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!
I have a 2001 harness and im having issues with my o2 reading on hp tuners..both are flatline bank one has a grey plug and bank 2 a black plug…i may have two downstream instead of upstream..
Hi John, thanks for reading this Silverado oxygen sensor guide.
What does your HP tuners unit say for the bank 1 Silverado 02 sensor versus the bank 1 oxygen sensor? If these values are low and won’t respond to throttle, chances are you may have bad 02 sensors.
Let us know how your Silverado 02 sensors turn out! Thanks!
Very helpful, thank you.
Can you explain how to check the ground wire on the harness side? Set to ohms and place one probe on PIN C and the other on the engine block? Or does one probe go on the PIN C and the other on PIN D? Does it matter which probe goes where? What should the reading be?
Thank you very much.
Hi Richard, thanks for commenting.
The Silverado ground wire check is very easy to perform. All you need is a multimeter. Place the red lead on your positive terminal of your battery, and the black lead on your ground wire. If you’ve got 12v, you are golden.
Thanks for reading. Let me know how your Silverado 02 sensor issues turn out!
I get a reading of 16.7 ohms that is over the range of 5 through 16. But I am still good right or no?
How do you test the 12v power wire without touching a ground somewhere either on the engine, frame or else where. Can you tell me where to put the leads for the multimeter for the power wire? I have a 2003 GMC Sierra, which is basically the same as the Chevy Silverado.
You did not answer my question. In the article you state when testing the 12v wire, do not touch the ground wire or you may stand the chance of ruining your computer. I understand the use of a multimeter, so you would touch the 12 v wire with the positive lead, so where would you touch the ground to get the reading for the 12v wire? Do you touch the negative to the negative post of the battery, or ground it to the frame? Please answer the question as I do not want to burn out my computer.
Hi Douglas, when using a multimeter use the ground from your battery for best results.
Thanks for commenting!
I have done a LS 3 motor swap from a 2000 gmc sierra 5.3. I have issues with both front oxygen sensors. I tested as you suggested and I have no ground at either sensor. Where do I go from here?
Computer problem? I have power on both and have swapped sensors multiple times. The current ones have about 16 ohms resistance.
Hey Mike, sounds like an awesome project.
So no grounds at the 02 sensors in your LS swap? You have a break in the ground aggregator ( pack of grounds in engine loom ) or a bad ground from the ECU. I would start there.
Hope that helps
Hello,hope you can help me i have power on both pink wire of the o2 sensor for the heater circuit harness side and have 12v ground from the computer. But when i put my meter lead on the signal wires on the harness side i get 11 v and 9v when in testing power koeo to o2 sensor , checking ground i only get 12v on the black wires harness side the other three wire are good no voltage . Is this correct ?? Or the pcm is bad ??? Thanks for your help
My 02 sensor read correct 5.5 ohms
Hi Omar, no if you have a traditional 4 wire 02 sensor, you will be looking for 2 hot or heater wires. Then there’s a ground and signal. Hope that helps!
what do you mean by sensor side and harness side?what are the color code on
4 pin 02 sensor for 1996 chevy truck 5.7
Hi Tony, so when I say the harness side, you are looking at the 02 sensor FROM the harness. When I say the sensor side this is the orientation when you look from the sensor, at the car or towards the harness.
does that make sense? Hope so! Thanks for reading!
Thanks for the information. 6.0 Bank two and sensor one: On the harness side, the pink wire is 12+ volts with a battery ground but when I rely on the ECU to provide the ground (probe on terminal C and D), the voltage drops in half (a bit over 6 volts). Is that correct? Once ECU relies on heated O2 data, the voltage for b2s1 drops to almost zero and short term fuel trim goes crazy.
Yes that is correct. when the sensor is cold that’s the reading you should be seeing.
Hope that helps! Thanks for reading!
VERY USEFUL INFORMATION THANK YOU BUT I HAVE MY OWN ISSUES I AM RUNNING LONG TUBE HEADERS AND WENT TO MY TUNER TO GET IT TUNED HE TOLD ME MY O2 SENSORS ARE OUT SO I CHANGED THEM BRAND NEW AND THEY STILL WEREN’T READING HE SHOWED ME THEY WERE STUCK AT 450 V HE TOLD ME WHEN YOU STEP ON THE GAS IT SHOULD SHOOT UP TO 1000 SO I CHECKED MY VOLTAGE IM GETTING THE 12 VOLTS TO MY HARNESS AND I CHECKED MY LOW AND HIGH ON THE HARNESS I GOT 0.4 WHICH IS IN SPEC AND MY SENSORS ARE NEW NOW I KNOW THEY COULD BE FAULTY BUT BOTH AT THE SAME TIME I DO NOT KNOW WHAT TO DO NEXT IM STUCK HERE ANY HELP I WOULD APPRECIATE
Hi there Griffin,
Those values don’t seem to make much sense, especially as your 02 sensor is more than likely 0-1 volt or 0-3 at best. What datalogger are you using?