There’s more than just one Silverado O2 sensor in your Chevy truck, especially when it’s an OBDII Silverado or built after 1996. Today I’ll be showing you how to test the primary or upstream O2 sensor in a 2004 Chevy Silverado with a 5.3 liter Vortec engine in it. The upstream Silverado O2 sensor is also known as the primary or front oxygen sensor. Because there’s two of these upstream sensors, I’ll be showing you how to test both in your GEN III Chevy truck.
When the upstream Chevy Silverado oxygen sensor goes out in your truck, you’ll see a warning light turn on. This is also known as your Chevy Silverado check engine light. This code tells you that your engine computer is receiving a signal from the front O2 sensor that’s out of range, or no signal at all.
When there’s a problem from your Silverado O2 sensor signal, your truck computer won’t know how to manage the fuel delivery to you Vortec engine. In order to retrieve the OBDII code that’s flagged in your truck, you’ll need to use a scan tool. Just some of the trouble codes you may see can include P0135, P0141, P0155 or P0161.
If you’ve pulled out your OBDII trouble codes and see that any of these codes popped up, it’s a sign that your upstream Silverado O2 sensor has a serious problem. In order to complete this DIY wiring tutorial you are going to need a digital multimeter.
If you happen to own the older generation Silverado, check this guide here for how to test the Silverado oxygen sensor. This particular guide is for the 2003-2006 Chevy Silverado using the 5.3 liter engine and square primary oxygen sensor plugs.
Before you begin locate the primary Silverado O2 sensor that’s screwed into your exhaust manifolds. Once you’ve located them, turn your Silverado ignition to the “ON” position. This sends a power and ground signal from your PCM to the upstream oxygen sensors.
As I mentioned earlier, there’s two sets of upstream oxygen sensors. These are known as BANK 1 and BANK 2. What’s the difference between Bank 1 and Bank 2 oxygen sensors? Bank 1 is the side that cylinder 1 is located on. Look at the spark plug wires from your Silverado ignition coils to see which cylinder is #1.
Testing the Silverado O2 sensor heater circuits
The first wire you’ll be checking is the power wire, otherwise known as the Silverado O2 sensor heater circuits. Once you have the upstream Silverado O2 sensor unplugged, you’ll use the Silverado oxygen sensor wiring diagram below to test the circuit.
Remember you are testing the HARNESS side of your Silverado O2 sensor. The pin you are checking for is PIN D on the harness.
With the key inserted and ignition turned to the “ON” position you should have 12 volts of power here. The Bank 1 Sensor 1 Silverado O2 heater wire is a PINK wire. Bank 2 shares a similar color and location for the heater wire, PINK and PIN D.
If you have power at the heater wires, the next part to check is the ground. Like the heater element the ground signal is sent by your Silverado PCM. Because of this you need to make sure you are not touching the ground to PIN D otherwise you run the risk of burning out your engine computer.
The Bank 1 upstream O2 sensor has a Light Blue wire for the heater element ground. Depending on the year of your 5.3 liter Silverado this wire might also be BLACK with a WHITE wire. The pin to check is PIN C on the Harness side of the Silverado O2 sensor.
If it’s Bank 2 you are checking, you will need to check the same location of PIN C. The Bank 2 Silverado O2 sensor heate ground has a PURPLE wire with a WHITE stripe in it. It could also be a LIGHT GREEN wire as well but the position of PIN C is the same.
Do you have power and ground but your upstream oxygen sensor is still giving you problems? The last leg of the test is to use your multimeter to test the internal resistance. This is a test to see if the Silverado O2 sensor has failed on you. We were testing at the HARNESS side for the last test, this test involves testing at the SENSOR side.
Gently probe PIN C and PIN D of the SENSOR side of the Silverado oxygen sensor. Remember you are resting the SENSOR side of the equation, and that you need to turn your multimeter dial to measure resistance Ω.
By measuring the internal resistance of your upstream Silverado oxygen sensor, it should return a value between 5 to 16 Ω (Ohms).
If the measurements fall outside of this range, your Silverado O2 sensor has died. Remove it and install a replacement upstream oxygen sensor to fix your Silverado. After you’ve installed the new upstream sensor, use your OBDII scan tool to clear your Silverado check engine light.
The other wires in your Silverado upstream O2 harness are PIN A for HO2S Low Signal, and PIN B for HO2S High Signal. For all Bank 1 oxygen sensors, PIN A is usually a TAN colored wire, and PIN B is a PURPLE wire with a WHITE stripe. For Bank 2 upstream O2 sensors, PIN A is a TAN wire while PIN B is a PURPLE wire.
Have any questions regarding our Silverado O2 sensor testing guide? Leave us a comment below and let us know!