TEST 2: Testing The Heater Element's Resistance
Now that you've checked/confirmed that power (12 Volts) and Ground is reaching the heater, the last thing we need to do is to measure it's resistance.
If the resistance is out of specification and you've verified that power and Ground are reaching the rear O2 sensor's heater, then you can conclude that it's fried and the whole sensor needs to be replaced.
NOTE: Just a reminder that the oxygen sensor has to be completely cold before proceeding with this test since the manual calls for the O2 sensor to be at room temperature for the resistance test.
OK, this is what you need to do:
Locate the O2 sensor terminals number 1 and number 2 of the O2 sensor connector itself (not the engine wiring harness O2 connector).
With your multimeter in Ohms mode, probe terminals number 1 and number 2 of the O2 sensor itself.
If all is OK, you should see about 11 to 16 Ωs on your multimeter.
If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL) or a number over 10 K Ωs.
Let's take a look at your test results:
CASE 1: Your Corolla's rear O2 heater's resistance is within factory specification. This test result tells you that the rear O2's heater is OK.
CASE 2: Your multimeter showed an open circuit (OL). This confirms that the rear O2's heater element, on your Corolla, is fried. Replacing the rear oxygen sensor with a new one will solve the P0141 trouble code lighting up the check engine light (CEL).
Taking into account that you have:
- In TEST 1 you verified power and Ground is reaching the sensor's heater.
- In this test you have confirmed that the heater element's resistance is out of specification.
... You can correctly conclude that your 1.8L Toyota Corolla downstream O2 sensor needs to be replaced with a new one.
Where To Buy The Oxygen Sensor And Save Some $$$
If the rear oxygen sensor's heater is fried, the following links will help you to comparison shop and save money on a new oxygen sensor.
NOTE: If you're not sure if the above O2 sensor fit your particular 1.8L Toyota Corolla don't worry, once you get to the site, they'll make sure the sensor is the right one, if not, they'll find you the right one.
More 1.8L Toyota Diagnostic Tutorials
You can find a complete list of 1.8L Toyota tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The TP Sensor (1998-2002 1.8L Toyota).
- How To Test The Fuel Injectors (Toyota 1.8L).
- Diagnosing a Toyota Corolla Misfire Case Study (Toyota 1.8L).
- How To Test Engine Compression (Toyota 1.8L).
- How To Test For A Blown Head Gasket (Toyota 1.8L).
If this info saved the day, buy me a beer!