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Discussion Starter · #1 ·
When I drive in "D" my CEL "check engine light" will come on, but it will not do it if I keep the truck in "4". It is as if I am not getting a high enough RPM to run efficiently and the sensor trip the code "P0430". I can drive all week in town in 4, and the CEL never trips, but it is in town driving, so my RPM is about 1500.
I bought this from a guy who like to wheel alot in AZ; super dusty environment and the Air filter showed it. I wonder if the MAF Sensor needs replaced?
Toyota cats are built to last forever, but the sensors take a beating....
Anyone else have this issue, and how did you solve it..
 

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You didn't mention the model year or odometer reading of your FJ, this is important to understanding what might be going on. If there is more than ~ 90K miles on the vehicle, do you have maintenance records indicating that the fuel-air and oxygen sensors have ever been replaced?

There are several types of sensors that provide data to the engine ECU to control the fuel-air mixture, and one sensor that monitors the catalytic converter efficiency:

1. The Mass Airflow Sensor in the engine air intake tract. This measures the amount of air entering the engine, and eventually will get contaminated and will provide inaccurate air flowrate data to the ECU. The MAF sensor is easily cleaned, and essentially lasts forever if it is not accidentally damaged during the cleaning process.

2. The 'upstream' fuel-air sensors in the engine exhaust manifolds. These broadband sensors monitor the oxygen content of the exhaust and provide real-time feedback to the ECU for adjusting the volume of fuel injected, attempting to maintain the 'ideal' 14:1 air-fuel ratio. These sensors have a finite lifespan of ~85 - 120K miles, and MUST be replaced periodically.

3. The 'downstream' oxygen sensors in the exhaust system. These are behind the 2nd catalytic converter, and also measure the oxygen content of the exhaust gas, but are utilized to gauge the overall efficiency of the catalytic converter system. These also have a finite lifespan and MUST be replaced periodically.

After cleaning the MAF sensor, use an OBD scan tool to clear the P0430 code, and find somewhere where you can put the engine under substantial load for at least several minutes to get the catalytic converters up to peak operating temperature and burn off any deposits that have built up over time. Ideally, this would be a long, steep mountain grade that requires a relatively large throttle opening, and maintain an engine speed at least 3500 RPM for 10 minutes or longer. If the grade is short, repeat this several times in rapid succession to get the cats nice and hot.

If you have no steep grades nearby, then it will be harder to put the engine under load for a sustained period of time. A run on the highway in 4th gear at the highest 'legal' speed for 10-15 minutes may be your only alternative.

If the P0430 code returns again after cleaning the MAF sensor, the next step will be to meticulously inspect the exhaust system for any leaks, and then replace both fuel-air sensors, using ONLY original Denso "OEM identical" parts.

If the P0430 code returns again after replacing the fuel-air sensors, replace both downstream oxygen sensors.
 

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Discussion Starter · #5 ·
Deep cleaned the MAF, replaced both downstream O2 Sensors with Denso OEM sensors...
Run great. No codes. improved mileage.
Previous owner bought "autozone" parts, so he may have put a non OEM O2 sensor in...
Who knows.
 
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