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 an 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:

• 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.
• 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: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).
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: ZM301 OBD2 Scanner Diagnostic Tool (Amazon affiliate link).
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).

Oxygen Sensor Test Summary

Testing the oxygen sensor is not that hard to do, In my opinion, the hardest part is just getting to it to test it.

So, I'm gonna' offer you some very important safety precautions:

1. Test the oxygen sensor(s) with a cold engine.
   • Whether the oxygen sensors is before or after the catalytic converter, they get HOT if the engine has been running!
   • This extremely hot temperature will cause serious burns on your hands and/or fingers.
   • If you've had your car running, let the engine cool down completely before starting your tests.
2. Use Jack Stands.
   • To get to the O2 sensor after the catalytic converter, you'll have to raise your vehicle.
   • Always use jack stands while working under your vehicle!
   • A jack should never ever be trusted to hold up the vehicle for a long period to time.
3. Use Safety Glasses.
   • Protect your eyes from all of the mud, dirt, etc that will caked up underneath your vehicle (and which you'll disturb when testing the rear (downstream) O2 sensor.

OK, having gotten these safety/precaution suggestions out of the way, in this section, I'll briefly describe what the oxygen sensor heater element test (for P0135 and P0141) consists of and then where to find the in-depth, step-by-step, testing tutorials you need.

OK, testing the oxygen sensor's heater element consists of 3 basic tests things. These are:

1. Make sure that the O2 sensor's heater element is getting battery power (10 to 12 Volts DC) with the Key On Engine Off.
2. Make sure that the O2 sensor has a Ground for those 10 to 12 Volts.
3. And last, check the resistance of the O2 sensor's heater element to see if it's fried and registering an 'open'.

All in all, testing the oxygen sensor heater element (inside the O2 sensor itself) is a pretty easy test.

What complicates things a little, is just knowing which wires are the ones that supply this battery power and Ground since each oxygen sensor has 4 wires coming out of it.

To further help you in effectively diagnosing each O2 sensor (and trouble codes: P0135, P0141), here's a list of articles that will help you to diagnose these codes in a step-by-step manner:

• Testing Trouble Code: P0135 (GM 3.8L 1994-1996).
• Testing Trouble Code: P0135 (GM 3.8L 1997-2003).