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I've been ignoring the check engine light on my 2001 Prius for awhile, because I've had to pay too much too often for not screwing my gas cap on tightly enough, and assumed that was the problem again. But, the news is far more ominous. Though the car works perfectly, the dealer tells me that I need a new computer, which runs over $2700. I've got 106,000 miles on my darling car, and haven't had to spend much beyond many tires and basic maintenance, so maybe I shouldn't be so stunned, but I am. I was aware that I might have to cough up for a new battery at some point, but hadn't planned on this. Any counsel? Since I'm not seeing any trouble so far, can I keep driving for a few more days, weeks, months? What do I have to watch out for? The mechanic says one day it just won't start. Has anyone have this problem? Money might be easier to come by in a few months, so I'd sure like to wait, but don't want to be stranded somewhere away from home.
 

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My attempt here might be kind of "Weak" but........you might also investigate trying to get one from a salvaged 2001 Prius?
 

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Computers don't work that way. They don't degrade, they usually either work or fail utterly. Warning that it mail "fail soon" is just not reasonable. I'd get a second opinion on that.

Also, what often fails is the simple stuf: wires, connector pins, sensors. I'd suspect thosebefore an "aging computer."
 

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It would really help to know what codes the dealer found. Can you talk them into telling you? Or can you find someone nearby with a "miniscanner" that can pull the codes? You might check on a few of the Yahoo! Prius groups for people in your area that got the miniscanner.

Chances are that you'll have to ultimately replace the computer to keep the check engine light from coming back. But at least one of the possible problems only shows up on a cold morning start, so you might be able to hold off until next winter if that's the problem.

If you get the codes from your dealer or another owner, post them here and someone will tell you what they mean.
 

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KTPhil said:
Computers don't work that way. They don't degrade, they usually either work or fail utterly. Warning that it mail "fail soon" is just not reasonable. I'd get a second opinion on that.

Also, what often fails is the simple stuf: wires, connector pins, sensors. I'd suspect thosebefore an "aging computer."
You're right about wires, connectors, and sensors going bad first, but there are exceptions.

S.M.A.R.T circuitry on hard drives provides early warning of impending failure. Likewise, many Intel, AMD, and Motorola processor and memory chips have fault-sensing mechanisms.

And car computers can sometimes degrade over time and eventually fail. I had to replace the computer on my 1983 Trans Am around 1991 or so. And its failure was a gradual thing. Sputtering, not driving at highway speeds, etcetera. At first, it only happened once. After a short rest, the car ran fine. Until it happened again two weeks later. Then again in two weeks. And it gradually started happening more and more often until it was almost every day. All throughout this, I replaced all the usual stuff first, plugs, plug wires, O2 sensor, MAP sensor, air cleaners, and so on.

Eventually, the only thing left to replace was the computer/ECU. That weekend, that was the only thing I replaced, and the problems completely went away. I drove the car for another three years without a similar incident.

Gradual weardown is sometimes plausible. Think about it, a computer is typically in the passenger/firewall area of the passenger compartment, where it is subjected to freezing cold in the winter and blazing heat in the summer. Then you start the car, climatize it, and drive...only to shut it down and let it de-climatize until you drive it again.

Alternately freezing and cooking electronic components while powering and/or unpowering them will eventually wear them down.

That's probably not Eric's problem here, but I thought I'd mention it.
 

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Don't over-react to a "check engine" light. Our 2001 Passat has had this warning light showing for most of its life. The garage has periodically reset it, but it comes on again a few weeks later. No significant fault has ever been detected, and we have driven 60000 km in five countries without the slightest concern.

There are many things that can trigger such a warning - including loose connections and malfunctioning sensors - and most of them aren't that important.

The first step is to have the light reset and then to wait and see.
 

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Time and temperature are the primary killer of automotive electronics. Capacitors generally go first and result in highly variable symptoms, generally not a complete failure.

With over 100k miles, I would suggest using a name brand fuel injection cleaner added to each tank of gas for the next 3 or 4 tanks. It is very possible, actually likely, that your issue is a result of a partially plugged fuel injector or other combustion chamber deposits affecting one or more cylinders. Also, if you have never changed the fuel filter, now is the time. Often obstructed flow results in low fuel pressure and thus lean mixtures. This would trigger the check engine light also.

This may not solve your problem, but there is a good chance it will.
 

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mdacmeis said:
...With over 100k miles, I would suggest using a name brand fuel injection cleaner added to each tank of gas for the next 3 or 4 tanks....
And get out and kick the left front tire, too. Hyperion swears by that cure! That, and putting one's right foot in the glove box while baying at the full moon, or something similar. :)

We're so helpful, aren't we? :D
 

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The primary use of capacitors in a digital computer would be for power conditioning, and on memory lines. In those casees, the failures would probably not store codes and set the check engine lamp, but would instead cause general failures such as parity or I/O. I am still doubtful the computer is the root cause of this problem.

Often replacing an ECU solves the problem, because it also replaced or reseated connectors, or repositioned wires broken internally to a contact configuration. The faulty conclusion is that the ECU was the problem. It's fixed, and the customer can't know any better, so the work usually ends there. But a lot of money got wasted.

Ask what codes are stored, clear them, see which ones come back.
 

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mdacmeis said:
. . .Also, if you have never changed the fuel filter, now is the time. Often obstructed flow results in low fuel pressure and thus lean mixtures. This would trigger the check engine light also.

This may not solve your problem, but there is a good chance it will.
But get an estimate on the cost first. My understanding is that the fuel filter is inside the gas tank, so I think you need to replace the tank. Anyway, that's how it is for the 2001-03 model.
 

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Reseating the chips

Temperature changes can cause chips and connectors to expand and contract over time, causing poor connections. You would be surprised how many times a (home PC) computer can be fixed by disconnecting and reconnecting all the connectors, and re-seating all the removable chips (taking them out and putting them back in, or, even just pressing them firmly back into their sockets). This was more common in older systems. The old Atari ST/Mega ST computers were so famous for this that, for quite a long while, Atari was telling owners to disconnect all the cables, pick the unit up about 2 inches, and drop it. The jolt would reseat the chips. It worked like a charm (although I declined to do this - I took them apart and re-seated the chips correctly). I wouldn't be at all surprised to see this same type of issue at work in automotive computers because the temperature changes are much more dramatic. It wouldn't hurt to try to have the unit "fixed" before replacing it. Just pick up your Prius and drop it a couple inches! :)
 

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An IBM repairman told me that they have a name for this "bang on it" process, often used to unstick disk drive motors that have stalled. It's called "Impact Remediation."

Applied to my kids, I referred to it as "Kinetic Instruction."
;-)
 

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'puter...

...or percusive maintenance. It's fixed more than the toaster at our house!
 

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Consider that the ECUs receive some fairly sensitive inputs via
their connectors -- that's one reason there are a lot of shielded
wires running out to sensors here and there. Connectors that have
been in one position for a couple of years over many thermal
cycles can definitely start to change their resistance, and sometimes
grow a small pit between pin and socket which completely breaks
contact. So before blaming an ECU for problems, especially since
ECU failure would very likely be *complete* failure, try reseating
connectors both at the ECU and all over as many places in the
engine and related sensors as you can find. Including
those oxygen sensors buried way down where they're hard
to get at. You might be pleasantly surprised.
_
SMART disk-drive degredation sensing is not a valid analogy -- it's a small
computer reporting on slow degredation of a MECHANICAL device. The little
computer in the disk drive itself is fine, since it's still able to report
on what's going on out there in the HDA.
_
On the other hand, if the ECU itself is beginning to develop cold solder joints and
lifted surface-mount pins, that could also subtly change things in a way that looks like
"computer failure". Effectively the same problem, though, and if you're a brave soul you
could probably pull it out and do a little touch-up with a fine soldering iron. This
technique often works to restore functionality to old video monitors,
which run their components fairly hot and often cook their own pins dry to
the point of disconnection.
_
_H*
 

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KTPhil said:
The primary use of capacitors in a digital computer would be for power conditioning, and on memory lines. In those casees, the failures would probably not store codes and set the check engine lamp, but would instead cause general failures such as parity or I/O. I am still doubtful the computer is the root cause of this problem.

Often replacing an ECU solves the problem, because it also replaced or reseated connectors, or repositioned wires broken internally to a contact configuration. The faulty conclusion is that the ECU was the problem. It's fixed, and the customer can't know any better, so the work usually ends there. But a lot of money got wasted.

Ask what codes are stored, clear them, see which ones come back.
Ummmm....not exactly. In automotive electronics we use RC circuitry to filter and voltage divide signals. Sure we condition power supply signals, but we also protect chips from transients that will result in conversion errors. Analog signals are filtered before being digitally converted. A bad capacitor results in signal swings that look like intermittent failures. We also divide/reduce voltages. RC, LC, and RLC circuitry is also used for electromagnetic compatibility. Trust me - we have more issues with capacitors than anything else and design our products to the weakest link - generally capacitors. Also, the parity and I/O errors you indicate are caught by diagnostics using both integrity checks and dynamic memory checks run during bootup and continuously thereafter. Any cause which results in the microprocessor seeing out of range or invalid data, improperly calculating data, or which results in the micro not running code in a specific sequence within a specific time results in diagnostic codes and fault lamps. We are very careful about ensuring proper, intended operation when it comes to things like air bags, chassis controls, and powertrain controls. If it is running, it must be running correctly.

As for the connector comment - right on! More than half of all automotive customer complaints are related to connectors and terminals/contacts. Whether it is a bad connection (poor contact tension or poor burnish), corrosion of the terminals, mismated connectors, or high resistance from other causes, breaking and then remaking the connection several times fixes more things than anything else. Why? Most automotive computer signals are very low current and most are further DC. As a result, there is limited arcing capability and thus any terminal resistance cannot be jumped. A digital signal is at the mercy of the resistance of the terminals where they make contact.
 

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DanMan32 said:
We? Are you a Toyota engineer? Not trying to be snide, just curious about your background.
No, I do not work for Toyota. But I do work for a company that supplies automotive electronics to many of the auto manufacturers, including Toyota.
 

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DanMan32 said:
Do you have the specs on BEAN and AVC?
Good question! Unfortunately, I am too far removed from that area in my current assignment. However, I know a few people to ask.....
 

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"Most automotive computer signals are very low current and most are further DC. As a result, there is limited arcing capability and thus any terminal resistance cannot be jumped. A digital signal is at the mercy of the resistance of the terminals where they make contact."

Interestingly, this was the very problem the brake light switch recall also had to fix. Outgassing from the seats (not sure if it was covers or padding) built up a coating on the switch contacts. Given the low current drain of the LED brake lights, it didn't get cleaned off in normal use.
 
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