The rear oxygen sensor on your 2.0L Neon is equipped with an internal heater. This heater helps the oxygen sensor activate faster and stay activated. Unfortunately, this heater doesn't last forever.
When it fails, you'll see a trouble code P0141 1/2 O2 Sensor Heater Failure lighting up the check engine light on your Neon's instrument cluster. The good news is that the rear O2 sensor's heater can be tested in 3 simple tests. All you'll need is a multimeter and in this tutorial I'll show you how.
Contents of this tutorial:
You can find this tutorial in Spanish here: Pruebas Del Calentador Del Sensor De Oxígeno Trasero -P0141 (1995-1996 2.0L Neon) (at: autotecnico-online.com).
Circuit Descriptions Of The Downstream Oxygen Sensor
For the oxygen sensor to activate and stay activated, it needs to get hot and stay hot. To be a bit more specific, it needs to reach a temperature of about 600°F + to activate. The hot exhaust stream the O2 sensor is exposed to isn't hot enough to get it to its operating temp fast enough. Also, when the engine idles, the exhaust stream starts to cool. This cooling down, of the exhaust stream, causes the O2 sensor to stop working.
This is where the oxygen sensor's internal heater saves the day since, at engine start, it gets the O2 sensor to reach its operating temperature fast. It also maintains the O2 sensor at its operating temperature under all engine operating conditions. This means that your Neon is polluting less and maximizing gas mileage through out the entire time the engine is running.
As you're probably already aware, there are 4 wires sticking out the oxygen sensor. 2 wires are for actual oxygen sensing part of the sensor assembly. The other 2 are to supply the heater with power and Ground.
Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for sensor HO2S-12:
|HO2S 1/2 Pinout
1995-1996 2.0L Neon
|1||BLK/LT BLU||O2 Signal Ground|
|3||BLK||Heater Ground (-)|
|4||DK GRN/ORG||Heater Power (+)|
TEST 1: Verifying The Heater Element Is Getting Power And Ground
Making sure that the oxygen sensor's heater is getting power and Ground is the first thing that we're gonna' do to find out if it's bad (or not).
Checking for power is a pretty easy affair since we can do a simple multimeter voltage test.
CAUTION: Perform all tests with a completely cold engine! The O2 sensor gets and stays very hot! Also, if you raise your vehicle with a jack, place it on jack stands.
NOTE: This test is done on the O2 sensor's engine wiring harness connector. You can easily identify this connector because it has the female terminals and its wires are color coded.
OK, these are the test steps:
Verify that the dark green with orange stripe (DK GRN/ORG) wire has 10 to 12 Volts DC with the key on but engine off.
Connect the red multimeter test lead (using the appropriate tool) to the DK GRN/ORG wire. Connect the black multimeter test lead to the negative battery terminal.
Your multimeter should read 10 to 12 Volts DC.
Verify that the black (BLK) wire has Ground with the key on but engine off.
Connect the black multimeter test lead (using the appropriate tool) to the BLK wire. Connect the red multimeter test lead to the positive battery terminal.
Your multimeter should read 12 Volts DC.
Let's take a look at your test results:
CASE 1: Your test result shows that the rear O2 sensor's heater is getting power and Ground. This is the correct and expected test result.
Now, we need to make sure that the heater's resistance is within specification. For this test, go to: TEST 2: Testing The Heater Element's Resistance.
CASE 2: Your test result shows that the rear O2 sensor's heater IS NOT getting power. Re-check that you're testing the correct wire and repeat the test.
If your multimeter still does not register 10 to 12 Volts DC, then we can conclude that the oxygen sensor's heater isn't working due to a lack of power.
Although it's beyond the scope of this article, the next step is to find out why this battery power is missing using a wiring diagram.
CASE 3: Your test result shows that the rear O2 sensor's heater IS NOT getting Ground. Re-check that you're testing the correct wire and repeat the test.
If your multimeter still does not register 10 to 12 Volts DC, then we can conclude that the oxygen sensor's heater isn't working due to a lack of Ground.
Although it's beyond the scope of this article, the next step is to find out why this Ground is missing using a wiring diagram.