Should capacitors on old ECM be replaced?

[Dave9]

if equipment containing electrolytic capacitors, typically found in its power supply, is used often the capacitors will not dry out and fail. If they do go dry, they can be "reformed" using a Variac.

You are confusing two different failure modes. Electrolytic capacitors can dry out over time and fail, but this does not happen from lack of use, happens either way, somewhat faster if it sees a lot of thermal cycles or perpetual high heat.

Instead, lack of use for long periods (years at a time) with aluminum electrolytic caps causes a breakdown of the oxide layer on the aluminum foil and they become electrically leaky. This can cause rapid overheating and failure, and a lesser temporary concern is a capacitance drop.

It is this oxide layer that you'd restore by applying a low voltage over time with a variac lower voltage supply, but that will not recover a capacitor that is too dried out.

 

[willbur]

You are confusing two different failure modes. Electrolytic capacitors can dry out over time and fail, but this does not happen from lack of use, happens either way, somewhat faster if it sees a lot of thermal cycles or perpetual high heat.

Instead, lack of use for long periods (years at a time) with aluminum electrolytic caps causes a breakdown of the oxide layer on the aluminum foil and they become electrically leaky. This can cause rapid overheating and failure, and a lesser temporary concern is a capacitance drop.

It is this oxide layer that you'd restore by applying a low voltage over time with a variac lower voltage supply, but that will not recover a capacitor that is too dried out.

I somewhat agree- lack of use still does this. you're right about the oxide layer but passing current by use keeps the oxide layer useable. Either way, use keeps the cap useable, disuse does not
Thanks for looking it up on AI

 

[nobb]

If they are potted with an epoxy, then I would say don't touch it and wait until they actually become a problem since you risk damaging the traces when trying to replace. In this case it might even be worthwhile to get a spare ECU and attempt to recap that.

IMO if you get a spare ECU, the caps are going to be of similar age anyways so treat it as a practice board. Also, keeping it in storage unpowered for too long (decades)...may damage the caps in a manner that would require reforming.

In a modern car with a ton of electronics everywhere including the integrated infotainment, I cant even imagine how people will attempt to service these parts in the future.

 

[Snagglefoot]

Rock Auto sells remanufactured ECUs from Cardone and BSE for 1991 Toyotas.