LScowboyLS

looking good

LScowboyLS

One hint for others doing this DIY, when there is bad leakage, you may be better off starting with another used ECU of the same part number that is currently working correctly and does not have visible leakage yet, as the electrolyte damage will make the process of removing and installing the capacitors much more challenging.

If your ECU is badly damaged like in some of the photos, consider finding a "virgin" ECU that has not been repaired and has not yet leaked, the ECU cap replacement will go much smoother!

Sedgwick

LScowboy,
I have a 1994 GS300 that consistently displays a 41 & 71 fault codes along with “check engine” & “TRAC OFF” and the “TRAC” light comes on intermittently, I haven’t been able to interrogate the codes when the “TRAC” light is on. I have found some old posts that talk about this but haven’t found any resolution. Below is what I have done so far.

For code 41 I replaced the Throttle Position Sensor, for code 71 the EGR valve has been cleaned and the EGR gas temp. Sensor replaced. After replacing these parts and clearing the codes they come back within 20miles of driving. Your post regarding leaking ECU capacitors is very interesting and informative; my GS has the following issues that you listed in your first post.

● random dropping into "limp home" mode
● weird shifting problems
● engine runs like crap, then suddenly runs fine again
● transmission jerks from 1st to 2nd gear, and kinda slips from 2nd to 3rd

My next step is looking at the ECU. In your post you list capacitors for the LS400 do you have a suggestion for a 1994 GS300?

LScowboyLS

the GS300 ECU is very easy to remove, I would pull the ECU, and make sure you are wearing all cotton clothes and bare feet (for static protection), carefully open the ECU and photograph the circuit board(s) inside and post them here and also post a list of the capacitors and the writing on each one here, and I will respond with links on which exact capacitors you need to order.

Sedgwick

Will do.

Thank you.

LScowboyLS

All LS400 owners should seriously consider doing the ECU capacitors, or having someone recommended to do them with the correct caps specified in post #1 of this thread.

The reason is, it is a known defect area, and if you wait too long, then the leakage will end up ruining your ECU, and then you have to buy another ECU on ebay, and then have that ECU retrofitted with new caps!

So it is kind of a proactive repair, but the cool part is, it often solves many weird issues as a bonus, and it also tends to result in more low end power and better gas mileage!

Unfortunately, I have never seen anyone who sells these "rebuilt" who is using the correct capacitors, so do it yourself, or else find a great solderer and have him do it with YOUR parts only!

roydarc

Thanks LScowbowLS and Yamae for the information on the problems with the ECU and repair. I have a 1995 Lexus LS400 and have been getting error codes P0300, P0302 and P0308. Changed spark plugs and wires along with Oxygen Sensors but to no avail. After seeing your article on the ECU I pulled mine and found one capacitor leaking with the positive leg corroded away. I also found two other capacitors beginning to leak. Followed your instructions to the "T" replacing all six capacitors and now not only are the error codes gone but the vehicle is running a lot smoother and has more pep.
Again, THANKS!

Yamae

Thanks for the report, roydarc. It is our pleasure that you succeeded to fix your LS400. Your report will encourage people who are about to do the job.

sh99ters

Where can i go to get this work done?

silos5

iTrader: (3)

get capacitors from the links in the 1st post and find a good solderer. Mine was done by the guy who sells and repairs PCs.

LSjuan

Hey LScowboy I wanted to know if I can use a 93-94 ECU from a SC400 so I can use on my 93 LS400

LScowboyLS

No

It might work in an emergency to get you home, but several subsystems would have problems.

L8274Jones

Hi LS CowboyLS,
Something I forgot after tuning up this 95 LS 400 I have it kept throwing a PO 300 Misfire random code for a period of time and then stopped ..... I do not know why but it stopped that on it's own .... that was the real start of my mystery..... those misfires may have been false ???

Sedgwick

LSCowboy, Below are some pictures of my 1994 GS 300's ECU. None of the capacitors show any signs of leakage so I'm not sure capacitor replacement is needed. Both PC boards looked brand new.

List of capacitors:
H9337 105 C
H9335 105 C
H9341 105 C
H9340 105 C
47uf60V

Thank you for your help.

LScowboyLS

that's how mine looked the first time I checked them, then a few months later I checked them again, out of desperation, and the leakage was so bad that the ECU was very close to being ruined permanently.

Just because a capacitor looks fine, doesn't mean it is. The original Nichicon PF (M) caps were not only a defective series, even if they hadn't been, they were never meant to go beyond about 12 years, and yours are 20 years old

have you tried Yamae's ripple test? - It should be quite similar on a GS300. - I have the test capacitor if you need one.