How to replace a oxygen sensor upstream ,Mazda Protégé 5 2002

Oxygen Sensor Replacement

Trick: Take a small flashlight and figure out how the oxygen sensor's 4-wire pigtail connector comes apart--don't force it. Frequently, the trick is to gently separate the connector from the bayonet mount first; then, it easily comes apart or it's apparent how it unlocks. Connectors can be tricky and give some do-it-yourselfers a fit.


Remove heat shield, spray old oxygen sensor with PB Blaster or Kroil (let it sit for a while), spray with PB Blaster or Kroil again, warm-up car for several minutes, and use a 15-inch breaker bar on the end of a 22 mm oxygen sensor socket to remove sensor. Afterwards, clean threads thoroughly with brake cleaner, allow to sit for quite a while and "air-out," and install new oxygen sensor with anti-seize compound. Good cleaning technique is a must. Tighten to 33 lb.-ft. or 4.5 kg-m. Lightly coat heat shield bolts with anti-seize compound, before reinstalling the heat shield.

I am not a fan of universal oxygen sensors or those made by Bosch. I recommend Denso sensors. Over time, you want the best sensor or you will pay for it in poor gas mileage and performance. Oxygen sensors are EXTREMELY sensitive to anything, particularly silicone spray, RTV sealers, WD-40, or any oil on the pigtail connector. Don't even use non-chlorinating brake cleaner or electrical contact cleaner on oxygen sensor connectors. NEVER use any of these products around the oxygen sensor or pigtail connector. If you do, the ECM will keep throwing a code forever, once the engine warms up and is out of "open loop" mode. Remove pigtail connector and gently dress the male and female connectors with jeweler files, if you suspect any contamination.

After replacing the oxygen sensor, clear the Check Engine Light by using a code reader or scan tool to reset the ECM.