This is a quick note for people who might be googling for some advice as they try to work out why the battery in their Toyota Previa is dying. We’ve just had that very problem with our Previa (ours is a 2005 model, which is the version that Toyota introduced in 2002 , and is also probably very similar to the similar shaped 2000 model before it).
The symptoms were that the car would not start because of a dead battery after it had been left over night (or for a few nights). The battery would be fine when the car was parked (i.e., you could easily restart it 10 minutes after a run), but the next morning it’d be dead.
I started out trying to diagnose it myself (though with hindsight, I should have probably taken it straight to the auto-electrician). Obviously we’d checked all of the lights, switches and whatnot, trying to find something left on that might be causing the problem. I also removed the radio. Eventually, I disconnected the negative terminal lead from the battery and measured 100mA between the battery and the loose ground cable. I didn’t fancy isolating it to a circuit (by removing fuses and relays), because it would have been a pain to do with my standard multi-meter (holding it on the battery required two hands just for that) and there was no guarantee that I’d know what to do anyway, once I’d isolated it.
So I took it to an auto-electrician. He measured the actual draw as closer to 1A (shows how well my cheap multi-meter works!) and after a few hours labour, he had tracked it down to damp wires in the loom at the back of the engine bay. He replaced the affected wires, sprayed it all with silicon spray and replaced the battery (which had suffered from going flat so often in the sub-zero temperatures we’ve had lately). It’s working fine for now, and fingers crossed it’ll be fine for the rest of the time we have the car. I do wonder if it’s a weakness in this particular car though.
Anyway, if you’re having a similar problem with your Toyota Previa, take heart. I’d definitely recommend you take it to an auto-electrician. By all means, tell them what you’ve read here, but they’ll probably want to diagnose it themselves anyway, because there are other problems that can affect batteries in this way (like dead diodes between the starter and the battery).