Newbie in Need! (Already used "search," don't worry)

Hi Andrew,

Not to worry, there's no big expensive set involved. You can get by with just the front bus wire assembly 8216547030, about $110 at Village Toyota, or for only about $5 more you can get the full replacement parts kit as used in the official battery rebuild campaign, 0400335147, $115 at Metro Toyota, which gives you all the wiring, bus components, protectors, resin end sheets, etc., to make a battery overhaul complete.

I'd strongly recommend against doing anything besides ordering the correct harness. In general it's great that you don't have qualms about soldering, but in this specific case you really ought to. That bunch of skinny wires with thin (but carefully chosen) insulation are bundled very close to each other, with a potential difference that can exceed 300 volts between some of them, and no provision for limiting current. (One of my earliest posts on PriusChat was before I had ever seen this harness in person and I just assumed that they would design it with integral limiting resistors out at the battery terminal ends, but it turns out they didn't!) Hence the one fire you can see you've already had.

The fire seemed to stay contained in the battery enclosure that time, and it sounds like nobody was hurt. But trying to rebuild that harness using anything other than the original materials and construction could be like telling the school bully the first time he hit you didn't hurt bad enough.

-Chap

 

It sounds like you might be describing the second case I've ever heard of where the sense wire harness caught fire near the ECU.

This is starting to make me curious.

You might follow that thread for a sense of some of the complications that cropped up in that repair. It seemed that smoke from a fire incident may coat all of the modules and connections, producing unintended ground paths and a tendency for the modules to self-discharge.

-Chap

 

Also, with that incident so close to the ECU, the ECU itself (connector and circuit board) are probably at least coated with carbon, if not actually melted or burned, in exactly the last place you'd want that kind of damage, around the sense line input / high voltage isolation section of that board. If you don't just replace it with a known good ECU, I'd certainly recommend a very careful inside cleaning and inspection of the one you've got.

-Chap

 

Is there any chance we could see some pictures of the damage?

Avi

 

Pictures!

There is a minimum posting number needed, 5?, but we sure would like to see what you've found.

Bob Wilson

 

Voltage doesn’t cause wires to burn. Current does cause wires to burn but those wires have basically zero current in them unless something rubs through wiring (or similar).

 

The wire gauge by itself isn't a problem because, as valde3 points out, in normal operation those wires carry so close to zero current it's not worth talking about. In a fault situation that puts current through them, yes, the light-gauge wires will heat faster than heavier ones would ... but I would expect arcing right at the fault location to be a much bigger source of heat, at least at first. Damage due to ohmic heating of the wires would probably be spread all along them, but the photo in lovemy02prius's case seemed to show damage very focused near the connector to the ECU.

The voltage doesn't really put any constraints on the wire gauge, but it does put demands on the insulation type and thickness. The insulation on those wires is a lot thinner than the plain PVC insulation on normal 12 volt auto wire, but Toyota obviously spec'd an insulation type that can handle the voltage at their design thickness. To be sure, they didn't drastically overengineer this harness, or they'd have done the belt-and-suspenders thing I assumed they would do, and formed integral, say, 10 MΩ resistances into it right at the terminals that attach to the modules, and then any harness damage would give wacky block voltage readings and some DTCs but no smoke. But I don't think I've seen them underengineer stuff either. I'm sure they put plenty of attention into approving their insulation choice and construction and quality control, and honestly this is only the second post I've seen on PriusChat with an issue like this. They certainly would not build the harness in a way they expected to fail.

Most likely, something had to first create an insulation flaw near that connector. Maybe an unlucky beetle crawling over that connector, then some of the insulation getting sprayed off by superheated beetle cytoplasm? Whatever it was, as soon as anything starts there, it's no surprise what happens next. The mystery is just how it starts.

In your case, you mention first noticing the damage the second time you were in the battery, after doing some earlier work and putting it back in the car. You haven't said whether you thought the damage could have been there already, but I'm guessing if you were doing such close work as cleaning all the terminals, you would have noticed it. So it seems possible the failure happened after your first reassembly.

In lovemy02prius's case, there had also been some work done on the battery. We might not know exactly what because she bought the car used, but the battery innards were not all original so someone had clearly been in there.

I wonder whether there might be handling precautions we need to learn for working around that harness. Avoid rough handling? Gloves to avoid salt sweat tracks on it? Is it possible that, for safety's sake, that's just a harness that ought to be replaced as a matter of course when overhauling an old battery?

Looking forward to the pics of yours....

-Chap

 

I understand the ECU uses a sampling cap that is then switched to the ADC. I am going over my mind what sort of short might lead to sense wire overload.

If the sense wires were on either side of the safety jumper and the car off, critter bodies could do it to the case. I don't see electrolyte trace leaks with enough current as it would hydrolize and or steam off the water.

Still, check the air ducts for spider webs.

Also blow off any dust in the electronics area in case it is conductive.

Bob Wilson

 

Or really the third - I had forgotten about Russell Walker's in Brisbane in 2013.

List of similar incidents I know about here.

-Chap