The 2001 V6 engine has one main catalytic converter and two smaller "PUP" converters.


The main converter is divided into two "bricks." The first brink is a REDUCTION catalyst. It converts nitrogen oxides (NOX) into nitrogen, carbon dioxide and water vapor.


The second brick is the OXIDATION catalyst. It converts carbon monoxide into carbon dioxide and water vapor.


Catalytic converters do not become fully effective until they reach a temperature of 400° to 600° F. As a result vehicles emit most of their total pollution during the first five minutes of engine
operation. To meet California's Low Emissions Vehicle (LEV) standard, engineers added small catalytic (PUP) converters which heat up faster on vehicle start up.


Catalytic converters work best when the air/fuel ratio is held at 14.7:1. The PCM
uses feedback from the oxygen sensors to maintain that ratio but until the O2
sensors warm up the computer uses information stored in memory to guess at
an appropriate amount of fuel to add. This is called "open loop" operation.
Once the O2 sensors reach their operating temperature, the engine goes into
"closed loop" operation.


If the computer sees that the PUP converter is not doing its job, it will set the DTC
P0420 for the driver's side PUP or P0430 for the passenger side. The main cause
of catalytic converter failure is engine misfires. When a cylinder misfires unburned
gasoline is dumped into the hot converter where it ignites. That will melt the brick
inside the converter. The crankshaft position sensor can detect misfires as small
variations in engine speed. Some cars will flash the "check engine" light to get
your attention. Some cars will shut off the injector to the misfiring cylinder in an
attempt to save the converter. I'm not sure how the Tracker handles misfires
other than to record them.


The 2001 Tracker use a "planar" type oxygen sensor.


The PCM feeds a reference voltage to the oxygen sensor resistor. The change in O2 resistance is detectable as a change
in current inside the PCM. The full-size O2 schematic is downloadable at https://www.dropbox.com/s/3rxlu8bp92...matic.jpg?dl=0


This is a plot of Sensor 1 and Sensor 2 on the Bank 1 PUP of my Tracker. The straight line
of Sensor 2 indicates the cat is operating normally. The high and low peaks of Sensor 1 are
caused by small changes to the pulse width of the fuel injector signal. If the the O2 sensor
detects a "rich" condition, the PCM reduces the injector pulse width producing a "lean"
condition. When the O2 sensor detects the lean condition, the PCM responds by increasing
injector pulse with a little. By constantly bouncing between "rich" and "lean" the PCM is able
to maintain an air/fuel ratio right around 14.7:1.

 

Have have the same question but got a 98 chevy c1500 single v6..