LS400_96

I am getting a CEL for codes 420 and 430 on different occasions (Catalyst System Effieciency Below Threshold -- Bank 1 and Bank 2 respestively). In the service manual it says problem is either 3-way cat or O2 sensor. I have about 125,000 miles on my car and I dont think the previous owner ever changed any of these (checked and looks original).

I think the problem is the O2 sensors but am hearing LS400's 95 and up are having problems with catalytic converter. I have been getting this CEL for quite awhile and even passed a smog check a couple of months ago after clearing the CEL by taking the fuse out for EFI 1.

I have two questions to ask.

1) Have any of you guys changed your catalytic converters cuz they were not working for these years?
2) Do you guys think the catalytic converters need to be replaced or just the O2 sensors?

Nick T

LS400_96,

The O2 sensors are technically a wear item, therefore they should be replaced anyways. Use a infared thermometer ot check the inlet and outlet temperatures of the cat. Cats don't usually fail, a bad cat is more likely because a rich mixture has passed through it melted/blocked the passages. A large difference in temperatures between the inlet and outlets of the cat will mean it's blocked.

In any case, a blocked cat doesn't usually cause a CEL, I would lean towards a bad O2 sensor in your case.

Regards

LS400_96

Where could I get a infrared temp sensor. How much do these go for? Would a blocked cat cause a smog check to fail. Cuz I did a smog check awhile back and passed. I just turned the check engine light off by pulling the EFI 1 fuse.

Nick T

LS400_96,
Have a mechanic with the proper tools check for you. A good 1,000 degree infared thermometer can be bought from various tool trucks but cost $200-500. A blocked cat usually won't cause emissions failure, just lost of power.

regards

VVT-i

My respone on your another thread
https://www.clublexus.com/forums/sho...threadid=92334
Or get a tech to hook up the scan tool and go to O2 rpm check(with Lexus scan tool). The bank 1&2 sensor 1 should respone rapidly and the wave form is moving up and down between 0.1-0.9 volt. The bank 1&2, sensor 2( after the cat) will stay at 0.15 volt for about 3-7 seconds and then it will jump to around 0.7-0.8 volt. This is normal for the sensor 2 (post cat), it not suppose to move up and down just like the sensor one(before cat).

LS400_96

Okay this is what I did today...

I warmed up the engine for about 2 min. and raced it bet. 2500 to 3000 rpm for about 3 min.

Then, I directly probed into my ECM to ports OXL1, OXR1, OXL2, and OXR2 to E1 with my multimeter. Since I don't have a scan tool.

Basically, this is the voltage readings I get when in idle after above.
Bank1 Sensor1 (OXL1)
-- .06V to .85V. Voltage change very fast. Could only see lower voltage and upper in bet. get overload reading.

Bank2 Sensor1(OXR1)
-- same as OXL1, identical readings

Bank2 Sensor1 (OXL2)
-- .7V to .85V. Pretty steady. Stay within this range.

Bank2 Sensor2 (OXR2)
-- same as OXL2, identical readings

When rev to about 2500rpm, the voltages of all sensors are low, below 1V around .035V.
What do you guys think?

ndauderman

California '95 LS400 owner. 129,989 miles. I received the CEL for the 420 & 430 code. Had the CEL reset several times by the Lexus dealer (nudge, nudge, push). Each time, I was told I needed to replace my cats. At the same time, I was considering a new exhaust system to give the car a modest testasterone boost. So, I went ahead and replaced the two cats off the manifold with aftermarket cats, kept the third OEM cat, and had a new aftermarket exhaust system designed and installed with 2.25 piping. Needless to say the car sounds very healthy with a moderate increase in performance. However, I did not, and have not yet replace the O2 sensors. I have twice received the CEL light (420 & 430 codes) since the new system... very frustrating.

Before I replace the O2 sensors, has anyone had success in avoiding the 420 & 430 codes by replacing the O2 sensors?

Also, I was told that in some of the LS400 models, there may be an exhaust leak off the manifold - can anyone verify this?

Thanks,

Nick