Burning smell of electronics, won't start

Last week I was driving our 2001 Prius, and I noticed a mild burning smell. I was in town, it was very faint, and I wasn't even sure it was coming from my car, so I headed for home and figured I'd check again there. Everything seemed fine until, going 60mph on the level highway, the engine died and the dash lights lit up. I was about to turn off the highway and begin descending toward my town, so I made the turn and coasted for the remaining 7 downhill miles until I got home (to avoid a giant towing bill) .

When I got home, I popped the hood and smelled the scent of burning electronics. The smell was strongest over to the right of the hybrid system, but it didn't seem to be coming from the hybrid system. The smell was definitely not as strong to the left side of the hybrid system. I checked the fuse box (fusible link box no. 1) and didn't find any fuses blown.

My dad (an electrical engineer) came over and checked it out. At first he thought a wire may have shorted under the hood, but we looked and couldn't find any melted insulation, char marks, or the like. I jacked the car up and looked from beneath; again, nothing. The smell did linger for a while though, and was quite noticeable even the next day after having the hood shut overnight.

Turning the key to "ACC," this is what happens:

1. Everything powers up as usual, but the hybrid battery (around 50% as I was driving before the failure) does not register a charge on the display (i.e. it appears empty).
2. The gas gauge registers empty (one flashing bar) for 5-10 seconds, then shows the correct reading (just under 50%) for a few seconds, and until it finally just starts flashing full bars (i.e. full bars > no bars > full bars > no bars and so on, alternating every 500ms or so). (Now that several days have passed since the incident [and I've disconnected the aux battery a few times], it skips the correct reading and goes straight from empty to flashing full.)
3. There are no warning lights on other than the check engine light, which has been on for the majority of the car's life.

When you turn the key to "ON," not much changes. The windows work, as do the headlights and dash backlight. When I start the car in maintenance mode, all the systems it checks show "OK." The auxiliary battery voltage and switch monitors work as well. Up on the top panel though, there are no boxes indicating which gear you are in.

When you turn to "IGN," the main screen and clock shut off for ~500ms, then come back. (I think this is normal but can't remember for sure.) The engine makes no noticeable attempt to start though, and the "READY" light stays off.

I've tried plugging in a DTC reader. The devices gets power, but it can't get a signal from the computer. I've checked the reader on another car, and it definitely works.

I checked the plugs mounted on the right side of the hybrid system for shorted wires (diode check between pins), but I didn't find anything. All of the fuses in all the fuse boxes are intact as well.

It seems to me that a computer is messed up somewhere. My dad and I can't locate any ECUs under the hood other than the hybrid system and perhaps a black box on the back of the ABS pump. We pulled out the body ECU (behind the fuse box to the lower left of the steering wheel), but that looked good. We also disconnected the HV battery (following the Toyota guide) and opened up the hybrid ECU (assuming that's the big silver box under the hood). It looked brand new and didn't smell at all. The resistors checked out as well.

We have the wiring diagram off of TIS, and we've looked over it a good deal but can't come to any solid conclusions. I'm thinking I might pull the engine control module and check that for any fried components but, being on the passenger side of the car, it couldn't have been the source of the smell.

Any ideas as to where to look and what to try would be greatly appreciated. This is our main car and we don't have an excess of cash to replace it. I can take any pictures, videos, or readings that might be needed.

Thanks in advance

 

I didn't really smell it inside the car. I think the little I did smell just came through the window. It was definitely much stronger under the hood.

I checked the four fuse boxes (both sides of engine compartment, to left of steering wheel, and on aux battery) and nothing was blown, nor was there any smell. I also checked for signs of burning wires, but I couldn't find anything.

I have the aux battery disconnected now to keep the security system from draining it. Maybe I should keep the HV battery disconnected too (though it's been a week and the car hasn't burst into flames yet).

And thanks, Bob, for mentioning I had incorrectly identified the hybrid ECU. I think I'll pull that out too and take a look.

I subscribed to TIS for 3 days and downloaded all the wiring diagrams. Anything else you think I should have from them?

Thanks a bunch, guys.

 

I ordered a Mini VCI reader yesterday. It should be here by Monday.

I took out the hybrid ECU and ECM as well. Nothing appeared damaged under a visual inspection. No smells.

I'll remove the inverter cover again and check the wires. I just need to get my hands back on large enough torx bits...

Wouldn't the car have burned down by now if the high voltage wires were shorted? Or it would've popped a fuse somewhere... It took a while for whatever it was to melt to the point where the car died, so I'm thinking it wasn't high voltage. (After I first detected a hint of the smell it made it another 10 or so miles before it died.)

Here's a picture of the inverter from the last time I had it open:

Inverter coolant levels are fine, BTW. Changed it within the last four months.

 

I received my Mini VCI yesterday and got the Techstream software working on a spare laptop. I was able to connect to some of the car's computers, but not all. Here's a screenshot:


The EMPS is the only one that shows an error. It says a power supply relay is out, but that's probably just the result of a more general power failure.


In the first image, it shows the immobilizer as having an unknown status. I'm not exactly sure how that differs from "not supported or not responding," but perhaps it means the computer has power but is confused and the DTC reader is able to (partially) connect to it. The immobilizer being confused would explain the engine not starting, but the immobilizer is interior electronics, and the burning smell was in the engine compartment.

There's still more to the problem than the immobilizer being messed up though. The other computers don't seem to be working, which explains the missing HV battery charge on the multi display, gas gauge confusion, and missing outside temperature reading (it says "E").

I tried running a CAN bus check, and it didn't come up with anything. It may have returned an error the first time, but when I tried it again I didn't return anything but a blank table. I could try running it again and post a screenshot if anyone thinks it would be useful.


Apart from computer checks, I also pulled off the inverter cover again and gave the connectors a good sniff. By this time the smell in the engine compartment had gone away, but I may have been able to detect a slight hint of the smell near these connectors. Had this been the same smell, it could have been traveling up the high voltage shielding tubes, in which case the source would've been the transaxle. I measured the resistance across the terminals, and they all measured the same, very low resistance (I can't remember exactly what it was, but I can go measure again if need be).

It is possible that the transaxle was damaged recently. I've taken over servicing this car, and I drained the engine coolant a few months back. But I took out one too many plugs on the bottom, meaning I (**wincing**) accidentally drained the inverter coolant reservoir as well. The car ran fine for a while, but when we tried to climb several thousand feet it went into panic/overheat mode and shut down. When I got home I realized what I'd done and promptly refilled the reservoir. Then the car ran fine for another two-plus months, before this happened while cruising on level ground.

So let's say that my ignorance killed the transaxle. Why did it wipe out so many computers, without (seemingly) taking out anything on the inverter board?

I could potentially salvage a good transaxle from a friend's Prius (dead HV battery), but I just watched a video on YouTube and it looks like it'll be more trouble than it's worth to replace it. I'm hoping it doesn't come to this...

 

I'm also not familiar with the Techstream software, if anyone has any usage tips, they'd be much appreciated.

 

Good news! We got the car working again!

Turns out the inverter coolant pump was bad, and that was what was smoking. It had blown the AM2 fuse, which we hadn't noticed at first (note to self: check all fuses twice before digging deeper and wasting time). We replaced the fuse and saw that the pump was smoking. The local Toyota dealer had the pump in stock, and my dad was able to talk them into selling it to us for $155.

Now the car is running great again (or as well as it can for a car with 200K+ miles on it). The timing belt does need to be replaced though, as it's making noise. I guess that's next on the list...

Thanks so much for all the help, guys! Though I may have wasted a bunch of my time, I did learn a lot.