Engine Exhaust OxygenSensors

This 2001 Ford Explorer Sport Trac & V6~4.0L~SOHC engine has 3 OxygenSensors; they're also known as HEGO\HeatedExhaustGasOxygen, H02\HeatedOxygen, Lambda\NarrowBand Sensors; as located below.

Links To Related Info
Thanks go to the brave souls who've preceded me in similar adventures & freely shared their experience:
 * https://web.archive.org/web/20170701123657if_/http://www.partsgeek.com/mmparts/the_ultimate_guide_to_the_oxygen_sensor_for_dummies.html
 * https://web.archive.org/web/20200907142452if_/http://secure.lambdapower.co.uk/TechNotes/Tech-1.asp
 * https://web.archive.org/web/20200907135224if_/http://www.bosch.com/stories/40-years-of-bosch-lambda-sensor
 * https://web.archive.org/web/20200907151720if_/https://www.freeasestudyguides.com/heated-oxygen-sensor.html
 * https://web.archive.org/web/20200907151127if_/http://www.fuelinjectedford.com/page31.html
 * https://web.archive.org/web/20130626102106if_/http://www.motorcraftservice.com/vdirs/diagnostics/pdf/obdsm109.pdf#page=24
 * https://web.archive.org/web/20200822182035if_/http://troubleshootmyvehicle.com/ford/4.0L/testing-the-oxygen-sensors-1
 * https://web.archive.org/web/20200822182408if_/http://troubleshootmyvehicle.com/ford/4.0L/testing-the-oxygen-sensors-2
 * https://web.archive.org/web/20200822182457if_/http://troubleshootmyvehicle.com/ford/4.0L/testing-the-oxygen-sensors-3
 * https://web.archive.org/web/20200910195723if_/https://www.ranger-forums.com/4-0l-ohv-sohc-v6-tech-33/how-many-o2-sensors-137557 OxygenSensor Locations
 * https://www.ranger-forums.com/general-ford-ranger-discussion-15/downstream-o2-sensor-voltage-164365 OxygenSensor Diagnosis
 * https://youtu.be/afio03Sv_MU?t=0 OxygenSensor12@RearTailPipe Diagnos
 * https://youtu.be/QiA8uksEYHo?t=25 OxygenSensors Replace
 * https://youtu.be/9QzD8_srbSM?t=1 OxygenSensors Replace
 * https://youtu.be/7Rtw8jI9quA?t=40 OxygenSensor11@RghtManifold Replace
 * https://youtu.be/3reiaSERIXY?t=162 OxygenSensor11@RghtManifold Replace
 * https://youtu.be/BVUzDz6i_bw?t=24 OxygenSensor12@RearTailPipe Replace
 * https://web.archive.org/web/20200907182450if_/https://www.explorerforum.com/forums/threads/how-to-install-new-upstream-o2-sensors.282979 OxygenSensor11+21@Rght+LeftManifolds Replace
 * https://www.boschautoparts.com/en/auto/oxygen-sensors/premium-oxygen-sensors?partId=13117 OxygenSensor11+21@Rght+LeftManifold Bosch# 13117
 * https://www.boschautoparts.com/en/auto/oxygen-sensors/premium-oxygen-sensors?partId=15716 OxygenSensor12@RearTailPipe Bosch# 15716
 * https://web.archive.org/web/20201113152331if_/https://images.carid.com/walker/items/schemes/13-03880.jpg ExhaustSystem PartsList Walker
 * https://www.google.ca/search?q=%2B%22walker+exhaust+50202%22&tbm=isch&ved=2ahUKEwi3vKPu6P_sAhVBUM0KHTvNA4kQ2-cCegQIABAA&oq=%2B%22walker+exhaust+50202%22&gs_lcp=CgNpbWcQA1DpxwFYu_gBYK79AWgBcAB4AIABtgKIAYMpkgEIMC4yNS4zLjGYAQCgAQGqAQtnd3Mtd2l6LWltZ8ABAQ&sclient=img&ei=_aOuX_fJFsGgtQa7mo_ICA CatConvertors UpStream.47StateCompliant Walker# 50202
 * https://www.google.ca/search?q=DEC+FOR9T20432&tbm=isch&ved=2ahUKEwiCxont9v_sAhX5Ap0JHdkPAhEQ2-cCegQIABAA&oq=DEC+FOR9T20432&gs_lcp=CgNpbWcQA1D-4BdYp5EYYNSVGGgBcAB4A4AB3AKIAeUYkgEIMC4xOC4yLjGYAQCgAQGqAQtnd3Mtd2l6LWltZ7ABAMABAQ&sclient=img&ei=qLKuX4LSOfmF9PwP2Z-IiAE&bih=612&biw=1366 CatConvertors UpStream.50StateCompliant DEC# for9t20432
 * https://www.google.ca/search?q=walker+exhaust+53500&tbm=isch&ved=2ahUKEwjzpceq6__sAhV0A50JHbwfBLAQ2-cCegQIABAA&oq=walker+exhaust+53500&gs_lcp=CgNpbWcQAzoECAAQGFCDwCRYiNMkYOrfJGgAcAB4AIABhgGIAckGkgEDMy41mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=lKauX_OLKPSG9PwPvL-QgAs&bih=612&biw=1366 CatConvertors DnStream.47StateCompliant Walker# 53500
 * https://www.google.ca/search?q=Bosal+079-4172&tbm=isch&ved=2ahUKEwjQlJq67v_sAhUQX80KHU9eCsIQ2-cCegQIABAA&oq=Bosal+079-4172&gs_lcp=CgNpbWcQA1CDGVjNJWCLKmgAcAB4AIABqgGIAfIFkgEDMC42mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=2qmuX9C_L5C-tQbPvKmQDA&bih=612&biw=1366 CatConvertors DnStream.47StateCompliant Bosal# 719-4172
 * https://www.google.ca/search?q=DEC+FOR920586&tbm=isch&ved=2ahUKEwjwvc2r-P_sAhUJBs0KHUvgBqkQ2-cCegQIABAA&oq=DEC+FOR920586&gs_lcp=CgNpbWcQAzoCCAA6BQgAELEDOgQIABBDOggIABCxAxCDAVD0nhZYiLQWYPbAFmgAcAB4AIABmAGIAf8KkgEEMC4xMZgBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=OLSuX_DBH4mMtAbLwJvICg&bih=612&biw=1366 CatConvertors DnStream.50StateCompliant DEC# for920586
 * https://www.therangerstation.com/forums/index.php?threads/diagnosis-of-a-clogged-catalytic-converter.188268 CatConvertors Clog
 * https://www.google.ca/search?q=walker+exhaust+53500&tbm=isch&ved=2ahUKEwjzpceq6__sAhV0A50JHbwfBLAQ2-cCegQIABAA&oq=walker+exhaust+53500&gs_lcp=CgNpbWcQAzoECAAQGFCDwCRYiNMkYOrfJGgAcAB4AIABhgGIAckGkgEDMy41mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=lKauX_OLKPSG9PwPvL-QgAs&bih=612&biw=1366 CatConvertors DnStream.47StateCompliant Walker# 53500
 * https://www.google.ca/search?q=Bosal+079-4172&tbm=isch&ved=2ahUKEwjQlJq67v_sAhUQX80KHU9eCsIQ2-cCegQIABAA&oq=Bosal+079-4172&gs_lcp=CgNpbWcQA1CDGVjNJWCLKmgAcAB4AIABqgGIAfIFkgEDMC42mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=2qmuX9C_L5C-tQbPvKmQDA&bih=612&biw=1366 CatConvertors DnStream.47StateCompliant Bosal# 719-4172
 * https://www.google.ca/search?q=DEC+FOR920586&tbm=isch&ved=2ahUKEwjwvc2r-P_sAhUJBs0KHUvgBqkQ2-cCegQIABAA&oq=DEC+FOR920586&gs_lcp=CgNpbWcQAzoCCAA6BQgAELEDOgQIABBDOggIABCxAxCDAVD0nhZYiLQWYPbAFmgAcAB4AIABmAGIAf8KkgEEMC4xMZgBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=OLSuX_DBH4mMtAbLwJvICg&bih=612&biw=1366 CatConvertors DnStream.50StateCompliant DEC# for920586
 * https://www.therangerstation.com/forums/index.php?threads/diagnosis-of-a-clogged-catalytic-converter.188268 CatConvertors Clog