LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

P0135, p0420, p0430

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Old 08-07-15, 02:27 PM
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waqas300
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Default P0135, p0420, p0430

My 98 LS400 display error upon scanning the ecu.

P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1)
P0420: Catalyst System Efficiency Below Threshold (Bank 1)
P0430: Catalyst System Efficiency Below Threshold (Bank 2)

please help.
Old 08-07-15, 03:05 PM
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RA40
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Miles/km on car?

Replacing the O2 sensors along with checking the exhaust system for any breaks/leaks. Do both bank 1 sensors on each side. Your car is likely running rich initially so I would also suggest the ECT sensor. Do this soon. If your car requires the cats for annual renew in your country and an error code is read resulting in failure, replacing the cats will be expensive. The O2 sensors and ECT is under $150 stateside if you can DIY.

The cats are pretty durable but excessive unburnt fuel run through them will ruin them quickly. I would imagine that they could be hard to source if not pricey to import.
Old 08-08-15, 01:09 AM
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waqas300
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Originally Posted by RA40
Miles/km on car?

Replacing the O2 sensors along with checking the exhaust system for any breaks/leaks. Do both bank 1 sensors on each side. Your car is likely running rich initially so I would also suggest the ECT sensor. Do this soon. If your car requires the cats for annual renew in your country and an error code is read resulting in failure, replacing the cats will be expensive. The O2 sensors and ECT is under $150 stateside if you can DIY.

The cats are pretty durable but excessive unburnt fuel run through them will ruin them quickly. I would imagine that they could be hard to source if not pricey to import.
Car is running over 320K miles
Old 08-08-15, 11:23 AM
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If they haven't been changed those O2 sensors had a good long life. The PCV valve as well and this is another low cost part to replace. Just be gentle with the PCV grommet on the valve cover. They get pretty brittle with age and break apart when removed.
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