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98 Chevy Tahoe. OBD codes P0420 and 0430. What should be the first thing to check? Gotta get this fixed to pass emission for registration. Thanks!


those codes are for cat.

those codes are for cat. converter in exhaust.
most of the time it means a new cat.
some times the sensors read wrong, just right to give a false cat code.
with that, i mean the sensors are used to monitor cat performance, so if the sensors are off, the cat might get blamed for a emission false reading.
what needs to be done is a o2 sensor test, and if it passes, then a cat. monitor.
real easy with a scan tool or a shop with a half a clue.
you just have to watch the up and down o2 sensors readings on scan tool to see if they match, if so new cat, if not, recheck sensors or wiring for intermitten problems.
just a little info in case you are going to a shop for repairs, you'll have a bit more understanding and see thru any bs

Catalyst System Efficiency

Catalyst System Efficiency Below Threshold (Bank 2)
What does that mean?
Basically this means that the oxygen sensor downstream of the catalytic converter on bank 2 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms
You will likely not notice any drivability problems, although there may be symptoms such as a rough/hard idle when cold.

Causes
A code P0430 may mean that one or more of the following has happened:

1. The catalytic converter is no longer functioning properly
2. An oxygen sensor is not reading (functioning) properly
3. There is an exhaust leak

Technical DescriptionCatalyst System Efficiency Below Threshold (Bank 1)

What does that mean?The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms
You will likely not notice any drivability problems, although there may be symptoms.

Causes
A code P0420 may mean that one or more of the following has happened:

•Leaded fuel was used where unleaded was called for
•An oxygen sensor is not reading (functioning) properly
•The engine coolant temperature sensor is not working properly
•Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
•Retarded spark timing
•The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible SolutionsSome suggested steps for troubleshooting a P0420 error code include:

•Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
•Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
•Inspect the downstream heated oxygen sensor (HO2), replace if necessary
•Replace the catalytic converter
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

www.obd-codes.com

get it fixed yet? let us know

get it fixed yet? let us know

check for O2 sensor voltage

check for O2 sensor voltage switching at least once per second whil the engine is running while in closed loop. (you'll need a scanner which can monitor these sensors)

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