Oxygen Sensor Test Summary

Testing the upstream or downstream oxygen sensors, to see if they have a fried internal heater element is easy... but you have to take two very important safety precautions:

  1. Test them with a cold engine.
    1. The oxygen sensors absorb ALL of the exhaust pipe's heat and they get HOT!
    2. This extreme temperature can cause serious burns on your hands and/or fingers.
    3. If you have had the engine running for any amount of time, then the O2 sensors are HOT, so let the engine cool down for at least 45 minutes (or more) to let the upstream and downstream oxygen sensors cool down.
  2. Use jack stands.
    1. To get to the upstream or downstream O2 sensors, you'll have to raise your vehicle.
    2. Never trust the jack to keep the vehicle up in the air (while you're underneath it).
    3. Always use jack stands!
  3. Use safety glasses.
    1. The underneath of your Chevy or GMC pickup, van or SUV will be heavy with dirt, mud, etc... use safety glasses.

OK, having gotten these safety/precaution suggestions out of the way.... there are three specific things you need to do, to test the oxygen sensor heater element and thus condemn the O2 sensor as BAD or not. These are:

  1. Make sure that the heater element is getting battery power (10 to 12 Volts DC).
  2. Make sure that the PCM is supplying a ground to the heater element.
  3. And last... check the resistance of the heater element to see if it's fried and registering an ‘open’ short.

All in all, testing the oxygen sensor heater element (inside the O2 sensor itself) is a pretty easy test.

What complicates things a little, is just knowing which wires are the ones that supply this battery power and ground... since each oxygen sensor has 4 wires coming out of it.

O2 Sensor Tutorial Index

To further help you in effectively diagnosing each O2 sensor (and trouble codes: P0135, P0141, P0155, and P0161), here's a list of articles that will help you to diagnose these codes in a step-by-step manner:

Upstream Oxygen Sensor Tests (P0135, P0155):

  1. 1999-2002 4.8L, 5.3L, 6.0L Upstream Oxygen Sensor Heater Element Test.
  2. 2003-2005 4.8L, 5.3L, 6.0L Upstream Oxygen Sensor Heater Element Test.
  3. 2006-2010 4.8L, 5.3L, 6.0L Upstream Oxygen Sensor Heater Element Test.

Downstream Oxygen Sensor Tests (P0141, P0161):

  1. 1999-2002 4.8L, 5.3L, 6.0L Downstream Oxygen Sensor Heater Element Test.
  2. 2003-2005 4.8L, 5.3L, 6.0L Downstream Oxygen Sensor Heater Element Test.