P0135, P0141 Test Basics O2 Heater Performance Problem (GM 3.8L)

In this tutorial, we'll cover some of the basics you need to know to troubleshoot and diagnose diagnostic trouble codes P0135 and P0141 on your 3.8L equipped GM vehicle.

If you've researched these two trouble codes (online or in a automotive repair book), you know by now that each indicates a problem with the oxygen (O2) sensor's internal heater element.

And if you've been wondering if you can test the O2 sensor to see if its heater element is fried or not, well you've come to the right place to find out.

Let's get started.

Symptoms Of A Bad Oxygen Sensor Heater Element

The most obvious symptom, you'll see when the O2 sensor's heater element goes bad, is the check engine light (CEL) shining nice and bright on your instrument cluster.

You'll also see one or several of the following symptoms of a bad oxygen sensor heater:

1. Diagnostic trouble codes:
   • P0135: HO2S Heater Performance Bank 1 Sensor 1.
   • P0141: HO2S Heater Performance Bank 1 Sensor 2.
2. Bad gas mileage.
3. Won't pass the emissions test.

How To Locate The Oxygen Sensors

Your 3.8L Buick (Chevy, Pontiac, or Olds) has a total of two heated oxygen sensors (also known as O2 sensors).

I'm sure, that by now, you've come across terms that refer to these two sensors as being either an upstream oxygen sensor or a downstream oxygen sensor.

You've also read that some are located before or after the catalytic converter. You've also noticed that the trouble code descriptions identify the O2 sensors as being on Bank 1 or Bank 2 and then identified as Sensor 1 or Sensor 2.

All this may leave you scratching your head and wondering where exactly these oxygen sensor are. Well, we'll take a closer look at all of this in the next two headings:

1. Bank 1 Sensor 1
   • This oxygen sensor is located BEFORE the catalytic converter.
   • This O2 sensor is also called the upstream oxygen sensor.
   • When its heater element goes bad, you'll see a diagnostic trouble code P0135.
2. Bank 1 Sensor 2
   • This oxygen sensor is located AFTER the catalytic converter.
   • Also known as the downstream oxygen sensor.
   • When its heater element goes bad, you'll see a diagnostic trouble code P0141.

The least you need to know: In automotive lingo, Bank 1 refers to the bank (side) of the 3.8L engine that has cylinders 1, 3 and 5.

In describing the oxygen sensor as Bank 1 Sensor 1 and Bank 1 Sensor 2, you might be wondering where are Bank 2 Sensor 1 and Bank 2 Sensor 2? Well, since your vehicle only has two oxygen sensors and not four, referring to these two as being on Bank 1 is the simplest way to identify them within the limits of the Bank 1 and Bank 2 naming convention.

What Tools Do I Need To Test Codes P0135, P0141?

Here's a basic list of tools you'll need:

1. A multimeter.
   • You'll only be using the multimeter to check voltage DC and resistance (Ohms).
   • If you need to upgrade or buy a multimeter, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
2. Scan tool.
   • To actually test the oxygen sensor's heater element, you don't need a scan tool but it does come in super handy to read the diagnostic trouble code(s).
   • Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.
3. Wire piercing probe.
   • Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
   • If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.

What Does The Heater Inside The Oxygen Sensor Do?

Each one of the two oxygen (O2) sensors on your 3.8L Buick (Chevy, Olds, or Pontiac) has to reach a certain temperature to activate and start measuring the oxygen content of the exhaust.

This may come as a bit of a surprise, but as hot as the exhaust is, it's still not hot enough to maintain the O2 sensors at the ideal temperature they need to operate 100% of the time. That's right, the temperature of the exhaust gas isn't enough to keep the oxygen sensor hot enough to perform 100% of the time.

The solution? Place a heater element inside of the upstream and downstream oxygen sensors, so that that they stay hot as long as the engine in your vehicle is running.

This is the reason why the oxygen sensors have 4 wires. Two of them are for the heater element inside the oxygen sensor and the other 2 are for the oxygen sensor signal itself.

If you're here reading this, then you now know that the heater element (inside the oxygen sensor) doesn't last forever (they fail very frequently).