Toyota Repair: Corolla intermittently blows EFI fuse, 2005 corolla xrs, wire bundle

Question
Hi Ted,

I need your expertise.  My wife's 2005 Corolla XRS died on her at a busy intersection and wouldn't start again.  I tried connecting it to my code reader before I towed it home.  The code reader couldn't link with the ECU, but worked fine when I connected it to my 2006 F150.  So I suspected there might be some problem with the ECU.

At home that evening, in the fuse box above the left front fender, I found a blown 15A fuse.  The diagram inside the fuse box cover identifies it as the EFI fuse.  I replaced it and was surprised that it didn't immediately blow when I turned the key on.  I connected my code reader; this time it linked, but found zero codes.  I started the engine.  It ran fine with no MIL.  I put a spare fuse in my pocket and took it for a drive.  It only made it two blocks before it died.  It died as I was letting off the clutch and accelerating lightly from a stop.  Perhaps coincidentally, that's what my wife was doing when it failed her.  I replaced the fuse and drove it back home.

I looked around and under the engine for any obvious shorts, like a wire with worn insulation.  The battery had leaked a little from its caps.  I removed it and cleaned up the terminals.  When I saw the bundle of wires running from the fuse box, alongside the battery, toward the engine, I suspected that maybe battery acid had leaked onto the wire bundle.  I tore all the tape off and check each wire for insulation damage.  There was no evidence that any acid had made its way into the wire bundle, so I re-taped it and reinstalled the battery.  I inspected the upstream and downstream oxygen sensor wires carefully - they look fine and don't have any opportunity to rub against anything.

I decided I don't have the time or skills to troubleshoot this problem.  So the next day I took it to a local shop.  I was surprised that it drove the 1-2 miles to the shop with no problems.  I authorized the shop to spend one hour diagnosing the problem I described and to call me if they needed more than one shop hour.  After I called them a couple times a day for three days, they finally called me back with discouraging news.  They couldn't make the problem recur or find any reason that it occurred twice in one day when we were driving it.  They said that since the EFI circuit powers the ECU, they'd need up to 16 hrs to check all the sensors, components and wires associated with the ECU.  They said they'd called the dealership for advice too.  The dealership told them that it might be the ECU itself because apparently Corollas are prone to ECU failure.

I'm reluctant to start playing the part replacement guessing game, especially since these guys want to start with the most expensive part.  I know these intermittently occurring electrical problems can be a real nightmare to diagnose, but there must be a more systematic method of troubleshooting this than just buying an $800 ECU and crossing my fingers as I send my wife an kids out in the summer heat.

This XRS has 107k miles and I bought it new in 2004.  The only repairs performed were replacing the alternator and water pump under extended warranty at about 50k miles.  We live in the desert southwest, so it gets lots of exposure to extreme heat and dust.  Any advice you might offer will be greatly appreciated.  If you can guide me through a reasonable troubleshooting process, I'm handy enough to test circuits, replace parts, etc.

Many thanks,
D.

Answer
Hello, there are known problems with the computers on Corollas from 2005 to 3007 models, although i have not seen any cause the fuse to blow I have seen pleanty of other problems being caused by the ECM, Toyota first issued a service bulletin around 2006 and now it has turned into a recall, which would mean there is no mileage or time limit and if the VIN# and the computer part number are on the recall list you will get the computer replaced at no charge, the reason your scanner did not communicate is one of the symptoms, another is that when the EFI fuse blows the menory in the computer is lost and the codes erased, I would check with the Toyota dealer to see if it falls within the recall, by the way the recall is AOJ special service campaing, good luck.