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

TEST 3: O2 Heater Resistance Test

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OK, we're almost done. The very last test (3 of 3), is to see if the heater element inside the Post Catalytic Conveter oxygen sensor is fried or not.

So far in your diagnostic, you've checked and confirmed:

• The downstream O2 sensor is being fed with 10 to 12 Volts (TEST 1).
• That it also has a good path to Ground (TEST 2).

OK, this is what you need to do:

1. Disconnect the Drownstream oxygen sensor from the engine wiring harness connector (if it isn't already from the previous tests).
   • NOTE: The O2 sensor must be disconnected from the vehicle's connector for this test!
2. Locate the O2 sensor wires that correspond to:
   • The circuit C and D.
   • Both of these letters should be embossed on the O2 sensor's connector to aid you in further identifying the circuits you need to test.
   • 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. With your multimeter in Ohms mode, probe the terminals that correspond to the letters C and D of the O2 sensor connector.
   • NOTE: Remember, you're testing the oxygen sensor itself.
   • If all is OK, you should see about 5 to 16 Ω (Ohms).
   • If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL).

Let's take a look at your test results:

CASE 1: The heater element resistance was within specification. This tells you that the heater element within the oxygen sensor is OK.

CASE 2: The heater element resistance WAS NOT within specification (multimeter shows OL). Repeat the test several times to make sure of your test result.

If your multimeter still registers OL, then this test result tells you that you need a new downstream oxygen sensor. Replace the downstream oxygen sensor, this bad boy is fried.

Depending on what downstream oxygen sensor you're testing (either Bank 1 Sensor 2 or Bank 2 Sensor 2), replacing the oxygen sensor will solve the P0141 or P0161 diagnostic trouble code.

Here's why: You have so far:

• Done TEST 1, and you've verified that the post catalytic converter O2 sensor you're testing is getting juice (10 to 12 Volts) with the Key On Engine Off.
• Done TEST 2, and you have confirmed that the PCM is providing a Ground for the O2 sensor's heater element.
• In this test, you have confirmed that the O2 sensor's heater element is fried internally.

So, keeping in mind all of the above, you can replace the O2 sensor with confidence!

If this info saved the day, buy me a beer!