TEST 2: Testing The Heater Element's Resistance
Now that we've made sure that the downstream O2 sensor's heater is gettting power and Ground, in this test section, we're gonna' make sure that its resistance is within specification.
Specifically, what we're looking for is for the rear O2 sensor's heater element's resistance to be within 4 to 20 Ohms Ω.
If it is not within specification, then we can conclude that the downstream O2 sensor is fried and the cause of the P0141 1/2 O2 Sensor Heater Failure trouble code lighting up the check engine light.
NOTE: Just a reminder that the downstream 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 3 and number 4 of the O2 sensor connector itself (not the engine wiring harness O2 connector).
The connector on the O2 sensor itself has male terminals.
Place your multimeter in Ohms mode.
With the multimeter test leads, probe terminals number 3 and number 4 of the O2 sensor itself.
If all is OK, you should see about 4 to 20 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: The O2 heater's resistance is within factory specification. This test result tells you that the rear oxygen sensor's heater is OK.
CASE 2: Your multimeter showed an open circuit (OL). This confirms that the rear O2 sensor's heater element is fried. Replacing the rear O2 sensor with a new one will solve the P0141 trouble code lighting up the check engine light (CEL).
You can correctly conclude that your 2.0L Neon's downstream O2 sensor needs to be replaced with a new one if you have:
- Confirmed that the downstream O2 sensor's heater element is getting power (TEST 1).
- Confirmed that the downstream O2 sensor's heater element is getting Ground (TEST 2).
- In this test you have confirmed that the heater element's resistance is out of specification.
If this info saved the day, buy me a beer!