Catastrophic Electronic failure

[anarchistchiken]

I was driving my car saturday night, everything was working fine, I turned on the windshield wipers and they flew across the windshield, much faster than usual. I hit the rear, it went up and on the way back, the motor slung the blade off the window and it got stuck behind the car. I decided to pull over, hit my turn signal, and it started blinking in a completely erratic pattern, at the same time I noticed that the tach was jumping from 3,000 down to 1900-2300, again very eratically and quickly moving.

The car was running perfectly well at this point, so I decided to continue to my friends house since he is a mechanic who may have some insight. I pulled up and shut off the ignition, and everything died. Every electronic system in the car is now completely inoperable, form the door locks to the odometer. The only working system is the headlights, taillights, and dashboard backlight. The battery has 12.4 volts, all main fuses are in good condition, AND THE HEADLIGHTS WORK PERFECTLY so I'm losing my mind a little bit. If you have any ideas please help.

 

[anarchistchiken]

Heeeelp!

 

[StormTrooper6]

This happened to me once at the car wash, i believe its because the battery got wet and just shorted out for a second, and judging by you having your wipers on, i'd guess the same thing. After i got it jumped, i just ran up to the dealership and it showed that it was working fine.

 

[anarchistchiken]

I can't jump the battery off, its making 12.4 volts. I hoped it was just water somewhere, but i'ts been 3 days and it hasn't magically started working.

 

[pasadena_commut]

Every electronic system in the car is now completely inoperable, form the door locks to the odometer. The only working system is the headlights, taillights, and dashboard backlight. The battery has 12.4 volts, all main fuses are in good condition, AND THE HEADLIGHTS WORK PERFECTLY so I'm losing my mind a little bit. If you have any ideas please help.

Never mind the "main fuses", check ALL the fuses. And don't just look at them, get a voltmeter and measure the resistance across them. By far the most likely thing is that one or more of them are blown, and without working through the whole circuit diagram it is hard to say what that would do. For instance, does the interior dome light or any of the map lights work? Those are just light bulbs controlled by switches, and if they are not working would be a good place to work back from to figure out where the voltage isn't getting through from the battery.

Anybody know if the rear wiper motor works off straight DC? If so, and it went ballistic like that, it could only mean that the DC voltage running through the car at the time was way above normal. That would be bad.

 

[anarchistchiken]

Never mind the "main fuses", check ALL the fuses. And don't just look at them, get a voltmeter and measure the resistance across them. By far the most likely thing is that one or more of them are blown, and without working through the whole circuit diagram it is hard to say what that would do. For instance, does the interior dome light or any of the map lights work? Those are just light bulbs controlled by switches, and if they are not working would be a good place to work back from to figure out where the voltage isn't getting through from the battery.

Anybody know if the rear wiper motor works off straight DC? If so, and it went ballistic like that, it could only mean that the DC voltage running through the car at the time was way above normal. That would be bad.

I'm going to go through all the fuses with a voltmeter when I get home, but I pulled all of them initially and none of them looked blown.

Once I get the voltmeter on in-car systems I'll know more I'm sure, but right now the ONLY path of electricity that is not cut off is the head/tail/dash light circuit. If it weren't for the headlights working, it would be like the battery was removed.

 

[rooster]

test the battery.

not just voltage but pay attention to polarity. halogens will work if polarity is switched but nothing else will.

 

[P-Funk!]

The ECU is the voltage regulator. Can you swap the ECU with another?
Check battery cables for corrosion and chafing (worn/touching metal).

 

[pasadena_commut]

halogens will work if polarity is switched but nothing else will.

Any incandescent bulb will too: the dome light, map lights, cargo area light, and so forth.

Pretty unlikely that while driving along the battery switched polarity, let alone that happens and the car keeps running!

 

[carter1551]

The ECU is the voltage regulator. Can you swap the ECU with another?
Check battery cables for corrosion and chafing (worn/touching metal).

the voltage regulator is built onto the alternator i believe

 

[P-Funk!]

^Double check that. For most cars it is - but for ours it is the ECU.

 

[i12drivemyMP5]

the voltage regulator is built onto the alternator i believe

I'm also gonna go with this. When replacing the alternator, it was listed as listed as internal regulated which is why I assumed it to be part of the reason the MF costs 170.00 & that wasn't a Mazda dealer one either................Not sure what OP car issue is, hoping mine never pulls this. Keep us posted on resolution tho, please.

 

[anarchistchiken]

Only the headlights work, nothing else, no dome, no map lights, no little button lights for AC, radio, windows switch, anything.

Anyone have an ECU I can borrow?

 

[wildo]

Think about this from a logical perspective-

No, the battery didn't "reverse polarity" while the car was running. And a blown fuse removes power to devices- it doesn't make the device run faster FFS.

Most major electrical systems in cars are nothing more than a basic complete circuits, ie a voltage source, user, and conductors. If your wipers were going in super-fast motion, then a logical explanation would be that they were getting more voltage than normal. To me, this would point to a voltage regulation problem. Since a lot of 12V electrics (note, I didn't say electronics) can operate within fairly wide tolerances (not totally unfeasible to consider a 12V headlight running at 12V > x > ~24V) that would also explain why your lights continued to work.

There is also a lot of electronics in the car, must of which I would think are not regulated- there really isn't a need to be. So if a voltage surge were to hit them, I think it is feasible they could be fried. Fuses don't protect against voltage surges, they protect against current spikes. Increasing the voltage to an electronic component would generally reduce the current the component is using (Ohm's law). Though I don't know for certain, I think it is feasible to assume the ECU has a voltage regulator. It's probably running 5V logic internally.

Anyway- my guess is in the alternator (voltage regulator). If it went in a catastrophic way, perhaps it also took out the battery too, which may explain why other systems aren't working after-the-fact.

 

[anarchistchiken]

Batteries holding ~12 volts, checkin it every day, hasn't died yet. That would make the most sense of anything I've heard, the headlights still work, the ECU would have been fried which would explain no ignition and most of the other symptoms. I'll pull it tonight and get it tested.

 

[Focus]

The ECU is the voltage regulator. Can you swap the ECU with another?
Check battery cables for corrosion and chafing (worn/touching metal).

the voltage regulator is built onto the alternator i believe

The ECU controls the field of the alternator which in turn controls the voltage output. The regulator per say is in the Alternator...

Think about this from a logical perspective-

No, the battery didn't "reverse polarity" while the car was running. And a blown fuse removes power to devices- it doesn't make the device run faster FFS.

Most major electrical systems in cars are nothing more than a basic complete circuits, ie a voltage source, user, and conductors. If your wipers were going in super-fast motion, then a logical explanation would be that they were getting more voltage than normal. To me, this would point to a voltage regulation problem. Since a lot of 12V electrics (note, I didn't say electronics) can operate within fairly wide tolerances (not totally unfeasible to consider a 12V headlight running at 12V > x > ~24V) that would also explain why your lights continued to work.

There is also a lot of electronics in the car, must of which I would think are not regulated- there really isn't a need to be. So if a voltage surge were to hit them, I think it is feasible they could be fried. Fuses don't protect against voltage surges, they protect against current spikes. Increasing the voltage to an electronic component would generally reduce the current the component is using (Ohm's law). Though I don't know for certain, I think it is feasible to assume the ECU has a voltage regulator. It's probably running 5V logic internally.

Anyway- my guess is in the alternator (voltage regulator). If it went in a catastrophic way, perhaps it also took out the battery too, which may explain why other systems aren't working after-the-fact.

Kudos to you my friend. It could not have been said better.

Yes, you are correct in saying that the ECU is regulated for voltage spikes, Inverse voltages, etc... The dash however is mostly not, so it may be possible that the dash is fried.

Batteries holding ~12 volts, checkin it every day, hasn't died yet. That would make the most sense of anything I've heard, the headlights still work, the ECU would have been fried which would explain no ignition and most of the other symptoms. I'll pull it tonight and get it tested.

The battery will continue to read 12 Volts, as it's physically constructed that way.

What you need to do, is take out the alternator and have it bench tested for output. From what you are describing it most certainly is putting out way over 16 Volts and that would be the cause of your problems.

 

[wildo]

Kudos to you my friend. It could not have been said better.

Thanks!

Yes, you are correct in saying that the ECU is regulated for voltage spikes, Inverse voltages, etc... The dash however is mostly not, so it may be possible that the dash is fried.

What you need to do, is take out the alternator and have it bench tested for output. From what you are describing it most certainly is putting out way over 16 Volts and that would be the cause of your problems.

You have nicely summed up the points I was trying to get across. Kudos to you!

 

[pasadena_commut]

The ECU controls the field of the alternator which in turn controls the voltage output. The regulator per say is in the Alternator...

Ideally yes. However there is some wire between the voltage regulator in the ECU and the alternator, and I can't help wondering if there might not have been a short somewhere along this path, probably due to water (hence the use of the wipers). At the very least that might have fried the ECU by attaching the wire that is supposed to go to the field coil straight to ground. It's also possible the short went in and out, putting an AC component on the car's voltage, which could make the motors do funny things.

None of this would have blown the dome or map lights though. Presumably they were not even on, and those are simple circuits. A blown ECU will not normally disable a dome light, but I suppose it might if there is a fader circuit in the P5 (don't recall). The map light and cargo space light are just simple wire and switch circuits, right? If those aren't working, the ECU is not at fault.

Go back to square one. The OP sees a voltage across the battery. Apply a small load and confirm that the voltage holds (the headlights will do). Verify that the battery ground is sound. Verify that a test bulb (map bulb, cargo bulb) is not open or shorted. Work from there.

Do NOT plug another ECU in until it is verified the problem does not still exist in the rest of the wiring, else it may blow the replacement ECU.