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P0562 Supply Voltage Fault

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Hi All,A while back I got codes P0491 and P0492 - Secondary Air Injection. Also had fault 31 Fresh Air Blower Fault. Not really sure how to diagnose I decided to remove the SAI motor to clean and re-grease the bearings. I re-installed and cleared the codes. I really didn't think this would fix the fault, but figured it was easier to do this than to try and find a vacuum leak. Everything was fine for about 400 mi, until today. Could be completely unrelated but I had the battery/generator dash light come on today as well as the CEL. Voltage kept dropping on my drive home. Gage probably read about 10.7 V at the end of the drive. Codes today are P0491 & P0492 (back again) P0562 - Supply Voltage and 24 - Air Con Power Supply. I checked the battery cables up front and the Pos terminal in back, all are tight and corrosion free. Checked the fluid level on the "maintenance free" battery, one cell was a little low, topped it off. So, I'm guessing my alternator has stopped working?? Any thoughts? I checked Pelican, alternators are expensive ~$450, I don't want to start randomly replacing parts w/o knowing it will fix the problem. Is the only way to check an alternator by removing it and taking it to the machine they have at Auto Zone?

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I would have your battery tested. While it's good your cables look tight and corrosion-free you would really need to test the voltages properly. Ahsai recently had a really nice write-up on how to do this... or a shop should be able to do it for you pretty quick. This wiring harness is a very common problem.

The alternator can be pseudo load-tested with it still in the car. This only takes about 10 mins. Otherwise if you get it out, Auto Zone or similar store should be able to test it for you. If the alternator is in fact bad, $450 seems a little high if memory serves. I would have thought more like ~ $350 or $375 for a Bosch reman depending on if you need the freewheel pulley version or not.........

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+1 on getting your alternator load checked. I had a situation where my alternator voltage would start out (cold engine/alternator) with a charging voltage of about 13.5 and droop to about 11.0 volts as the engine/alternator came up operator temperatures. Appearantly, voltage regulators have a heat related failure mode.

The fix was (after eliminating battery, ground/power cables) replacing the voltage regulator. A voltage regulator costs about $20.00-25.00 and can be replaced easily.....once the alternator is removed from the car. I, in fact, didn't work on the alternator. I took it to a auto-electrical shop recommended by my dealer. The shop had a new voltage regulator and installed it and tested it; part and labor $85.00 + tax.

Now my charging voltage is about 14.3 volts.


Edited by whall
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I removed the alternator with the Pelican instructions, it tested bad. It's probably just the voltage regulator, but I figured since I already had it all taken apart I ordered a reman alternator from Napa with a lifetime warranty for about ~$250. I really didn't want to have the regulator be the fix knowing that alternators have a finite lifespan. Plus the last two times I tried to do something more cheaply I didn't like the results. I did the cheap ignition switch fix, that worked for about 7 months before it failed again and I replaced the whole lock cylinder. Many people recommend Sumitomo III tires, I bought them since they are so cheap, but am not super happy with them. Oh, and when I changed plugs I didn't do coils, only to have 3 coils die a year later. With my luck, I've decided to be as complete as possible from now on when it comes to replacing parts / preventative maintenance.

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Had a similar issue some time back. Replaced only the voltage regulator which fixed the problem 90% but, in the end, it turned out the alternator was otherwise bad (would operate within spec except at certain RPM ranges)...and this may or may not have contributed to shortening the life of the voltage regulator. I don't regret trying that first as the alternator really isn't that tough to get to, but if I had to do it again I would just replace the alternator next time with a Bosch reman. I normally don't fix what isn't broke... but my alternator was 85K miles old and the alternator is a wear item, like most of the parts on the car...so sometimes I agree in doing the preventative maintainance. Either way, hopefully this gets you sorted.......

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