TEST 1: Checking For 12 Volts (Pink Wire)

P0141, P0161 Downstream O2 Sensor Test (1999-2002 GM 4.8L, 5.3L, 6.0L)

IMPORTANT: To avoid serious/severe burns, perform all tests in this tutorial with a cold engine and/or cold downstream oxygen sensors. If the engine has been running for any amount of time, then let the engine cool down for about 45 minutes to let the O2 sensors cool down too.

The very first thing you and I will do, is to make sure the downstream O2 sensor you're gonna' test is getting power (10 to 12 Volts DC.)

We'll check for this voltage with the Key On Engine Off with either a multimeter or a 12 Volt Test Light

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 downstream oxygen sensor you need to test
    1. Bank 1 Sensor 2 is on the ‘driver’ side of the engine (P0141).
    2. Bank 2 Sensor 2 is on the ‘passenger’ side of the engine (P0161).
    3. 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.
    1. Never trust the jack to hold up the vehicle. Use jack stands!
  3. Disconnect the oxygen sensor from its electrical connector.
  4. Locate the Pink wire of the engine wiring harness oxygen sensor connector.
    1. The letter D will be embossed on the connector.
  5. 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 good, since it confirms that the downstream oxygen (O2) sensor's heater element is being fed with power.

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. I suggest you also 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)

P0141, P0161 Downstream O2 Sensor Test (1999-2002 GM 4.8L, 5.3L, 6.0L)

The post-catalytic converter oxygen sensor's heater element needs Ground to activate. Although it's rare to have a Ground issue, we still need to make sure it's there.

In this section we'll test the Ground circuit with your multimeter in Volts DC mode.

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 (4.8L, 5.3L) circuit wire.
    1. You'll test the wire that is on the engine wiring harness connector side.
    2. This is the Black of the 4 wires.
  3. Place your multimeter in Volts DC mode and:
    1. Connect the red multimeter test lead to battery positive (+) terminal.
    2. Connect the black lead to the C (4.8L, 5.3L) 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- So far so good, since this test result confirms that the Ground wire is OK.

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 Black wire has an ‘open-circuit’ problem.

By an ‘open’, I mean that the wire is cut somewhere between it and its Ground point. To confirm this, you can use a Jumper Wire to Ground this circuit and repeat the test.

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


Cadillac Vehicles:
  • Escalade 5.3L, 6.0L
    • 2002
Chevrolet Vehicles:
  • Avalanche 5.3L
    • 2002
  • Silverado 1500, 2500, 3500 4.8L, 5.3L
    • 1999, 2000, 2001, 2002
  • Suburban 1500, 2500 5.3L
    • 2000, 2001, 2002
Chevrolet Vehicles:
  • Tahoe 4.8L, 5.3L
    • 2000, 2001, 2002
GMC Vehicles:
  • Sierra 1500, 2500, 3500 4.8L, 5.3L, 6.0L
    • 1999, 2000, 2001, 2002
  • Yukon Denali 1500, 2500 4.8L, 5.3L, 6.0L
    • 2000, 2001, 2002