P0135, P0155 -Upstream O2 Sensor Test (1999-2002 GM 4.8L, 5.3L, 6.0L)

P0135, P0155 -Upstream O2 Sensor Test (1999-2002 GM 4.8L, 5.3L, 6.0L)

This tutorial will help you to test diagnostic trouble codes P0135 and P0155 on specific Chevy and GMC Pickups, Vans, and SUVs with either a 4.8L, 5.3L, or 6.0L V8.

To see if this test tutorial is the one you need for your specific GM vehicle, take a look at the 'Applies To:' box on the column on the right. If this tutorial doesn't cover your specific vehicle, take a look at the index of tutorials here: O2 Sensor Tutorial Index.

NOTE: In trying to keep this article as short as possible (and easy on the eyes), this tutorial jumps right into the testing of the front oxygen sensors on your GM pickup, SUV, or van.

This also means that I have left out a lot of basic stuff that you may need to know. The good news is that you can find this basic info here:

That tutorial (Testing P0135, P0141, P0155, P0161 O2 Heater Performance Problem) answers a lot of the most common questions like:

  • Symptoms Of A bad oxygen sensor heater element.
  • Where are the O2 sensors located?
  • What tools do I need?
  • What Does the heater Inside the oxygen sensor Do?

Circuit Descriptions Of The Upstream Oxygen Sensors

IMPORTANT: Your GM vehicle may use one of two different types of oxygen sensors depending on where it was built. This tutorial covers both. What's the difference? The difference is in the connector of the oxygen sensor. The images in the image viewer above will help in identifying them:

The oxygen sensors (Bank 1 Sensor 1 and Bank 2 Sensor 1) on your GM pickup, SUV, or van have 4 wires coming out of them.

2 wires are the ones that provide the PCM with a measurement of the oxygen content of the exhaust. The other two are the ones that turn on the heater element within the oxygen sensor.

The 2 wires that we need to be concerned about, to diagnose Trouble Codes: P0135 and P0155, are the Pink and Black wires of the O2 sensor connectors (both Bank 1 Sensor 1 and Bank 2 Sensor 2 have the Pink and Black wires).

Oxygen Sensor Bank 1 Sensor 1 Circuits
Pin Wire Color Description
A Tan HO2S Low Signal
B Purple HO2S High Signal
C Black Heater Element Ground
D Pink Heater Element 12 Volts (O2 sensor fuse)
Oxygen Sensor Bank 2 Sensor 1 Circuits
Pin Wire Color Description
A Tan w/ White stripe HO2S Low Signal
B Purple w/ White stripe HO2S High Signal
C Black Heater Element Ground
D Pink Heater Element 12 Volts (O2 sensor fuse)

Where To Buy The Oxygen Sensor And Save

You could buy the oxygen sensor at your local auto parts store but you'll end up paying quite a bit for it or you could buy it online and save a few bucks.

At the bottom you'll see two boxes with a photo of an oxygen sensor and a price. Why two different oxygen sensors? Because, depending where your specific GM pickup, van, or SUV was built, it'll have one or the other for the upstream oxygen sensors.

One oxygen sensor has a flat rectangular connector, the other type of oxygen sensor (GM used) has a square connector. You'll need to take a look at the connector to buy the right one.

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

In this section, I'll give you a brief run-down of what you'll need to test:

In a nutshell, your troubleshooting should start by making sure that the oxygen sensor heater element is getting power (10 to 12 Volts) and Ground.

  • Power is provided by the Pink wire.
  • Ground is provided by the Black wire.

If the O2 sensor is not getting power or Ground, then you've found the cause of the P0135 and/or P0155 diagnostic trouble code (DTC).

If you do find that the oxygen sensor's heater is getting both power and Ground, then the next step, is to measure the resistance of the heater element inside the oxygen (O2) sensor to see if it's fried or not.

As you can see, testing DTCs 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.

TEST 1: Checking For 12 Volts (Pink Wire)

The oxygen sensor's heater element only gets power when you turn the key to the ON position and/or when the engine is running.

IMPORTANT: Before I go any further, let me tell you that you should never test the O2 Senor's with the engine hot and/or running. Since the oxygen sensor's are bolted to the exhaust manifold or pipe, they get VERY HOT! This could result in severe burns!

With the key in the RUN position (but engine OFF), this voltage will range between 10 to 12 Volts DC on your multimeter.

OK, to get our P0135/P0155 DTC troubleshooting under way, this is what you need to do:

  1. Locate the upstream oxygen sensor you need to test
    • Bank 1 Sensor 1 is on the 'driver' side of the engine (P0135).
    • Bank 2 Sensor 1 is on the 'passenger' side of the engine (P0155).
  2. Jack up 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.
  4. Locate the Pink wire of the engine wiring harness oxygen sensor connector.
    • 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: 10 to 12 Volts are present in the Pink wire with the Key On Engine Off- This confirms that the oxygen (O2) sensor's heater element is getting juice.

The next step is to make sure that the oxygen sensor's heater element is getting a good Ground on the C circuit wire. For this test, go to: TEST 2: Checking Ground (Black Wire).

CASE 2: 10 to 12 Volts ARE NOT present in the D circuit wire with the Key On Engine Off- This usually means that the O2 sensor fuse, in the Engine Compartment Fuse Box is blown.

This also indicates that the other upstream oxygen sensor isn't getting power too. Check the oxygen sensor fuse and if blown, replace it and retest.

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