Should capacitors on old ECM be replaced?

[Kurtatron]

I’ve read time and time again that capacitors don’t last forever, but I’ve never witnessed capacitors fail on vehicle ECMs. I have a 1991 Toyota ECM. The capacitors are not bulging.

But I’ve seen damage caused by a burst capacitor. Looks like it can take out an entire board.

I guess my thoughts are, maybe the capacitors on these old 90s electronics are so good, that they should not be replaced. Maybe the quality was so good that replacement capacitors are greater liabilities.

has anyone ever replaced the capacitors on an engine ECM? Or do the OEM capacitors just never seem to fail? I mean, the internet says capacitor lifespan is 10-15 years, but mine are 37 years old and show no signs of failure.

 

[JohnnyG]

I'd say that kind of preventive maintenance would be way beyond most people's capabilities. There is also the possibility that the capacitors in the ECM are "potted" with an epoxy sealant that would prevent access.
It might be a better idea to find a complete known good ECM for a spare. If you'd like to proceed with your plan, I understand that Tantalum Capacitors have the best longevity.
They also come with their own set of requirements that might be difficult to comply with. Such as they should be rated at twice the expected voltage for the best longevity, polarity must be strictly followed, etc.

 

[Nukeman7]

I've not encountered that problem on Toyotas; however, leaking capacitors were notorious on Honda ECUs and TCUs in the 1990's. Allegedly, many of the Honda ECUs/TCUs had counterfeit capacitors that were made of inferior materials in the overseas black market factories. I've repaired three Honda units when they failed several years ago.

In your situation, I would follow JohnnyG's advice and locate a spare ECM for your Toyota. If you choose to attempt a cap replacement, I suggest sourcing the proper capacitance value(s), but upgrade to a 25 voltage rating instead of a standard 10 or 16 volt rated capacitor. It will be slightly larger but have more heat dissipation ability and longer lifespan. Reputable brands include Nichicon and Panasonic.

 

[martinq]

I’ve read time and time again that capacitors don’t last forever, but I’ve never witnessed capacitors fail on vehicle ECMs. I have a 1991 Toyota ECM. The capacitors are not bulging.

But I’ve seen damage caused by a burst capacitor. Looks like it can take out an entire board.

I guess my thoughts are, maybe the capacitors on these old 90s electronics are so good, that they should not be replaced. Maybe the quality was so good that replacement capacitors are greater liabilities.

has anyone ever replaced the capacitors on an engine ECM? Or do the OEM capacitors just never seem to fail? I mean, the internet says capacitor lifespan is 10-15 years, but mine are 37 years old and show no signs of failure.

Yes, absolutely they can / should be replaced. You can wait for them to wear out or leak and cause damage or you can replace them in advance. Some electronics / ECUs have a trend of capacitor failure after a number of years and those should definitely be addressed ASAP. Others will last many decades and very slowly degrade with very few reports of damage, just performance issues.

I've replaced many capacitors that looked and tested good. If you need to remove them to test them properly you might as well replace them but you MUST replacement with a known good brand / model from a reputable supplier, hopefully not from Amazon / Ebay / Aliexpress, etc. There are plenty of "fake" and poor quality components out there.

Often you can get a good idea of their condition by testing them in the board and inspecting them closely with magnification. I've witnessed many people look at caps and say they "look good" but under close inspection a leak can be found. Not all bad caps leak but all leaky caps are bad.

 

[Lubener]

I have replaced electrolytic capacitors (they do have a shelf life and the ones that go bad ) in the ECU's in both of my old 87 Fords. They will "usually" bulge out or leak when they are bad and ready for replacement. If you are going to check them with a tester, it's best done out of circuit and if you are going through that trouble, might as well replace them.

My advice if you change them, stay with the same capacity and temperature rating but I bump up one step on the voltage rating for added durability.

 

[iCurious]

When you get a bunch of weird or series of codes or the car doesn't start it is a sign.

There are some specialty shops able to run a test but it requires you to disassemble it.

 

[Kurtatron]

Yes, absolutely they can / should be replaced. You can wait for them to wear out or leak and cause damage or you can replace them in advance. Some electronics / ECUs have a trend of capacitor failure after a number of years and those should definitely be addressed ASAP. Others will last many decades and very slowly degrade with very few reports of damage, just performance issues.

I've replaced many capacitors that looked and tested good. If you need to remove them to test them properly you might as well replace them but you MUST replacement with a known good brand / model from a reputable supplier, hopefully not from Amazon / Ebay / Aliexpress, etc. There are plenty of "fake" and poor quality components out there.

Often you can get a good idea of their condition by testing them in the board and inspecting them closely with magnification. I've witnessed many people look at caps and say they "look good" but under close inspection a leak can be found. Not all bad caps leak but all leaky caps are bad.

Checking online, buying capacitors is overwhelming. There’s so many different types. Organic, hybrid polymer. Does it matter what kind of capacitor if the capacitance and voltage is the same?

 

[The_Jeff]

Checking online, buying capacitors is overwhelming. There’s so many different types. Organic, hybrid polymer. Does it matter what kind of capacitor if the capacitance and voltage is the same?

Yes, it's electrolytic that typically fail, so you want electrolytic to replace electrolytic. (They look like little water towers.)

I wouldn't preemptively replace them if there's no trend towards failure and if things are working normally.

I did change them on my bricknose F150 because they're known bad, and mine were visually dribbling goo on the main board surface.

I've also changed caps in 2nd gen Prius dashboards due to a known issue, and I've changed surface-mount resistors in a W-body Buick Century, again, due to known issues getting the odometer to light up.

 

[paulo57509]

Chronic issue with 1st Gen Lexus LS400's. I wouldn't doubt that this is still a concern today with other makes. It's not so much the capacitors themselves causing crazy behavior. It was the caustic salts that damaged the multi-layer PCA's.

https://www.clublexus.com/forums/ls...exus-issues-solved-ecu-leaking-capacitor.html

 

[wlk]

I had my ECU and PSOM rebuilt in my '94 F350. It had corrosion and leaking capacitors and resistors in the ECU causing shifting issues.
I wouldn't just replace them if all is well though. I don't like poking the bear for no reason.

 

[vwmaniaman]

My son had a 1990 F150 that would not start if it was raining and it was an electrolytic and a tantalum that failed. I replaced them and it is still working and that has been at least 7 years ago. My 1990 ranger with the 2.9l failed to start and it had 2 bad electrolytics in its computer board. They do fail but they worked a long time.

 

[Gasbuggy]

I redid them myself in my la400 ecu and gauge cluster... What a fun job

 

[Legs4Arms]

If you've ever owned a Foxbody.

Yes!!!!

 

[willbur]

I’ve read time and time again that capacitors don’t last forever, but I’ve never witnessed capacitors fail on vehicle ECMs. I have a 1991 Toyota ECM. The capacitors are not bulging.

But I’ve seen damage caused by a burst capacitor. Looks like it can take out an entire board.

I guess my thoughts are, maybe the capacitors on these old 90s electronics are so good, that they should not be replaced. Maybe the quality was so good that replacement capacitors are greater liabilities.

has anyone ever replaced the capacitors on an engine ECM? Or do the OEM capacitors just never seem to fail? I mean, the internet says capacitor lifespan is 10-15 years, but mine are 37 years old and show no signs of failure.

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.

 

[Kurtatron]

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.

Then what does cause the leaking? Disuse?

 

[willbur]

Then what does cause the leaking? Disuse?

yes they swell up and leak/burst

 

[JHZR2]

I’m considering doing it on some of my older cars. They don’t have computers per se, but they have an idle control that works faster and in a wider range of scenarios than a human can.

Report here was only one cap was good:

https://www.peachparts.com/shopforum/diesel-discussion/389414-eds-elr-idle-issues-om603.html

 

[blkwtr]

When my Lexus L400 was acting up for no apparent reason, I checked the ECM and found a leaking capacitor. I replaced all six of the ones on the board and solved the problem for about $20.00.

 

[dfarr67]

Just get a tested spare ecu and fix when oe goes out- which may be never.