The rear oxygen sensor on your 2.0L Neon is equipped with an internal heater. This heater gets it to reach its operational temperature fast when you start up the engine. It also keeps it activated during all engine operating conditions. But, sooner or later, this oxygen sensor heater will fail.
When it fails, your Neon's fuel injection computer will light up the check engine light with a trouble code P0141: 1/2 O2 Sensor Heater Failure. 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:
If you need to test the upstream (front) oxygen sensor heater or a P0135 trouble code, the following tutorial will help: Front O2 Sensor Heater Test -P0135 (1997-1999 2.0L Neon)
Circuit Descriptions Of The Downstream Oxygen Sensor
As you've already take a look at the downstream oxygen sensor, you're aware that it has 4 wires sticking out of it's connector. 2 wires are for actual oxygen sensing part of the sensor assembly. The other 2 are to supply the heater with power and ground.
For our testing purposes, it's important to note that the connector on the oxygen sensor itself has female terminals. The oxygen sensor's engine wiring harness connector has male terminals (see the photo above).
Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for sensor HO2S-11:
|HO2S 1/2 Pinout
1997-1999 2.0L Neon
|1||DK GRN/ORG||Heater Power (+)|
|2||BLK||Heater Ground (-)|
|3||BLK/LT BLU||O2 Signal Ground|
TEST 1: Verifying The Heater Element Is Getting Power And Ground
The downstream oxygen sensor's heater needs both power and ground to activate. Power comes in the form of 12 Volts DC and in this first test section we're gonna' make sure it's getting them both.
Checking for power and ground is a pretty easy thing to do and in the test instruction below I'll explain how.
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 tell them apart because the O2 sensor's engine wiring harness connector has the male 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: Power and ground and being fed to the downstream O2 sensor- 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: Power IS NOT being fed to the downstream O2 sensor- 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: Ground IS NOT being fed to the downstream O2 sensor- 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.