I have a 2003 RX300 with a bad ECM.
I am looking for information on replacing one of the capacitors on the ECM that looks to be burnt out.
I have been unable to find any information or diagram on the actual ECM motherboard, so I can troubleshoot the issue. Also, I have been unable to figure out a part number as I am not familiar with capacitors, and I do not know the meaning listed on the part.

Any help or guidance would be greatly appreciated!

I do have photos of the board, front and back.

The capacitor has this printed on the top:

100
10G
2P7

 

Quick reply ... check with distributor like Mouser
Looks like 100uFd

Part will not be sold by Lexus ..

I would desolder it (can be difficult) and check it with a new VOM which can read/check caps.

Will try to find more details for you.

Salim

 

Thank you... I will look into that!

 

Also check with DigiKey

SMT electrolytic is the type.

Also check in SC300/400 Forum 'ecu' 'electrolytic capacitor'. Pre 1995 models had a bit of problems.

Do not buy off the shelf capacitors for repair.

You need to worry about Temp and low ripple impact. I dont want to hash it out there as all have been discussed in Sc forum thread.

There is a Engineer from Japan who has put in lot of effort in explaining this .. sorry the name escapes me.

Salim

 

100 --- 100uF
10G --- 10V
2P7 --- ID code

If you find that capacitor is not good, replace it selecting one from the series UCX or UCZ in the chart. If not available, UCI or UUB may be OK to use.
The detail can be found at below.
http://www.mouser.com/pdfDocs/Nichicon_Automotive.pdf
http://www.nichicon.co.jp/english/pr...hip/index.html

 

Thank you Yamae. I had forgotten your user name.

Things can fail, but have you come across this type of caps to fail ... we are talking '98 or later year of production. Although the vehicle is 2003

PrisyChrisy, be mindful of the dark painted edge. Please match that side as you install the replacement [electrolytic have a + and - .... you may be aware of this already]


Salim

 

Yamae....
Thank you so much for the info!
I still have much to learn before I try this by myself... I've read your other posts and cautions, so I am
Carefully weighing my choices and options before diving in!
You have provided more information than any technician has been able to offer... So thank you!!

 

Thank you for all your help! This info has been so great!

 

I believe the failure came from a leak in the vehicle. We got a lot of snow and the car was not working and I was unable to fix the leak at that time. I have since fixed the leak, removed the mold and found that the condensation was running down the inside of the windshield behind the dash... There was moisture in the glove box and surrounding area, so I had taken most of that apart hoping to dry it out and not damage the ECM. Unfortunately, when I fixed a few other problems and then replaced the battery and tried starting her up, she was cranking, but not starting. I also noticed that the check engine light did not come on at all, the vehicle security system was not on at all, checked all fuses, spark... And was convinced it was a bad ECM. A neighbor is a mechanic with lots of expensive tools, and came with his top end code reader only to confirm my guess of a bad ECM. No communication message received... Equals, bad computer. So I pulled it out of the car to inspect.
There was minimal rust on the metal enclosure, and the board looks great except for the one capacitor that has a burnt look on the side of it. I need to do some closer inspection on more of it, but the rest seems to look fine.
I know replacement of the ECM is costly and a new one needs to be programmed by Lexus which is very costly, so I am trying to see what I can possibly do on my own first.
That's the story!! Fun times huh! Lol

 

Toyota/Lexus/Denso have not been using QAS capacitors any more since the end of the last Century and there should not be the severe leaking problem on newer cars.

Usually when a capacitor is burnt out, there must be some reasons to be so.

PrisyCrisy wrote," looks to be burnt out" and I assume that it's not the leaking problem but there must some problem. Without analysing the ECU myself, I have no idea what is causing the problem.

Anyway it is one of the ideas to replace the burnt capacitor. The real troubleshooting may be starting after that, I think.

One thing I must add is that the upper side capacitor C115 = 200uF/10V seems to be mounted in parallel with the lower side 100uF/10V. It is strange to me that C115 looks quite OK and the lower side capacitor is not.

I don't have any experience on any RX models and this is just my assumption but those capacitors are for low voltage regulator circuits. What I mean by this is that you probably need to check the voltages of + side of capacitors. Are those precisely 3.3V or 5.0V?

 

The leaking in the car was water, the capacitors have not leaked. I have pictures of the front and back of the board in my profile under pictures, if you want to look at the back side.
I am NOT a mechanic, everything I have done and learned so far, I've learned from asking questions, doing research and also reading the Haynes Manual. Professionally, I am familiar with electronics, but not circuit boards or what makes them work... The in's and out's of the board... This is completely new and unfamiliar territory for me. I have no idea what the capacitor (that looks burnt) goes to. I would love it if I had a diagram telling me what circuit on the board is for what... But I have been unable to find that information. All I know is... Bad ECM with no power no ground going to the car.
Money is an issue for my husband and our two little girls, so my DIY efforts are because we can't afford 2 thousand dollars to buy a new one. This car is 13 years old, paid for, and I believe has some life left in it, so I don't want to give up yet. My husband drives our leased 2015 Honda, so I am without a working vehicle until I get this thing working... And we live in the country, so I'm trapped at home. This is my predicament.

 

We can talk little more technical.
Your intuition about the ecu not getting power seems good. I would start by checking +12v to the ecu. You will most likely not find the schematic for the ecu board, but the wiring to the ecu [with color coded wires is floating around on the net]. For copyright reasons CL can not attach them here. Search may lead you to some contacts who have access to them.

The +12v then goes through voltage regulators to what Yamae mentions and these electrolytic caps then hold the regulated voltage.

Check for +12v (battery voltage coming to ECU) ... there may be various pins switched +12v, constant +12. Armed with wiring diagram you can see voltage from various sensors ... but they can be ignored to begin with.

Then check voltage on each of these electrolytic caps. Per Yamae 3.5 -5 v

Let me suggest some other options:
1. Talk to Lexus dealership. Some times they may surprise you.
2. Let dealership do the diagnosis ... they charge around $100 which may be applied towards the repair. Check with them.
3. Look for an ecu from junk yard and get at least a master key. You can swap the ecu and use your wallet ket (without the electronics next to it .. not the valet key) to start but bring the new master key next to the ignition key.

Lastly ... the probability of the ecu not getting 12v is higher than the cap going bad. You can clean the board with H20 and electronic component cleaner, but make sure it dries out before connecting it back. I would check all fuses again .. both in the engine and in the cab

Salim
Lexus service manuals can be a life saver too. See if you can locate one.

 

http://www.car-part.com/ a quick search for your 2003 ecu showed results between $50-300 . There are few companies out there that reprogram the transponders.

 

Thank you for helping me!

 

My experience with electrolytic caps is that they swell when they go bad. Looking at the photo, I see some slight discoloration on the body of one of the caps in question, but it doesn't look like any of the three are swollen.

If there was water on the board when it was powered, you probably should see some evidence of corrosion at the leads of the parts wherever the water collected. And if the corrosion actually occurred, there should be corrosion products on the board which are deposited on the board during the corrosion process and as the water dries. I also do not see any evidence of water having been on the board near the caps based on the photos. But there is discoloration (rust colored) on the upper right corner of the board on the ground plane near the heat sink.

Can you take photos of the reverse side of the PCB? both a low magnification of the entire board and zoomed into that corner as well as the at the caps in question, and anywhere else you might see possible corrosion.