Troubleshooting a diagnostic trouble code (DTC) P0141: HO2S Heater Circuit Sensor 2 on your 3.8L GM vehicle is not that hard. It's something that the DIY'er can do without too much trouble.
In this tutorial I'll show you the 3 basic multimeter tests you'll need to perform to find out if the rear oxygen sensor's heater is bad and causing the P0141 trouble code.
NOTE: This oxygen sensor is known by several different names:
- Downstream Heated Oxygen (O2) Sensor.
- HO2S Sensor 2.
- Rear Oxygen (O2) Sensor.
- Oxygen Sensor Bank 1 Sensor 2.
- Oxygen Sensor After the Catalytic Converter.
- Post-Catalytic Converter O2 Sensor.
Here are the contents of this tutorial:
- Circuit Descriptions of the Downstream Oxygen Sensor.
- TEST 1: Verifying the Heater Element is Getting Power.
- TEST 2: Verifying the Heater Element is Getting Ground.
- TEST 3: Testing the Heater Element's Resistance.
- Where to Buy the Oxygen Sensor and Save Some $$$.
- More 3.8L GM Diagnostic Tutorials.
FRONT O2 SENSOR TESTS: For the front oxygen sensor heater tests, go here:
- Testing Trouble Code: P0135 (GM 3.8L 1994-1996) (at: troubleshootmyvehicle.com).
- Testing Trouble Code: P0135 (GM 3.8L 1997-2003) (at: troubleshootmyvehicle.com).
Circuit Descriptions of the Downstream Oxygen Sensor
To test the oxygen sensor's heater, we need to know what wires feed it with power and ground (since it's a 4-wire oxygen sensor).
Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for the rear oxygen sensor:
|Downstream Oxygen Sensor Pinout
|A||TAN/WHT||O2 Signal Ground|
|C||BLK (or BLK/WHT)||Heater Ground (-)|
|D||PNK||Heater Power (+)|
TEST 1: Verifying the Heater Element is Getting Power
The rear oxygen sensor, on your 3.8L equipped car, gets power in the form of 12 Volts DC. These 12 Volts are then fed to the rear O2 sensor thru' the pink (PNK) wire of the engine wiring harness rear oxygen sensor connector.
To check for these 12 Volts, we need to do a simple multimeter voltage test.
CAUTION: The oxygen sensor gets and stays very hot even after the engine is off! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions! If you raise your vehicle with a jack, place it on jack stands!
IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the PNK wire of the engine wiring harness sensor connector.
OK, this is what you'll need to do:
Locate the downstream oxygen sensor and disconnect it from its harness connector.
Locate the PNK wire of the engine wiring harness oxygen sensor connector.
With your multimeter in Volts DC mode, probe the PNK with the red multimeter lead.
Ground the black multimeter lead directly on the battery's negative terminal.
With the Key On Engine Off (KOEO), the RED wire should have 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: The PNK wire has 10 to 12 Volts DC- Good, since this confirms that the rear oxygen sensor's heater element is getting power.
The next step is to make check that the black (BLK) wire, of the O2 sensor engine wiring harness connector, is feeding ground to the heater element. For this test, go to TEST 2: Verifying the Heater Element is Getting Ground.
CASE 2: The PNK wire DOES NOT have 10 to 12 Volts DC- Re-check that you're testing the correct wire and that the Key is in the RUN position (but don't crank or start the engine) and re-test.
If you still don't see 10 to 12 Volts DC... then this test result tells you that the downstream oxygen (O2) sensor itself IS NOT BAD... since without power, the heater element won't work.
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.