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catalytic converter .
In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.
The powertrain control module (PCM) has the capability to monitor this process by using a rear-heated oxygen sensor (HO2S 2). The HO2S 2 , located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).
bank 1 exhaust is the rear manifold towards the windshield side. Follow the exhaust down. There should be one oxygen sensor before the catalytic converter and a monitor after the catalytic converter. Be Careful.. they look the same.
Hi, P0420 code means a catalytic converter fault.
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.
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
Find the exhaust pipe under the rear bumper. Follow its progress towards the front of the car. The first big bulbous thing you will find is the muffler, keep going. The next bulbous thing you may find is a resonator, keep going. Eventually you will come to a little thingy screwed into the side of the exhaust pipe which has some wires coming from it. That is your downstream O2 sensor. Next will be the catalytic converter, next thing will be the upstream O2 sensor, then the exhaust manifold, the the head of the engine.
PO420 code is for catalyst system efficiency below threshold (bank 1) Usually it means that it is time for a new catalytic converter on bank number 1. Cylinder bank number 1 is always the bank with the number 1 spark plug in it.
On the SOHC engine the front (A/F) oxygen sensor is located in the
front section of the front catalytic converter. The rear oxygen sensor
is located in the rear section of the front catalytic converter. On the
DOHC engine the front oxygen sensor is located in the front section of
the exhaust system, just past the crossover pipe. The rear oxygen
sensor is located in the front section of the catalytic converter.
Oxygen sensor location-Baja 2.5L SOHC engine
Oxygen sensor location-Baja 2.5L DOHC engine
On the 2.0L engine the front (A/F) oxygen sensor is located in the
front section of the exhaust system, just past the crossover pipe. The
rear oxygen sensor is located in the front section of the rear
catalytic converter. On the 2.2L engine the front (A/F) oxygen sensor
is located in the front section of the front catalytic converter. The
rear oxygen sensor is located in the rear section of the rear catalytic
code p 0138 refers to 2 items
1--heated oxygen sensor(HO2S) 2 bank 1--high voltage ==causes --wiring short to positive --HO2S---ECM
2--oxygen sensor (O2S) 2 bank 1--high voltage ===causes wiring short to positive ---ECM
code p 0139 refers to 2 items
1--- heated oxygen sensor (HO2S) 2 bank 1--slow response ===causes --heating inoperative --wiring--ECM
2--oxygen sensor (o2S) 2 bank 1 slow response ===causes --wiring --- O2S
heated oxygen sensors9HO2S) are in the exhaust manifold before the cat converter
Oxygen sensors (O2S) are after the cat converter
it is indicated that the HO2S is faulty-
check the wiring and /or replace both sensors