Intermittent CEL *FIXED, ECU Leaky Capacitor Repair

FC Zach

FC Zach

Active member
Specs on my car:
-1992 with stock ECU
-Cruise control works
-Speedometer/Tach works
-ABS works (last I checked a few weeks ago)

Recently, my CEL has started to illuminate briefly and randomly upon start-ups and while driving (code 42, vehicle speed sensor). . not sure if it has anything to do with it but while driving it seems to happen after being on and then followed by a sudden off throttle (enough that the blow-off sings), a second or more after that the CEL illuminates and goes away.

I replaced the sensor for the cruise control years ago and it works fine (not entirely sure if this is even tied to the ECU anyways, if it was why didn't it do this before replacing it?), speedometer works fine too. Would the hub sensors for the ABS cause this? While searching for a possible cause, I recall seeing a mention of these somewhere and to check them with an ohm meter.

I haven't tried disconnecting the battery yet as I was hoping it would just stop (and mostly because I don't want to reset my radio) but it has been a few days now. If any of you have experienced this, what do you suggest?

Thanks in advance

EDIT: Edited subject for easier search
 
underscore

underscore

Well-known member
You should be able to reset the ECU without disconnecting the battery, just pull the EFI fuse.

I had this code popping up randomly on my car as well, I don't think it looks at the ABS sensors at all as mine are all removed and the code was still intermittent. I did end up replacing the speed sensor which seems to have cleared it up, though it could just be a dirty connection or loose wire. Since yours seems to happen at a time when the engine is getting a big jolt (on start amd dropping off throttle) I'd suspect either the impact is jarring the sensor enough to mess it up or the movement is flexing a wire with a break in it that's causing a momentary loss of connectivity.
 
FC Zach

FC Zach

Active member
Thank you! I forgot about isolating just the ECU via the fuse. . I'm gonna try that as well as check for a bad connection.

I thought the speed sensor was for cruise only. . So the ECU feeds off this sensor too?
 
underscore

underscore

Well-known member
My car doesn't have cruise but since it's from Japan the ECU has a speed cut at 180km/h which would need it. I think they all have the speed tied into the ECU for part of the TVSV control (using the speed + RPM to determine which gear you're in) but I may be wrong.
 
FC Zach

FC Zach

Active member
This issue has continued for about two weeks now but a day or two ago the CEL started to brighten and dim like the low fuel light so with that new evidence, I suspected the ECU. . This morning I pulled the ECU connections to temporarily connect my spare (with a ground wire between the chassis and ECU) and went for a test drive. All went well, drove about ten miles.

Once I got home I removed the ECU and permanently installed the "spare". . it was actually the original but failed due to capacitors leaking 5 years ago and has since been repaired. After that, I opened up the one I pulled and sure enough the culprit was leaky caps. . now to find the extra caps I ordered years ago to repair the original.

44449662965_293ce346b9_z.jpg


30424158227_90ed040928_z.jpg
 
underscore

underscore

Well-known member
Did you replace all the caps? I've been meaning to swap them out in my spare ECU but I haven't had the time to open it up and look up all the specs to order them.
 
FC Zach

FC Zach

Active member
No, just the two 10uf50v caps. I haven't replaced any others, just the failed ones. If it helps any, I got a really good deal for caps on eBay. . More than I'll ever need (hopefully) for a few bucks. Luckily it was a bulk pack because I would have never guessed two ECUs would have had the exact same caps leak.
 
FC Zach

FC Zach

Active member
I should also add that in the last few days, the CEL started to illuminate for longer periods than before (as well as brighten and dim). I decided to check to see if more codes were present but all I got was an erratic flashing. . that's what gave me the idea that the diagnostics portion of the ECU was bad (same as my last ECU).
 
9

93celicaconv

Member
I think this should be a sticky, given capacitors in early 1990's Toyotas were problematic (how many radios failed just due to this?).

But I'm confused about the pictures, which I think indicates two different capacitors in the ECU failed, and they look physically different. But the repair process consisted of using a single capacitor type for each of the two unique failed capacitors?

Lastly, in the pics, I can see the leak from the capacity shown on the horizontal circuit board, but I can't see a leak on the capacity pointed to on the vertical circuit board (which I'm interpreting to be the capacitor just below the screwdriver tip). How did you know that particular capacitor had failed? Or was there a capacitor above the screwdriver tip that pretty much disintegrated?
 
FC Zach

FC Zach

Active member
Yes, it is two capacitors. . . One is on the top board one is on the bottom board. They are both the same size (10uf 50v) caps.

I replaced both since they are a common problem regardless of whether there's any visible sign of leaking or not. . But these were leaking, you could see the board coating bubbling. I know it failed from visual inspection but on top of that, a previous experience https://www.alltrac.net/phpBB2/viewtopic.php?f=9&t=52355.
 
FC Zach

FC Zach

Active member
Seeing this is a common issue as of late, I have edited the subject of this thread since finding the cause to the issue in the original post to make searching easier for others.
 
R

Roreri

Active member
FC Zach, thanks for editing your thread title, it popped right up in the search, which was great.

I am beginning to observe this same sort of issue. This morning I glanced down and saw a CEL. I pulled over, checked my temps and listened. Nothing out of the ordinary. I cut the motor, started it back up, and no CEL.

I was only a mile from home, so I pressed on. I recorded the gauge cluster, and observed the CEL fading in and out:

https://youtu.be/9Rt9g-72bzo?t=93

Upon return home, I checked for codes jumping TE1 and E1 and TE2 and E, but got nothing.

On further review of the recording, I noticed that the rear light warning flashed on for a fraction of a second. The left side warning lights were not in the camera's field of view, but it's possible that the leads on my new battery were not 110% tightened down. I checked them and they were tight, but I gave them another nudge to be certain sure they were locked down.

It's possible that I am suffering from capacitor failure. I will continue to observe.
 
G

Gert

Active member
Roreri":q1b7h3o0 said:
I was only a mile from home, so I pressed on. I recorded the gauge cluster, and observed the CEL fading in and out:

https://youtu.be/9Rt9g-72bzo?t=93
Click to expand...
The CEL light is nothing more than a bulb what is getting constant power and the ECU is making ground to illuminate the bulb.
I used this CEL light for my Autronic fault codes.

Since your CEL is fading, the ECU is 'making' ground somewhere what probably is due to this capacitor thing. So your diagnose is probably correct.
 
R

Roreri

Active member
I appreciate that observation Gert, thanks much. Took it on a short drive this morning--I usually drop my daughter off at school to the sound of 80s music. Went to go grab some coffee. The CEL was on, but then wasn't active when I started it up after grabbing a coffee. Then it faded in then out by the time I got home (7km loop). So, I'll get down in the rat's nest of wires and pull the ECU and see what needs doing.

Underscore, I'm poking around in your thread and I see that you had the same sort of problem, and you replaced the caps.

FC Zach, I have your thread here to guide me: viewtopic.php?t=52355

10/10 community.
 
underscore

underscore

Well-known member
Yeah I replaced them in both of my ECUs, I can't remember if I posted pictures but they were just starting to leak (no damage to the board yet) so I got lucky. The ECU is pretty easy to pull and the soldering is a pretty straightforward job too, just make sure to ground yourself before handling the boards.
 
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