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Car occasionally goes into electrical coma, then wakes up fine
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holtt
New User
Aug 24, 2012, 9:21 AM
Post #1 of 8
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Car occasionally goes into electrical coma, then wakes up fine
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91 Toyota Previa with about 160k miles on it.
The car runs fine, one of those "the original owner had all the maintenance done" cars that's a joy to own.
Except for one thing.
On rare occasions, I'll go out in the morning to start it, and the sequence goes something like this...
1) Dash lights turn on for a brief amount of time, plus the "seatbelt not yet fastened" chime sounds. Probably 1/4 sec or less.
2) Everything goes dead
3) I try to start it again, and I get nothing. No dash lights, nothing.
4) Remove key & replace - nothing.
5) I can hear a faint buzzing/clicking from under center dash area, which goes on and off intermittently. Sometimes the buzzing lasts for several seconds . This happens even though the key is removed. Same sound if key is in.
6) Eventually after 5 minutes or so, the car stars up just fine
7) After one of these events, the radio and clock are reset as they have completely lost all power.
Any ideas? That last point (everything loses power) is the one that throws me a bit and makes me think of the fuse block on the battery. However the fact that I get this buzzing under the dash when it's in it's coma is a bit odd.
(This post was edited by holtt on Aug 24, 2012, 9:33 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 24, 2012, 9:38 AM
Post #2 of 8
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Re: Car occasionally goes into electrical coma, then wakes up fine
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You have a connection issue somewhere. It could be at the battery or any of the various power connections or even a bad ignition switch. The circuits will have to be troubleshooted to determine at what point the supply is being lost.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 24, 2012, 10:03 AM
Post #3 of 8
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Re: Car occasionally goes into electrical coma, then wakes up fine
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Doesn't this car have a lot of things going on and connections right at battery positive terminal? Take a good look at that as it might be all corroded and perhaps need more than just cleaning up but replacing stuff there. Plain chintz clamps are not very corrosion tolerant. If so and you think that can be cleaned up with some wire brushing go for it and use an electric friendly grease.
Negative off first (clean it too) and back on last. If any alarms, radio codes etc., make sure you have the procedure to reset those or use a memory saver,
T
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holtt
New User
Aug 26, 2012, 1:36 PM
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Re: Car occasionally goes into electrical coma, then wakes up fine
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Did it again big time on Friday, this time the chattering never stopped in the relays under the dash, and managed to drain the battery pretty deeply. This was with the key out.
After a jump it decided to run so I got it home from work & in the driveway.
This morning I tried starting it again, same deal. This time I popped off the cover to access the relays and such, and could identify just which one was buzzing. Pulling it caused several others to buzz. Again, this was all with the key OUT after trying to start it.
Right now I'm wondering if it's not just the ignition switch, given the fact I get relay buzz with the key OUT and switch OFF. If the ignition switch contacts were dirty or incomplete I'd get weak power and no full relay contact. And if they were sticking part way on on sometimes I'd get the relays chattering even with the key out.
If it was say, a loose, corroded or bad connection off the battery or near the battery, that doesn't fit with the fact that the relays chatter with the key off. The chatter with key off means it's still getting electricity even if the switch is off.
Is there a way to bypass that switch temporarily (short out wires) to see if it is the cause?
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Hammer Time
Ultimate Carjunky
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Aug 26, 2012, 2:52 PM
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Re: Car occasionally goes into electrical coma, then wakes up fine
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The car starts with a jump. That makes it very clear that you have a battery issue. Either the battery is no good, a bad connection at the battery or something is draining it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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holtt
New User
Aug 26, 2012, 3:05 PM
Post #6 of 8
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Re: Car occasionally goes into electrical coma, then wakes up fine
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How could a bad battery cause the ignition switch to not fully shut off power to the relays?
I assume the only reason it needed a jump because the relays had been stuck on with the key out for several hours.
(This post was edited by holtt on Aug 26, 2012, 3:07 PM)
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Hammer Time
Ultimate Carjunky
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Aug 26, 2012, 3:11 PM
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Re: Car occasionally goes into electrical coma, then wakes up fine
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Hence, the drain I referred to.
Something not shutting off will drain the battery overnight. the end result is still a dead battery.
There is a procedure for finding a battery draw like that.
You will need a digital ammeter and a jumper wire with clips on the ends to do this.
First rig any door switches so you can have a door open without triggering the interior lights and unplug the hood light. Remove one battery cable and attach the meter in series between the battery cable and battery post. Take the jumper wire and also attach it the same way. Leave the jumper wire on for at least 10 minutes to expire all the automatic timers. Now remove the jumper wire and read the meter. Anything over 50ma is too much draw. The way you locate this is to start removing fuses one at a time until the meter drops to normal level. This will be the circuit with something staying on. Determine what components are part of that circuit and check them individually until the problem is isolated.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Aug 26, 2012, 5:02 PM
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Re: Car occasionally goes into electrical coma, then wakes up fine
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Low voltage to the relays because of a discharged battery or connection problem will cause the relays to chatter. When the voltage gets too low the electromagnets can't hold the relay contacts closed. When in that state the relays chatter because they are in a state of not being able to hold and holding the contacts shut.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Aug 26, 2012, 5:03 PM)
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