Should I replace the capacitors on my 30 year old car's Electronic Control Unit?

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
I have an old Honda Civic. The main capacitor on the ECU's circuit board are known to fail and leak when they get old. I took out the ECU and luckily there are no signs of leakage yet and the board "looks" very good. I have seen photos showing that when a capacitor fails, it can ruin the circuit board.

Aside from the main capacitor, there are 8 smaller capacitors on the board. I want to keep this car for as many years as possible so I am thinking about having all 9 capacitors replaced.

I know very little about electronics but noticed that the original capacitors are rated at 105 degrees (Centigrade, I think) if that helps.

Would you:

1. Leave well enough alone?
2. Replace just the main capacitor?
3. Replace all capacitors?


If I have posted this in the wrong forum, please let me know and I will try and correct that.

Also, does anyone know a better forum online where I might ask this question?

I really appreciate any help you can offer.
Thank you
 
Last edited:

Ian0

Joined Aug 7, 2020
3,508
How hot is the ECU when the vehicle is running?
I looked up a random 105°C capacitor datasheet.
https://docs.rs-online.com/6b69/0900766b81364135.pdf
It is rated 5000 hours at 105°C, 20000 hours at 85°C and 175000 hours at 50°C
At an average speed of 40mph, 5000 hours is 200,000 miles, and 20,000 hours is 800,000 miles.
So, I'd go for 1) leave well alone.
Actually I'd go for 1+, which would be acquire a spare board, keep somewhere safe (and cool but not damp) and leave well alone.
 

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
Thank you

The ECU is located in the passenger compartment right next to the front passenger right side kickboard. So it is subjected to temperature ranges from about 5 degrees C in the winter and 65 deg C in the summer I live in southern Arizona. I don't know how hot the inside of the ECU gets while it is "live".

However, apparently during the late 80s and early 90s there were some substandard capacitors installed in these Hondas. There are a number of reports of failed and leaking capacitors in the ECUs. There are even kits being sold on eBay to fix the problem. However, I have read that often substandard Chinese capacitors are sold on eBay.
 

dl324

Joined Mar 30, 2015
13,313
My philosophy is to only replace components that are known to be defective. If you don't have an oscilloscope, you can tack good caps across ones that you suspect; assuming a failed cap would be opened. The ones that initially fail shorted usually progress to becoming an open unless they trigger some overcurrent protection.

If you don't know what you're doing (soldering-wise), you could cause more harm than good blindly replacing components.
 

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
Thank you.

You have good advice. If I decide to replace the caps I would have an electronics person do it. I can solder, but well enough to deal with the intricacies of a circuit board.

Right now the car is running fine, so I am guessing that the caps are ok. But I know someone who's similar Honda broke down and it turned out to be a bad ECU cap. In most electronics, I'd follow your advice and wait. But I'd hate to be stranded in a car due to a bad cap.

If only there were some info available as to the percentage of ECUs that have failed then it would be easier to make a decision.
For example, if only 5% of these Honda ECUs have failed, I'd leave well enough alone.

I plan to heed the advice of those on this forum who comment. Hopefully there will be additional input from others and consensus.

I really appreciate the posts thus far.
 

dl324

Joined Mar 30, 2015
13,313
I have never had a problem with bad capacitors in an ECU. I have 4 vehicles that are over 20 years old: a 1990 BMW, 1990 F-150, 2000 Chrysler Town and Country, 2000 BMW.

The only problem I've attributed to bad capacitors was in a 10+ year old DVR. Four in the power supply section and all exhibited bulging.
 

dl324

Joined Mar 30, 2015
13,313
In the link below is an example of the capacitor kit and a photo of a leaking capacitor from an OBD1 Honda ECU
I'd imagine that they like to sell as many caps as they can for $5 each; that's quite a markup.

The cap they say is leaking looks like adhesive to me.
cap.jpg
 

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
Thanks for the comments, keep them coming.

In the photo in post #8 it isn't the yellowish glue. It's the brownish colored part of the circuit board that is "east"-"southeast" of the capacitor. The arrow in the photos is pointed at the capacitor that is "leaking".

Attached is another failed ECU circuit board showing a leaking or burned capacitor. Most people who have these cars aren't electronics experts, such as the folks on this forum. So they describe the caps as leaking. Maybe a better description is burned out. In any case, it doesn't look like glue in this case.

The reason I posted the "online kit" that is for sale wasn't for the pricing. It was to show that failed capacitors are a known issue with the late 80s -early 90s Hondas, to the extent that kits are sold online.

Thanks for your help.
 

Attachments

Last edited:

dl324

Joined Mar 30, 2015
13,313
Now I see the leak. A circle around the leaked electrolyte would have been more informative:
leakingCap.jpg
That cap should definitely be replaced and the electrolyte needs to be cleaned up before it causes things to corrode.

The labels at the 1 o'clock position make me think that they're rated for 85C; not the 105C that they should have been.
 

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
Maybe some of the ECUs were sourced with 85 degree caps while others had 105 degree. If it is the 85 deg caps that are failing, that might explain it.
 
Last edited:

Thread Starter

GlennJKH

Joined Aug 9, 2021
12
Looked at the capacitors more closely and found "KME" marked on them. Looked it up and it could be Chmicon KME capacitors. I found this on the internet at a Honda NSX site, nut sure how accurate it is. "The Chmicon KME capacitors also appear to have only a 1000 hour rating". If true, that would be less than the 5000 hour rating noted in post #2.
 
Top