P0141, P0161 -Downstream O2 Sensor Test (2003-2005 GM 5.3L, 6.0L)

TEST 1: Checking For 12 Volts (Pink Wire)

IMPORTANT: Remember, if the engine is hot or you've just turned it off, the rear O2 sensor are extremely hot! Let the engine cool down for about 45 minutes at least to give the exhaust pipe and O2 sensors a chande to cool down.

OK, to get our testing underway, what you'll need to do first is to make sure the downstream O2 sensor you're gonna' test is getting power (10 to 12 Volts DC.)

Power (the 10 to 12 Volts) are only delivered to the post catalytic converter O2 sensors with the key in the ON (RUN) position. You can use either a multimeter or a 12 Volt Test Light

Just to make sure that you're getting the right amount of voltage, I recommend using a multimeter. If you don't have one or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing at: easyautodiagnostics.com).

OK, to get our P0141/P0161 DTC troubleshooting under way, this is what you need to do:

1. Locate the upstream oxygen sensor you need to test
   • Bank 1 Sensor 2 is on the ‘driver’ side of the engine (P0141).
   • Bank 2 Sensor 2 is on the ‘passenger’ side of the engine (P0161).
   • If you need more specifics on the location of these downstream O2 sensors, take a look at this primer: How To Locate The Oxygen Sensors.
2. Raise the vehicle and support it on Jack Stands (if applicable) to access the oxygen (O2) sensors.
   • Never trust the jack to hold up the vehicle. Use Jack Stands!
3. Disconnect the oxygen sensor from its electrical connector.
4. Identify the style of oxygen sensor connector using the illustrations in the image viewer above.
5. Locate the Pink wire of the engine wiring harness oxygen sensor connector.
   • The letter D will be embossed on the connector.
6. With the Key On Engine Off, this wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter recorded 10 to 12 Volts DC. This is the correct and expected result and let's you know that the heater element inside the downstream O2 sensor you're testing is getting juice (power).

If you've read the O2 sensor primer (found here: What Does The Heater Inside The Oxygen Sensor Do?), you know that the O2 sensor's heater element needs a Ground to activate.

So the next step is to make sure that the downstream oxygen sensor's heater element is being fed with Ground on the C circuit wire. For this test, go to: TEST 2.

CASE 2: Your Multimeter DID NOT record the indicated voltage- This usually means that the O2 sensor fuse is blown.

Check the oxygen sensor fuse and if blown, replace and re-test. Although it's beyond the scope of this tutorial to find out why this fuse is blown, the usual cause is that the O2 sensor's wiring has rubbed up against the hot exhaust pipe and has shorted to Ground.

If you do find that the O2 sensor fuse is blown, check the wiring for burned thru' spots. What usually happens is that the oxygen (O2) sensor's wiring ends up either rubbing against a hard edge and shorts out or ends up touching the hot exhaust pipe and the pipe burns thru' the wire's insulation.

Also, I suggest you perform TEST 3, to make sure that the heater element inside the O2 sensor has not shorted to Ground internally.

TEST 2: Checking Ground (Circuit C Wire)

The second test (of 3), is to make sure that the PCM is activating the heater element by providing it with Ground.

This Ground is provided by the PCM internally, so you need to be careful NOT to short this wire to power (battery voltage) or you run the risk of frying the PCM (Powertrain Control Module = Fuel Injection Computer).

This is what you'll need to do:

1. Disconnect the rear oxygen sensor (if it isn't already from TEST 1).
2. Locate the circuit C circuit wire.
   • You'll test the wire that is on the engine wiring harness connector side.
   • This is usually the Black of the 4 wires.
   • Remember: Identify the style of oxygen sensor connector using the illustrations in the image viewer above so that you'll test the correct circuit.
3. Place your multimeter in Volts DC mode and:
   • Connect the Red Multimeter Lead to Battery Positive (+) Terminal.
   • Connect the Black lead to the C circuit wire of the engine wiring harness connector side.
4. With the Key On Engine Off, this wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: The multimeter registered 10 to 12 Volts DC. This is good, since this test proves that the PCM is providing the Ground the O2 sensor's heater element needs to activate.

Now that we know that the post-catalytic converter O2 sensor's heater element is getting voltage and Ground, the next step is to test the heater element, inside the O2 sensor, itself. This is a simple resistance done with your multimeter. For this test, go to: TEST 3.

CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. Re-check all of your connections and make sure you're testing the correct wire.

If your multimeter still does not indicate the 10 to 12 Volts DC, then the D circuit wire has an ‘open-circuit’ problem somewhere between the O2 sensor connector and the PCM or the PCM is fried (although this is very rare).

Repairing this Ground issue will solve the P0141 and/or P0161 issue you're having with your GM pickup or SUV.