LScowboyLS

Note: the following post by Yamae details how you can check for bad ECU capacitors without even removing the ECU from the car - by measuring the ripple voltage live while the car is running! - my nomination for best time-saving post of 2013





The photo shown above is a method of how to check ripples by simply using the diagnostic connector located on your Celsior/LS400. All you need are just a good multimeter and a specific inexpensive capacitor. What I mean by "a good multimeter" is that the meter can measure up to 300KHz or higher.

Measure the AC voltage (~) between "OP1" and "E1" in series with a film capacitor 0.47uF or so to eliminate the DC. (blocking capacitor is the orange colored component in the photo) - good choice for this cap here for 41 cents

Celsior's "OP1" is internally connected to the engine temp sensor and "E1" to the signal ground of the ECU. I think LS400s 94-00 are the same. The desired read out voltage is roughly speaking 40mV RMS or less.
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Below is a technical explanation for those who are interested in the detail:

The engine temp sensor is supplied the 5V regulated DC from the ECU via a resistor and you can measure the ripple voltage "Er" at this point some. In other words, the engine temp sensor is pulled up by a resistor to the DC 5V in the ECU. So you can check the ripple without opening the ECU box.

The relationship between "Er" and "real ripple voltage" are calculated as follows.

"Er"="real ripple voltage" X "temp sensor's resistance" / "(internal resistance in the ECU + temp sensor's resistance)"

The "real ripple voltage" is calculated as follow.
"real ripple voltage"= "Er" / "temp sensor's resistance" / "(internal resistance in the ECU + temp sensor's resistance)"

Roughly speaking, the "real ripple voltage" is about 25% bigger than "Er" when engine is cold. It is several times bigger than "Er" when engine is fully warmed up because the "temp sensor's resistance" varies depending on the engine temperature.

My 98 Celsior's capacitors were all replaced already as a preventive measure and the resulting reading was only 5.4mV when engine was cold.

Regarding the limit voltage, see the post # 218. Those values are when measured by an oscilloscope and are the peak to peak voltage at the removed connector terminal of the coolant temp sensor. Most of good multimeters show the RMS value. Also the "Er" is smaller than the "real ripple voltage". With these factors, I'd say the read out voltage by a good multimeter when engine is cold is preferably less than 40mV RMS (Root Mean Square)

Higher than 40mV RMS may cause intermittent problems.

python

iTrader: (4)

This should probably be stickied in my opinion to prevent every single thread being littered with incessant reminders to the ecu caps fix

LScowboyLS

every single thread is not littered with reminders to fix the ECU caps, just the huge portion where it is likely to be the problem (i.e. any drivability, transmission, or A/C problem, ECU caps should be one of the very first suspects), as this is a known defect of epidemic proportions!

This is because, outside of ECU cap failures, Lexus's are extremely reliable as far as engine, transmission and A/C, so it's only logical that you want to check the most likely culprit on systems that don't usually fail!

Especially to a new person on here, they may have no idea how common the ECU capacitor issue has become in the last year or so!

python

iTrader: (4)

then the over abundance of ecu caps fix needs to be pointed in the direction of a fail safe test procedure..such as this,if in fact that's what it is..so giving direction how to test is a much better way

ScotLex93

I recently bought a low mileage mint example 1993 LS400. However, while inspecting the engine bay of the car today I noticed that a bridge consisting of a wire and 2 connectors had been made in the diagnostic fuse box connecting WA (ABS ESU) & WB (ABS relay). Can anyone tell me what this means? Is there a problem with my ABS ECU which the seller hid from me? I took it off to see what would happen, but it didn't appear to make any difference, no warning lights, etc came on. I put it back just in case it's removal would cause any harm to the car.

LScowboyLS

It means someone jury rigged it, I would remove it


likely (at least in his mind, there was)


wait for rainy weather, clear the codes in the car completely by disconnecting the negative battery cable for a few hours after you have completed the removal of wire bridge crap

then drive the car (and avoid real emergency braking situations, just in case the ABS has an issue) and then find a wet, slick, but safe area, such as a large empty parking lot and slam the brakes on in the car in such a way that would normally force a skid in the rain, this will force the ABS to engage, and then note the following:

● did the ABS kick in and work as it should (you should be able to feel the ABS take over and the stopping distance will make it obvious whether it worked or whether you just skidded because it did not work)

● especially if it did not work, an ABS diagnostic code should now be generated that can be downloaded using the instructions here - then you can properly address the problem if there is one!


In any event, little jumpers that modify the factory wiring are never a good thing, except in the case of a test!

MattLS400

Great Thread ! This would be helpful to alot of us in this forum !

LScowboyLS

For anyone planning to do Yamae's ripple test, if you need this special capacitor in order to conduct the test, PM me and I will mail you one out for free!

Pfucterpus

I tried to PM you but it said i was not chosen.

BCinDC

I was excited to try this tip, but after receiving my capacitor, I discovered that the "OP1" slot on my 96 is empty . There is no OP1 slot on the DLC2 under the dash either.

Any other connection location that will work?

Yamae

This post will be helping you.

BCinDC

Thanks, I'll give that a try. I had thought about using one wires on the the Coolant Temp Sensor (which I'm pretty sure is bad, and needs to be replaced anyways), but was hoping for a super simple alternative

Screwhead

I need help donducting this can u help ??

sha4000

iTrader: (1)

He has not been active in this forum for some months.

AHJ

Hi

It looks like you are looking for the capacitor. Unless, someone more helpful comes along, here's my take on what you could do.

1. Print out the data sheet supplied by Yamae: http://www.digikey.com/product-detai...4544-ND/111793

2. Take the printout to a local electronics components shop. The sheet says its at end of life - any value close to it is ok as its just there to block off the dc component.

3. This capacitor does not have a positive/negative terminal so it does not matter which end you have at the meter and which end at the test point.

4. Almost any junk electronics box should have some of these. If you like to take things apart then here's another reason. Make sure its unplugged and actually if you know as little as I do then best to stay away.The old crt tvs can be lethal.

For the store, google Electronics components and the name of the city you live in. Houston or Aspen or wherever. for example: Electronics components Houston.

Aspen's a University town with a music scene so you might have better luck there.