Kwiksen Heated Universal 4pcs Upstream Downstream O2 Oxygen Sensor 234-4127 234-4401 Replacement for Ford Explorer 2004 2005 2006 2007 2008 2009 2010

• The following information is for instructional and guidance reference only. We try and make them as accurate as we can.
• If Check Engine Light is on or an OBDII Trouble/Fault code occurs after installation, check the sensor with a voltmeter as below. If the sensor is good, further diagnosis is required. There're many different codes for specific functional failures, which are NOT necessarily relevant to the sensor. Find out what the Code means before leaving any feedbacks.
• Items that have been installed, altered or contaminated are non-returnable. ONLY a defective sensor after tested by a voltmeter is applied to manufacturer warranty. 
• 20% restocking fee is required if buyer bought wrong items due to not paying attention to fitment information and ask for return.
• The Price, Quality & Funcitonality of the O2 Sensor is fully covered under our warranty & return policy. However, refund for any labor cost, expense in a dealer shop or damage due to wrong installation is NOT covered.

Q: How do I know the O2 sensor is good or not? (Online Video)

A: The only way to know if the O2 sensor is functioning normally is to check its responsiveness to changes in the air/fuel mixture, by Voltage Measurement or Waveform Simulation.

Use a 10-megaohm digital voltmeter. Hook up the voltmeter's red probe to the sensor's signal wire and the black probe to engine ground. (Use back probe method, DO NOT pierce the wire.) For a good sensor, voltage should fluctuate constantly between 0.1 and 0.9 volts after starting the engine for 2 or 3 minutes.

Please take a video clip of the voltmeter and contact us if our sensor:

• Goes above range between 0.1 and 0.9 volt
• Remains below 0.5 volts
• Stays fixed at a particular voltage

You're free to choose replacement or refund if our sensor fails to work, in this case.