DTC P0155 – How To Test a LQ4 Oxygen Sensor

DTC P0155 – How To Test a LQ4 Oxygen Sensor


The DTC of P0155 informs the driver that there’s a problem with the upstream 02 sensor in the 6.0 liter LQ4 Chevy engine. More specifically the error code is telling you that the primary 02 sensor on the Bank 2 side is having the problem. Today we’ll be showing you how to resolve this issue in a BAR legal swapped LQ4 Nissan 240SX, although this applies to any LQ 6.0 liter engine in the 1999-2006 first generation Chevy Silverado.

OBDII trouble code P0155 can be fixed by simply replacing the Bank 2 upstream oxygen sensor in your 6.0 liter LQ4. But before you go out and purchase one, it’s a good idea to learn how to test a LQ4 oxygen sensor.

Have you seen our Budget LS1 Swap Guide?


Where is my Bank 2 oxygen sensor?


The Bank 1 and Bank 2 designations can be difficult to understand and locate, especially if you aren’t familiar with the engine. Because your LQ4 has 4 total oxygen sensors, you need to know which one you’ll be testing. In our 6.0 liter LQ4 powerplant, Bank 2 is located on the side of the engine that has cylinder 2, 4, 6 as well a 8, otherwise known as the passenger side.

This oxygen sensor is located in the exhaust manifold, and before the Y pipe that leads with your catalytic converters. Because the P0155 is for Bank 2 Sensor 1, this is the upstream or primary 02 sensor.


Your primary LQ4 oxygen sensor carries a part number of 25333817 or 12572705, and is connected using a trapezoid shaped oxygen sensor connector. If your LQ4 is before 2003, your oxygen sensor will be square shaped and slightly differ.


Using the image above, you’ll be using a multimeter to test the operation and functionality of your Chevy oxygen sensor. If you are not sure on how to use a multimeter, check out our handy guide here.

Possible causes of OBDII DTC P0155


The specific verbiage of this trouble code makes it easy to diagnose, because we already know which sensor it is. Replacing the trouble oxygen sensor and clearing the check engine light code of P0155 will take care of the issue. Our how to test a LQ4 oxygen sensor DIY guide is here to show you how to test before replacing your oxygen sensor in your Silverado.

How to test your LQ4 oxygen sensor for power


Remember that the LQ4 we are working out of is found in a legally swapped Nissan 240SX, and this 6.0 liter was transplated from a 2003 Chevy Silverado. For the purposes of this how to test a LQ4 oxygen sensor article, you can use this schematic to test any LQ4 oxygen sensor from 2003-2005.

To test your LQ4 oxygen sensor for power, you will need to connect the black lead of your multimeter to the negative post on your battery.

  1. Locate your primary upstream Bank 2 oxygen sensor ( passenger side )
  2. Unplug your LQ4 oxygen sensor
  3. Probe PIN D on the wiring harness side of the connector for power

You should have voltage at PIN D, which is a PINK wire that terminates at circuit number 539 on your LQ4 or LS1 ECU. If you have power at this wire, move ahead to checking for the low reference ground signal, this wire is PIN E, which is a black wire with white stripe. This wire terminates at circuit number 3113 which grounds several sensors at once.

So you now know that your upstream Bank 2 oxygen sensor is receiving power and ground, now it’s time to test the heater element. This is done by measuring the resistance across two posts, in this case it would be PIN A and PIN B.

How to test your LQ4 oxygen sensor heater element


Now it’s time to measure the resistance in your heater element, put your multimeter into Ohms Ω mode and let’s get to work. This time because you’ll be testing the oxygen sensor directly, remember that you are measuring the SENSOR side of the harness connector.

Put one probe of your multimeter to PIN A which is a tan wire. This wire represents the H02S Low signal, and the second wire you’ll be probing is PIN B which is a purple wire with white stripe.


There should be a reading between 5-19 Ω letting you know that your oxygen sensor is A-OK.  If your oxygen sensor resistance reading falls outside of these numbers or it shows an open circuit, it’s time to replace your oxygen sensor to fix your P0155 trouble code.

You now know how to test a LQ4 oxygen sensor to eliminate the OBDII DTC of P0155, if you have any questions or comments regarding our DIY How To, leave them for us below.


  1. I got a ls motor from an unknown source and I’m not sure what you make or what engine it is. I thought maybe a Sierra. how can I tell

    • Hi Sean, thanks for reading

      Nice swap you’ve got there but if you are working with a 6.0 liter GEN III GM engine, you are going to want to properly replace your oxygen sensor. You cannot truly solder anything onto the 02 wiring without the right solder, but if you want to crimp connections and match it up to the wiring harness in your Miata, the pinouts on are this page.

      Thanks for commenting, let us know how it turns out