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If you have any problem obtaining a film capacitor at the link, you can use any film capacitor ranging 0.047uF to 2.2uF picking up from a broken TV, VCR, PC power supply, radio or some electronics gear. The purpose of the capacitor is to eliminate the DC and only passes the AC component.
I dare used 0.47uF, but it is not very strict, 0.047uF is still mostly OK although the read-out voltage may be a bit low depending on the impedance of a multi-meter.
Regarding the withstand voltage, higher than 6V is acceptable because the line has only DC5.0V + ripples.
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.
I really appreciate this entire thread on this forum, both replacing the caps and the pretest. However, I replaced all of the capacitors (with good one) on my '93 LS 400 and still have some issues. So I thought I would now go back and do the pretest. I had an extra 47 uf cap from my order with Digikey so thought I would try that. My results show between 5.4 to 6.9 mv. I think this shows all to be well but wanted to double check since I used the 47 uf cap instead of a 0.47 uf. Am I misreading something? Everything was dead cold with the engine just started.
I really appreciate this entire thread on this forum, both replacing the caps and the pretest. However, I replaced all of the capacitors (with good one) on my '93 LS 400 and still have some issues. So I thought I would now go back and do the pretest. I had an extra 47 uf cap from my order with Digikey so thought I would try that. My results show between 5.4 to 6.9 mv. I think this shows all to be well but wanted to double check since I used the 47 uf cap instead of a 0.47 uf. Am I misreading something?
I actually may be misreading my voltage meter. That might not be 6.9 mv but 69 mv. I use this meter perhaps once a year, mainly for DC readings. Any opinions are appreciated.
I really appreciate this entire thread on this forum, both replacing the caps and the pretest. However, I replaced all of the capacitors (with good one) on my '93 LS 400 and still have some issues. So I thought I would now go back and do the pretest. I had an extra 47 uf cap from my order with Digikey so thought I would try that. My results show between 5.4 to 6.9 mv. I think this shows all to be well but wanted to double check since I used the 47 uf cap instead of a 0.47 uf. Am I misreading something? Everything was dead cold with the engine just started.
Using a 47 uf polarized capacitor.
My readings were .054 to .069
Electrolytic capacitors have some leakage current and a 47uF is too big to pick up the energy from the ignition cycle. This doesn't provide you any authentic result. Use a film capacitor 0.47uF and measure correctly. Also don't forget to twist the proving wires to avoid the interference form ignition wires.
Electrolytic capacitors have some leakage current and a 47uF is too big to pick up the energy from the ignition cycle. This doesn't provide you any authentic result. Use a film capacitor 0.47uF and measure correctly. Also don't forget to twist the proving wires to avoid the interference form ignition wires.
Thank you Yamae for replying to my post, I truly appreciate it. A couple of things I need to mention is that my car is a 93' LS 400, Calif. ECU 89661-50150. The Op1 connector is missing from the module as mentioned in another post so I use the "temp" connector. I have obtained a 0.047uf film cap as Cowboy has previously posted this as an OK cap. My readings now on a warm engine (I will test again when cool) are 058 volts or 58 mv +- 6 mv.
A couple of other items. The engine temperature needle barely gets off cold even after 20 minutes of driving. Could the coolant temp sensor be the problem? The check engine and Trak lights will come on for about 5 minutes and then turn off. I had the car in for smog inspection today and it passed all of the emissions tests until the check engine light came on and the technician had to fail the car. It does idle rough at about 600 rpm. Lastly, when I replaced all of the caps I may have disturbed the negative solder point for the 47 uf cap. Using an eye loop I cannot find it on either the top or bottom of the board. The positive connection is an obvious, wide trace. Can you point me to where to look for the - trace so that I may consider repair if necessary. Thank you very much.
Thank you Yamae for replying to my post, I truly appreciate it. A couple of things I need to mention is that my car is a 93' LS 400, Calif. ECU 89661-50150. The Op1 connector is missing from the module as mentioned in another post so I use the "temp" connector. I have obtained a 0.047uf film cap as Cowboy has previously posted this as an OK cap. My readings now on a warm engine (I will test again when cool) are 058 volts or 58 mv +- 6 mv.
A couple of other items. The engine temperature needle barely gets off cold even after 20 minutes of driving. Could the coolant temp sensor be the problem? The check engine and Trak lights will come on for about 5 minutes and then turn off. I had the car in for smog inspection today and it passed all of the emissions tests until the check engine light came on and the technician had to fail the car. It does idle rough at about 600 rpm. Lastly, when I replaced all of the caps I may have disturbed the negative solder point for the 47 uf cap. Using an eye loop I cannot find it on either the top or bottom of the board. The positive connection is an obvious, wide trace. Can you point me to where to look for the - trace so that I may consider repair if necessary. Thank you very much.
Judging from your words,"about 5 minutes", I would check the pre-cat O2 sensors. It should be sending a good 0.8Vp-p signal to the ECU after 5 minutes engine running.
Regarding the negative solder point, it is the ground line. If the line is damaged, try using a nearest ground instead of the original hole. Also put an additional wire to that trace in order to minimize the ground impedance.
Judging from your words,"about 5 minutes", I would check the pre-cat O2 sensors. It should be sending a good 0.8Vp-p signal to the ECU after 5 minutes engine running.
Regarding the negative solder point, it is the ground line. If the line is damaged, try using a nearest ground instead of the original hole. Also put an additional wire to that trace in order to minimize the ground impedance.
I will check the pre-cat sensors and do a temporary grnd connection to test the 47 uf cap to learn if that makes a difference. That should be an easy test, I hope.
I may have not completely explained the situation. While driving for a while, engine fully warm the check engine light and Trak light will come on and stay on for about 5 minutes and then turn off.
I did recheck the e1 to temp reading after the engine cooled. It now reads 42 mv which I believe may be within the acceptable window.
Thank you for the very detailed information. I think this test for the OX1 and 2 sensors is an excellent addition to this thread, I am sure others will benefit from it.
I drove the car for about 30 minutes to be sure it was welled warmed and past the on again off again check engine light. I then took my readings at 2000rpm. I had really hoped this would be the smoking gun but my readings for both bank 1 and 2 sensors was 0.4-0.6 volts. I tested several times using different voltmeters, both agreed.
I am back to ground zero. My only other thought is the slow warm up time for the engine, at least according to the displayed temperature gauge. Would a bad thermostat cause the problems I am experiencing with rough idle, low power and the engine check light and TRAC-OFF lights coming on for a short duration and then off?
I have replaced all capacitors with the recommended brands, replaced the coolant temperature sensor, plugs and ignition wires. Without any error codes I am not sure what else to look at.
11-16-14, 06:38 PM
- by measuring the ripple voltage live while the car is running! - my nomination for best time-saving post of 2013 
