How To Test The Upstream Oxygen Sensor (2006-2009 GM 4.8L, 5.3L, 6.0L)

With the help from this tutorial, you be able to test the oxygen sensor to see if its heater element is really fried, and thus causing the P0135 or P0155 to light up your check engine light. In case this tutorial doesn't cover your specific vehicle, take a look at the index of tutorials here: O2 Sensor Tutorial Index.

This is a pretty simple test that you can do with a multimeter and I'll show you how to do it in a step-by-step way.

NOTE: Your Chevy (or GMC) pickup or SUV will have one of two types of upstream oxygen (O2) sensors for Bank 1 and Bank 2. What's the difference?... you might ask... well, its the type of connector used.

Using the photo below, if your Chevy or GMC pickup or SUV has a 4.8L or a 5.3L V8, the O2 sensor connector will look like the one labeled with number 1 or number 3.

If your GMC (or Chevy) pickup, van or SUV has the 6.0L V8 engine, then the upstream oxygen sensors for Bank 1 and Bank 2 will have the connector labeled with the number 2 in the photo below.

This article covers testing all of them...

... Before you start testing/troubleshooting codes P0135 and/or P0155, I 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 (2006-2009 GM 4.8L, 5.3L, 6.0L) P0135, P0155 -Upstream O2 Sensor Test (2006-2009 GM 4.8L, 5.3L, 6.0L) P0135, P0155 -Upstream O2 Sensor Test (2006-2009 GM 4.8L, 5.3L, 6.0L)

As I mentioned at the beginning of this tutorial, GM uses one of three different types of upstream oxygen sensors... and these can be told apart by their connectors.

In the photos I'm using in this article, I'm labeling the oxygen sensors used on the 4.8L and 5.3L V8 engines with the number 1 and number 3. The oxygen sensor type that's used on the 6.0L V8, I'm identifying it with the number 2.

This tutorial covers testing all three types and in the circuit descriptions below I've taken this into account.

O2 Bank 1 Sensor 1 Circuits (4.8L, 5.3L)
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple w/ White stripe HO2S High Signal
C Black w/ White stripe Heater Element Ground (Provide by PCM)
D Pink Heater Element 12 Volts (O2 sensor fuse)
O2 Bank 2 Sensor 1 Circuits (4.8L, 5.3L)
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple HO2S High Signal
C Light Green Heater Element Ground (Provide by PCM)
D Pink Heater Element 12 Volts (O2 sensor fuse)
O2 Bank 1 Sensor 1 Circuits (6.0L)
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple w/ White stripe HO2S High Signal
C --- Empty
D Pink Heater Element 12 Volts (O2 sensor fuse)
E Black w/ White stripe Heater Element Ground (Provided by PCM)
O2 Bank 2 Sensor 1 Circuits (6.0L)
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple HO2S High Signal
C --- Empty
D Pink Heater Element 12 Volts (O2 sensor fuse)
E Light Green Heater Element Ground (Provided by PCM)

TEST INFO: The Basics Of Testing The Oxygen Sensor Heater Element

IMPORTANT: Since the oxygen sensors are connected to the exhaust pipe, they get VERY HOT with the engine running and may take a while to cool down! The test instructions, in this tutorial, call for all of the tests to be done with a cold engine and cold O2 sensors.

If the engine has been running, let it it cool down for at least 45 minutes, before attempting the tests in this tutorial or you run the risk of severe burns from the hot exhaust pipe and/or oxygen sensors.

OK, keeping the above safety precautions in mind.... in a nutshell, the very first thing that has to be checked (and confirmed) is if the oxygen sensor's heater element is getting juice and ground.

This power (juice), comes in the form of 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 one, regardless of the type of O2 sensor GM has installed on your vehicle.
  2. ground is provided by the C wire (4.8L, 5.3L) or the E wire (6.0L).
    1. This wire will be one of several colors, depending if the O2 sensor is on Bank 1 or Bank 2 and engine size. Consult the Circuit Descriptions charts above to make sure.

If any of these two is missing (power or ground), then you have eliminated the O2 sensor as BAD. Why? Well, because without power or ground, the O2 sensor's heater element won't function and the PCM will find out (and will illuminate the check engine light with codes: P0135 and/or P0155).

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.

As you can see, testing DTC's P0135 and/or P0155 is not hard to do at all.... OK, in the next few pages are the step-by-step testing instructions you'll need to get to the bottom of the problem.