Why do hybrid battery control module connectors get corroded?

Way back when I had my first car, the rubber-sealed weatherproof connectors now used under the hood were not a thing yet, and terminals were more exposed, and I noticed a pattern to which ones seemed to grow the most malachite (the green stuff). They would be the ones on constant-powered circuits, 12 volts 24/7.

I think malachite and azurite are both compounds of only copper, carbon, oxygen, and hydrogen, so all the needed stuff is there with a copper terminal in humid air, but it must help to have a voltage gradient to grow the stuff.

There are voltages constantly present on those orange-connector wires. They're the same wires at the other ends where they attach to the battery modules, but those ends are spaced out farther apart. The ends in the orange connector have the same voltage differences in a tight group with much smaller distances, so the voltage gradients there are steeper.

 

So I just asked Google AI and then Asked ChatGPT this question and as usual GPT one was better (enclosed below):

Specific to Prius packs there lots of different humidity-based and electrochemical and akaline processes involved that lead to this corrosion from trace amounts of NiMH electrolyte leaking from the seals of the modules. No doubt severe changes in temperatures play a roll in these very tiny leaks that Toyota can't prevent in a cost effective way. But your original voltage sensor wires act a means for the corrosive process to reach the pins of the ECU and you can get a new higher quality voltage harness at a 10% discount if you use this link: http://www.acenbay.com/?ref=priuscamper

If the corrosion on the pins inside the ECU goes on for too long you'll start getting micro-arcs between that first pin and one next to it and you'll see it first as a sudden voltage drop down to one or two bars on your charge screen even though pack hasn't lost charge, it's just the ECU sensor getting scrambled. Once it progresses you'll get smoke and melting of the voltage sensor plug at the ECU which usually destroys the ECU.

Anyways, here's a taste of how this corrosion happens according to chat GPT:



ChatGPT - Electrolyte corrosion process

 

What was the prompt you used to get that ChatGPT response? Did you hint that you wanted electrolyte leakage to be part of the answer?

I've seen malachite dependably grow on copper terminals given just exposure to humid/road environment and constantly-applied voltage.

A lot less of it in modern cars because the sealed, weatherproof connectors used under the hood have become much, much better.

The orange connector in the battery isn't that sealed kind though.

 

The vapourised electrolyte from the modules reacting with oxygen and copper is the major catalyst to promote this sort of corrosion, a bit of heat generated by resistance across a joint helps to speed it up.
The real problem leads back to the pressure relief system in each module. They are supposed to release at around 80psi and vent outside the vehicle through those rubber hoses and joiners that connect every second module.

These rubber bungs get stuck and the internal pressure in the modules climbs enough to force the electrolyte out through the terminal seals.

It will be interesting to see if your voltage sensing harness has corrosion along the length of the wire, two of mine did, so I'm interested to see if this is common or just than my two Priuses had second hand battery installed during their long life, so the corrosion problem is exaggerated in my case.

I know I had to push the terminal pins further through the plug in the battery computer so they made a deeper contact into the pins in the plug ..... this appears to be a common problem resulting in a burnt pin and terminal in the plug, caused by a poor contact and gradual increase in resistance, heating the pin and it retreating further into the computer housing .... heating the pin housing from both sides with a hot air gun, while pushing the pins through, seemed to sort the problem ...... as a test, use a pin or small diameter wire and measure the depth of the socket in the new harness plug, then compare that with the length of the pin sticking out of the computer plug ......

T1 Terry

 

If you have corrosion at ECU most likely the electrolyte has wicked it way up the wiring from the leaking cells. It needs to be replaced so find a good harness to use and cut open the bad one and inspect the entire length im sure you will see corrosion the entire length.

SM-G960U ?

 

Had you clicked the link/reference you would of seen the question asked was: "How does electrolye cause corrosion when it leaks?"

 

VW had an issue with coolant getting to instrument clusters found out the coolant sensors leaked inside sealed connector and coolant was pushed all way to cluster inside wiring insulation so yes it will wick up wiring

SM-G960U ?

 

As I generally browse with JavaScript disabled, clicking the link shows me an approximately blank page. But thanks for clearing up what the prompt was.

I'm largely in favor of including the prompt up front whenever citing an AI result; it's always useful to know what result the AI was asked to produce.

 

It wouldn't take much effort to turn your Java script functions back on for a second rather than make me work for you to answer your question. Likewise, I bet there's all kinds of instances that you're wasting significant time unable to get a question answered that was right in front of you in a matter of seconds had you clicked your java script back on for a second.

Do you still use a landline as your main telephone too?

 

You sound a little like the web sites that patronizingly explain how I can turn JavaScript on, rather than explaining why they designed a site to not show the information I came for unless I allow them to use my computer to run code I haven't vetted.

Including the prompt in the post with the result means no time spent later responding to inquiries about the prompt.

 

Wow, life must be getting tough over there, everyone is at each others throats it seems .....

As a 40 yr plus mechanic, I have seen some really strange things, like wiring harnesses with an oil leak, even oil appearing at the instrument cluster in a VW Kombi ..... the engine is in the back so a long way for the oil to travel ..... but it did, the previous genius had sealed the wiring boot on the oil pressure switch to both the switch and the wiring ... stopping to oil leak at the engine The fix in that case was an oil catch rag in a plastic bag under the dash, and replaced the oil pressure switch with another oil catch rag at that end and told the owner to change it weekly until it slowed down, then, as required.

The way the copper conductors are twisted in the harness, they carry any liquid or vapour along the length of the cable, no matter how long it is ..... one of those mysteries of life as to why .....

T1 Terry

 

In this particular case the answer to your question was in Java script and when it comes to sites that don't show needed information without JavaScript enabled, you're basically saying that smart phones and the use of phone apps are not worthy of your ridiculously high standards.

In other words what you're really saying is:

 

I certainly understand the difference between a web site that displays, say, data visualizations or tables derived from some kind of data store or anything else that intrinsically calls for some kind of client-side logic, and a site that I'm going to just to see some piece of static information identified by its URL. The sites of the former kind that I've decided are worth using, my JS-block extension already knows about.

My ridiculously high standard doesn't take a lot of words: my computers have been bought with my money to run software installed by my choice or written myself, not software that some webdev grabbed off the internet for a site I casually visit once. Naturally I make exceptions for sites that need them, if I need the sites.

If I install an app on my phone, that's software installed by my choice. And no, I don't click "Install the app!" on every web page that offers an app.

In some ways it saves me a lot of time. Twitter (I guess it's X now) I've never been on, but I used to read occasional tweets that were in the news or forwarded to me or what not. That was back when the site would detect no-JS and send you to a "legacy" html page that just showed the tweet.

Then some years ago they dropped that, and I haven't read a tweet since. Ahhhhhh.....

 

As somone who spent all of the 90's never having enough banwidth to view more than just text on the the internet I can kinda relate, maybe? But I'm never going to be able to write as eloquent of a "get off my lawn" rant as well as you just did.

 

People who conflate an attempt to elucidate by providing background information with a rant. Dear oh dear.

 

Dont forget to use promo code azusa to save at AcenBay.com

 

T1 Terry
"As a 40 yr plus mechanic, I have seen some really strange things, like wiring harnesses with an oil leak,"

35 years here.

As far as the battery ecu corrosion, I suspect that it's mostly ambient dust and humidity mixed in with high voltage potential from the hybrid battery.

I dissected a "bad" voltage sense harness, and didn't see any corrosion inside the wire insulation. Just at the ecu connector.

Posted via the PriusChat mobile app.

 

Thanks for this... I've always been hesitant to say that visible corrosion can travel up the wire into the ECU, but it does play a role, it's just that for reasons I've outlined in AI reference above, there's lots of different factors that lead to that corrosion showing up inside the ECU and I thought they fixed it in Gen3 but in some cases they didn't.