P0135, P0141 Test Basics O2 Heater Performance Problem (GM 3.8L)

Oxygen Sensor Test Summary

Testing the oxygen sensor is not that hard to do, In my opinion, the hardest part is just getting to it to test it.

So, I'm gonna' offer you some very important safety precautions:

1. Test the oxygen sensor(s) with a cold engine.
   • Whether the oxygen sensors is before or after the catalytic converter, they get HOT if the engine has been running!
   • This extremely hot temperature will cause serious burns on your hands and/or fingers.
   • If you've had your car running, let the engine cool down completely before starting your tests.
2. Use Jack Stands.
   • To get to the O2 sensor after the catalytic converter, you'll have to raise your vehicle.
   • Always use jack stands while working under your vehicle!
   • A jack should never ever be trusted to hold up the vehicle for a long period to time.
3. Use Safety Glasses.
   • Protect your eyes from all of the mud, dirt, etc that will caked up underneath your vehicle (and which you'll disturb when testing the rear (downstream) O2 sensor.

OK, having gotten these safety/precaution suggestions out of the way, in this section I'll briefly describe what the oxygen sensor heater element test (for P0135 and P0141) consists of and then where to find the in-depth, step-by-step, testing tutorials you need.

OK, testing the oxygen sensor's heater element consists of 3 basic tests things. These are:

1. Make sure that the O2 sensor's heater element is getting battery power (10 to 12 Volts DC) with the Key On Engine Off.
2. Make sure that the O2 sensor has a Ground for those 10 to 12 Volts.
3. And last, check the resistance of the O2 sensor's heater element to see if it's fried and registering an ‘open’.

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.

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

• 1994-1996 3.8L Upstream Oxygen Sensor Heater Element Test.
• 1997-2003 3.8L Upstream Oxygen Sensor Heater Element Test.