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I've had a few problems after driving my longsuffering 1997 RAV4 on a bad dirt road including a shallow river crossing, and I think they're related and something to do with the electrics, but I can't figure out what they mean:

  • A couple of times when steering slowly at night, particularly reversing into my driveway, the steering locks or freezes for a second and then is very heavy. Some research suggests this could be the electric power steering motor cutting out because it's not getting enough power with the headlights, brake lights etc all on (and possibly a passenger using the power windows, I don't remember)
  • The stereo has started misbehaving, sound quality degrading to crackles after a few minutes use and intermittent cutting out. Some research suggests this is associated with struggling alternators.
  • Sometimes when starting the engine, there's a whistling or whining sound for several seconds, similar to an old style kettle or steam engine pressure valve letting off steam but oscillating. Some research suggests this could be the alternator or power steering motor whining, and it seems to come from the right direction for both. It's intermittent and hasn't happened with the bonnet up to identity more precisely.
  • I think the headlights are slightly dimmer and power steering slightly slower than usual but I could be wrong about these.

So I was expecting to find a slipped alternator belt or evidence it was failing and outputting low voltage, but I found something else:

  • The belts were fine and spinning fine with the engine at idle
  • The voltage at idle was 14.7, higher than expected. Didn't change while revving
    • I'm also not sure if this is "a little higher than normal but within the tolerable range" or "a seriously abnormal sign of a serious problem", different sources seem to contradict each other on this
  • The voltage of the battery itself with the negative terminal disconnected was 13.7, higher than expected. The circuit with the engine off was lower but less than 0.1 volts lower, within rounding. Something like 20 minutes after idling the voltage was down to 13.4 but still higher than expected, then immediately after running the engine again, it's back up to 13.7
    • Again, I'm not sure if this is "a little higher than normal but within the tolerable range" or "a seriously abnormal sign of a serious problem", different sources seem to contradict each other on this
  • With the battery connected and engine off, if I connect my multimeter negative cable to one particular spot (the steel air conditioning high pressure tube), it gives an unexpected voltage of about 0.4 volts which disappears when I disconnect the battery negative terminal. I'd expect either the same voltage as everywhere else, or zero. With the engine running this strange other circuit is something small like 0.03 volts higher

I feel like all this things seem related but I'm not sure how since it's the opposite of what I expected. What further tests can etc can I do? And are there any urgent things I should worry about e.g. Battery acid overheating?

  • Double check that not only the belts are moving but also the pulleys they're driving are spinning constantly, even under load, e.g. when turning the wheel with the car not moving. – JimmyB May 13 '17 at 11:21
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  • It seems that 1997 RAV4 has hydraulic power steering, not an electric one. If even there is an electric motor/actuator there, the power would have to drop really low for you to notice, so low that you would have trouble starting the engine next morning. Nothing in the car has even remotely comparable electricity draw as the starter.
  • if the stereo problems are related to time of using the stereo rather the time of using the car, this suggests a problem with stereo itself.
  • the high-pitched sound might come from starter clutch not engaging and what you hear is the starter overrevving.
  • I'd blame psychology here. Once you're convinced there are problems, you'll talk yourself into taking everything as evidence to corroborate.

voltage at idle was 14.7

That's textbook reading.

The voltage of the battery itself with the negative terminal disconnected was 13.7

Again, what a battery freshly disconnected from charging should read. A perfectly charged cell has 2.2V, hence a brand new battery should read 13.2V when fully charged. It should settle down a bit (to about 12.7V) after a day of lying around without being connected to anything.

it gives an unexpected voltage of about 0.4 volts which disappears when I disconnect the battery negative terminal. I'd expect either the same voltage as everywhere else, or zero.

With the engine running this strange other circuit is something small like 0.03 volts higher

Ohm's law. When there is a current flowing, it creates a voltage drop. It means that something is drawing current though that route and that's what you're reading. It's reading higher with the engine running because the power supply is slightly higher. I have no way of telling if the current should be flowing that way or is wrong. Eg a part which served as designed negative route is missing, lose or lost contact.

I'd expect either the same voltage as everywhere else, or zero.

No, if a current is flowing, there is a voltage everywhere. Albeit, it should be very tiny, because the receiver is getting voltage that much smaller. You should try disconnecting things to find out what draws the current you're measuring. The higher resistance (worse) the route and the higher the current draw, the higher the voltage drop will be. You can keep one lead at the battery and use the other to play hot or cold. The closer to the battery, the smaller the voltage should be, and the closer to the mystery consumer, the higher and sideways = no change. This way you may be able to pinpoint what draws this power.

My overall impression is that the electrical system seems to be very healthy for 20 years old car. With careful maintenance or a new battery, that's expectable.

As for the other symptoms, I think they come from unrelated issues, or maybe that dirt and fording caused several independent problems.

  • Note that power steering pumps often have a pressure regulator to deliver consistent power at different RPM ranges. As they get old they can sometimes stick "open" resulting in the kind of intermittent power steering loss described when the engine goes suddenly from high RPM to lower RPM. Changing the power steering fluid might help. – Perkins May 30 '18 at 0:52
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This sounds like it could be a faulty voltage regulator as you have symptoms of both over-charging and undercharging. Overcharging can fry some components and damage your battery, undercharging can lead to you losing power when you need it. I think that the regulator is actually part of the alternator on this car, you'd have to take the alternator apart to get at it, it may make sense to replace the alternator instead unless you are a pretty confident mechanic and have the right tools. New ones seem pricey, you might be able to get a refurb much cheaper, or a used part.

If this does fix the problem you'll need to keep an eye on your battery, if it's been consistently overcharged it could develop leaks and cracks, which are bad things.

  • Sounds possible, would it explain the unexpected 0.4 volt circuit? – user568458 May 11 '17 at 9:55
  • The voltage regulator acts on the charge from the alternator, so it doesn't sound likely, although it could have a strange sort of failure. You may have a short elsewhere in the system. – GdD May 11 '17 at 10:02
  • I tested the voltage while revving the engine, I think after you started writing this answer, and the voltage didn't change, kept a steady 14.7 volts. Looking here it looks like the voltage would increase with revs if it was the voltage regulator that was at fault? Could it be the battery not the voltage regulator? – user568458 May 11 '17 at 10:16
  • I highly doubt it could be the battery. There's more than one failure mode for a voltage regulator, I wouldn't assume that someone else's experience matches your case. – GdD May 11 '17 at 10:50

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