when the generator was replaced, which pretty much insured a successful repair. The disadvantage was you bought the part you needed, plus the rest of the system that was not needed. On your car, part of the charging system is in the "battery sensor" by the battery, part is in the under-hood fuse box, some is in the engine computer, and there is a whole computer circuit in the instrument cluster just to drive the charging system warning light. Way too often we read where someone replaced the generator and still has the charging problem. You want to replace just a small part of the generator in hopes it will solve the problem.

If you are trying to solve a drain on the battery, that is not likely to be caused by the voltage regulator. Even if the regulator is shorted, the circuit is turned off by the ignition switch, so there could not be a drain through that part of the circuit.

The first thing we need to know is the charging voltage while the engine is running. If you find between 13.75 and 14.75 volts across the battery terminals, the regulator is working. Additional tests are needed to measure full-load output current and "ripple voltage", but those require a professional load tester.

The reason a mechanic will not repair a vehicle this way is first, it takes a lot of extra time to pull the assembly apart, order the regulator, replace the part, put it all back together, and hope the problem is solved. Sometimes special tools are required that shops do not have. The real problem is what to do when the problem is not solved? If the customer asked for the unusual service, he got what he asked for, and is obligated to pay for it, then the diagnosis has to start all over again. Even if the diagnosis was correct, if a mistake was made during the service, the mechanic will be expected to do the job over again for free. He loses the chance to move on to the next job. That waiting customer is going to be angry, and you will be angry that the job was not successful. We have enough trouble with undeserved bad reputation without inviting more frustration. To avoid that, it is usually less expensive to replace the entire assembly that was professionally-rebuilt and tested, and comes with a warranty. You will pay more for the generator, but a lot less for labor.

The cost of labor isn't an issue if you are going to do this yourself, but keep in mind I have done this type of repair on my own vehicles when I had plenty of free time, and as an expert who taught Automotive Electrical for nine years, I made my share of mistakes. I also observed all the ways students could make mistakes that resulted in the generators not working properly. You will not have the luxury of having me looking over your shoulder and offering advice. I applaud you for wanting to try to do this repair, especially given the really high cost of a replacement generator, but my fear is this will turn into another unsuccessful attempt. There is too much computer circuitry outside the generator, and I do not think I will be able to help with understanding how that works.
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Wednesday, March 14th, 2018 AT 3:33 PM
Tiny
WESLEY NASH
  • MEMBER
Thank you for getting back with me. I guess I will be getting a new alternator. My wife said how about a junk yard and I told her I would only be getting someone else's headache. But again thanks.
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Wednesday, March 14th, 2018 AT 3:49 PM
Tiny
CARADIODOC
  • CERTIFIED MECHANIC
Did you check the charging voltage? Please keep us updated on your progress and/or success.
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Wednesday, March 14th, 2018 AT 3:58 PM
Tiny
WESLEY NASH
  • MEMBER
I sure will and will do so Saturday.
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Wednesday, March 14th, 2018 AT 9:33 PM

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