e30antonio

[Edit 5/24/21... Solved: The Check engine light for p0430 is still not back on and has been off by itself for about 1500 miles now - even after clearing the code with a scanner, it hasn't lit up again. It seems that fixing a pcv valve vacuum leak at the hose and/or replacing the downstream O2 sensors solved the issue.]

I have a p0430 "Catalyst system efficiency below threshold, Bank 2" light on my 2000 LS400. Using the Torque Pro app, here is what I got for the O2 sensors on both banks with the engine at temperature and at idle. The green spikes are where I brought the revs up to about 1700 RPM.




Both pre-cat sensors look like they're doing fine. The after-cat sensors seem to be constant but very low in voltage.

At first, I had a p0171 System Too Lean, Bank 1. So I swapped sides with the pre-cat sensors. Then I got p0171 again. Then, I fixed some vacuum leaks and cleaned the MAF. Now, I'm stuck here on p0430.

Your thoughts?

relentLS

By the looks of it, either both of those post cat O2's could be tired, the cats themselves are tired, or there is something else causing the engine to not burn quite right, although the pre-cat sensors look pretty good, but possibly a little on the lazy side. Notice the bank 2 sensor 2 voltage never hits 0 while the bank 1 sensor does. It technically should be hitting 0 volts when the engine goes into fuel cut off mode. To test it, try getting up to cruising speed on the highway and coasting in gear. If it's functioning properly it should hit 0 volts. To verify the engine is in fuel cut off mode, load the setting on your scan tool that tells you whether it's in open loop or closed loop operation. You should observe the engine go from closed loop to open loop mode and the O2 sensor voltage hit 0.

Yamae

Those O2 sensors are all working OK since the voltages are swinging lower than 0.1V to higher than 0.8V. The waveform of post O2 sensors are very strange. Those should not swing that fast and should not show the similar waveform like the pre O2 sensor. The fast swinging means that the catalytic converter is not working well. There are several reasons why so. It needs some skills and equipments to find out the root case of it. I'd check the air leak first.

e30antonio

Thanks. I did that today. At operating temp, I got up to 60 mph. Then I let off the gas and let it decelerate by itself. Once the status went to "Open Loop", Bank 2 Sensor 2 flat lined and sat at 0 V So, evidently it is functioning fine? I did not check the Bank 1 Sensor 2 however.

Also, my Evap system and catalyst system is taking a while to complete (it has been on "Incomplete" for about 250 miles now). Not sure if this is related.

e30antonio

Are you referring to the spikes when I rev the engine, and how Sensor 2 mimics Sensor 1? Or the lower parts when it's at idle?

Superfast1

I had the exact problem on my 97 LS & it took me a very, very long time to troubleshoot & pinpoint the issue. It turned out to be a bad MAF Sensor connector (electrical intermittent at 1 or more of the 5 pins) so here's what you should try: Hookup the OBDII scanner, let the car warmed up for like 10 mins for it to go into the close-loop mode. Once it's warmed up, instead of monitoring the O2 sensor voltage waveforms, I would look at the LTFT (Long Term Fuel Trim) of both banks. If 1 or both banks are running lean (P0171), the reading should be in the +18% to +25% or higher. If they're running rich then the reading will be -18% to -25% or lower but that's fine as this is your staring point. Now wiggle the MAF Sensor connector or the 5 wires & observe the LTFT's. When the car is running, the ECU will keep on adjusting the fuel trims between rich to lean condition so in a normal operating condition, both fuel trims should be close to +/- 0%. The waveforms that you see at the upstream O2 sensors (pre-cat sensors) are the representation of the lean to rich conditions when it's switching from rail to rail (0 to 1V). It may take a minute or so for the LTFTs to change & if they do change & go back to normal (close to +/- 0%) then you've found the problem. Good luck.

YODAONE

Inspect negative battery cable ground points, engine to chassis ground cables and wiring harness ground points.

Negative and Postive battery terminals.

Is your alternator and battery in good condition?

Any voltage drop?

Replaced MAF on 1999 after 170,000 miles. Despite cleaning with MAF cleaner, the sensor was tired.. Part throttle acceleration improved with new Dealer purchased unit. Aftermarket parts are dicey.
Be sure MAF includes the special MAF gasket. It is not sold separately. Mine did not and Toyota has still not addressed this 7 months later...

one thing to check on MAF mounting:

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/943854-mass-airflow-sensor-leaks.html

Numerous forum posts on real benefits of changing the ECT sensor...if original, yours is probably expired. Use dealer part.

e30antonio

I'll try that out and report back.

e30antonio

I'll recheck the engine grounds. The battery (650cca / 24F) is new and the alternator is new as well - less than 500 miles or so are on those components.

Do you happen to have the genuine MAF part number?

Any way to test the engine coolant temp sensor? That's the one on the driver side bottom corner of the radiator, correct? I'm sure it's original.

YODAONE

If original coolant sensor, then replace...located on right front of engine. (Not on radiator)

Coolant temperature sensor # 89422 in parts diagram.

e30antonio

I haven’t done much further fixing or troubleshooting yet. However, I swapped in some known-to-be working O2 sensors for the pre-cat spots, just for the heck of it. They seem to be no different though.

These are my readings after a 20 minute drive. This is me sitting at idle. The only thing I see is the B1S2 is always sitting at 0v. Is that fine?

Yamae

Staying nearly 0V simply means that there is enough oxygen and the O2 sensor can not generate at all as long as the sensor is not dead. Your first post shows that all sensors are fine swinging enough like less than 0.1V to higher than 0.8V. This simply means that your sensors are not dead. A good O2 sensor generates more than 0.8V when heated under the condition of no oxygen. When there exists enough oxygen, voltage drops and it goes down to nearly 0V. The fact simply means that your car's B1S2 sensor is detecting too much oxygen. There must be a reason why so. One of the reasons is the air leak coming in from somewhere.

Your first post shows that both red lines indicate good combustion situations. This simply means that the fuel to air ratio is good. But green lines show strange activities although the amplitude is enough. I suspect that there is an air leak. You'd better to check the crack of pipes and flanges very carefully all the way after the pre cat O2 sensors.

relentLS

Yamae is correct. Those fuel trims are too high, meaning there is a vacuum leak somewhere in the intake system, or an exhaust leak letting air in tricking the O2 sensors into adding fuel. Those are the most likely causes.

e30antonio

Thanks all for the replies. I will continue to look for air/vacuum leaks. I haven't checked for exhaust leaks yet.

Here's what's going on now: the check engine light went off by itself about 300 miles ago. As of today it still hasn't came back on (I've been using the LS as my daily, so lots of back and forth driving). The main problem now seems to be that my catalyst system is still "incomplete." I put in a new battery about 500 miles ago. Surely that's enough time to reset after unhooking the battery?
My evap system was taking a while as well but it's now complete.

The engine seems to take a long time to get to operating temperature (that is, the needle holding in the center of the gauge). I timed it and it's just over 7 minutes of normal driving for it to hit operating temp. My guess is the thermostat is stuck open.

I have a parts engine so I'll swap thermostats and see what happens.

YODAONE

Anyone with an original thermostat should replace it. Time-degradation or high mileage rubber seals tend to improperly seal and, or, hang open the thermostat - which happened to me. Replace with OEM thermostat
Avoid aftermarket junk.

See:

https://www.clublexus.com/forums/ls-...hermostat.html