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

This tutorial will help you test the downstream oxygen sensor's on your 4.8L, 5.3L, or 6.0L Chevy or GMC Pickup or SUV. If this tutorial doesn't cover your specific vehicle, take a look at the index of tutorials here: O2 Sensor Tutorial Index.

When one of the downstream O2 sensors goes BAD, you'll see either a P0141 and/or P0161 diagnostic trouble code lighting up the check engine light on your instrument cluster. Here are the specifics of each trouble code:

  1. P0141: HO2S Heater Performance Bank 1 Sensor 2.
  2. P0161: HO2S Heater Performance Bank 2 Sensor 2.

Remember, these downstream oxygen (O2) sensors are also known as: post catalytic converter oxygen sensors or Rear oxygen sensors.

... Before you start testing/troubleshooting Codes P0141 and/or P0161, I highly recommend that you take a look at the following oxygen sensor test primer:

  1. Testing P0135, P0141, P0155, P0161 O2 Heater Performance Problem.
    1. This article answers a lot of the most common questions like:
      1. Symptoms of a BAD oxygen sensor heater element.
      2. Where are the O2 sensors located?
      3. What tools do I need?
      4. What does the heater inside the oxygen sensor do?

Circuit Descriptions of
the Upstream Oxygen Sensors

P0135, P0155 -Upstream O2 Sensor Test (2003-2005 GM 4.8L, 5.3L, 6.0L) P0135, P0155 -Upstream O2 Sensor Test (2003-2005 GM 4.8L, 5.3L, 6.0L)

Each downstream oxygen sensor has four wires. Each one has a specific job to do, and in this section, we'll take a brief look at those job descriptions.

To get into some more specifics: Each wire is identified by a letter. The four letters used are: A, B, C, and D. The two we need to worry about (to troubleshoot Codes P0141 and P0161), are the circuits C and D.

The really good thing about this letter identification, is that you'll find these letters embossed on the oxygen sensor connector too.

NOTE: In the chance that the color of the wires below don't match what's on the downstream oxygen sensor on your specific vehicle... the info in this tutorial still applies. Why?... Because you can use the letters (A, B, C, and D) embossed on the connectors to identify the circuits.

O2 Bank 1 Sensor 2 Circuits (4.8L, 5.3L, 6.0L)
Pin Wire Color Description
A Tan w/ White stripe HO2S Low Signal
A <-> Tan HO2S Low Signal (Canada built)
B Purple w/ White stripe HO2S High Signal
C Black Heater Element Ground (Chassis Ground)
D Pink Heater Element 12 Volts (O2 sensor fuse)
O2 Bank 2 Sensor 1 Circuits (4.8L, 5.3L, 6.0L)
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple HO2S High Signal
C Black Heater Element Ground (Chassis Ground)
D Pink Heater Element 12 Volts (O2 sensor fuse)

TEST INFO: The Basics of
Testing the Oxygen Sensor Heater Element

IMPORTANT: Perform the downstream oxygen (O2) sensor tests (in this tutorial) with a completely cold engine. If the engine has been running... the Upstream and downstream O2 sensors will be EXTREMELY HOT.

If the engine is hot, let it cool down completely. This will give the O2 sensor enough time to cool down too... or you run the risk of severe burns from the exhaust pipe or the O2 sensors themselves!

OK, keeping the above safety precautions in mind.... in a nutshell, we'll start out our P0141 and/or P0161 troubleshooting tests by making sure that the oxygen sensor's heater element is getting both voltage and ground.

With the Key On but Engine Off, the O2 sensor should get 10 to 12 Volts from an oxygen sensor fuse. ground is provided internally by the PCM.

Here are some more specifics:

  1. Power is provided by the D circuit wire.
    1. This wire will be the Pink wire of the O2 sensor connector (engine wiring harness side).
  2. ground is provided by the C wire (4.8L, 5.3L) or the E wire (6.0L).
    1. This is the Black wire of the O2 sensor connector (engine wiring harness side).

If it turns out that the downstream O2 sensor's heater element is missing power or ground, well... you found the causes of the P0141 and/or P0161 trouble codes.

Now, if both power (10 to 12 Volts DC) and ground are present, then the next step, is to measure the resistance (with a multimeter) of the heater element inside the oxygen (O2) sensor to see if it's fried or not.

Alright, I'll stop yakking and we'll get testing DTC's P0141 and/or P0161 in the next few pages are the step-by-step testing instructions you'll need to get to the bottom of the problem.