Diagnosing a BAD oxygen sensor that's making the check engine light light (CEL) up with a P0141 isn't hard at all.
In this tutorial, I'll show you how to do it with a multimeter. This article applies to several GM makes and models... you can check out the ‘Applies To:’ chart on the right column to see if your vehicle is included.
In case you're wondering, where the oxygen (O2) sensor that the code P0141 is accusing of being BAD is, this bad boy is located on the exhaust pipe after the catalytic converter.
Contents of this tutorial:
- Symptoms Of A BAD Oxygen Sensor Heater Element.
- What Tools Do I Need to Test Code P0141?
- What Does The Heater Inside The Oxygen Sensor Do?
- Circuit Descriptions Of The Downstream Oxygen Sensor.
- TEST 1: Checking 12 Volts to O2 Heater.
- TEST 2: Checking The O2 Heater's Ground Circuit.
- TEST 3: Checking The O2 Heater Element's Resistance.
You can find this tutorial in Spanish here: Cómo Probar El Código P0141 Con Multímetro (3.5L GM) (at: autotecnico-online.com).
Symptoms Of A BAD Oxygen Sensor Heater Element
If the heater element within the oxygen (O2) sensor goes bad, the PCM (Powertrain Control Module = Fuel Injection Computer) will light up the check engine light (CEL) on your instrument cluster.
You'll also see one or several of the following symptoms of a BAD oxygen sensor heater:
- Diagnostic Trouble Codes:
- P0141: HO2S Heater Performance Bank 1 Sensor 2.
- BAD gas mileage.
- Won't pass the emissions test.
What Tools Do I Need to Test Code P0141?
Here's a basic list of tools you'll need:
- A multimeter.
- 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).
- Scan tool.
- Don't have one?... check out my recommendation: Abe's Scan Tool Recommendation.
- 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?
The oxygen (O2) sensor has to reach a certain temperature to activate and start measuring the oxygen content of the exhaust.
As surprising as it may seem, 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 it so that it stays hot as long as the PCM commands it.
The only thing that sucks about this... is that the heater element (inside the oxygen sensor) doesn't last forever and fails very frequently.
Circuit Descriptions Of The Downstream Oxygen Sensor
If you take a close look at the connectors (engine wiring harness connector and the O2 sensor connector), you'll see that four letters are embossed on both of them.
These four letters are A, B, C, and the letter D. These are the letters that you'll need to test the rear oxygen sensor with the instructions in this tutorial.
IMPORTANT: One last thing... the wires have colors only on the engine wiring harness side AND THESE COLORS MAY NOT MATCH THE ONES ON YOUR VEHICLE (On the oxygen sensor side... there's really no dependable way to identify the circuits with their colors). But this is no cause for concern, since you can still identify them with the letters embossed on the O2 sensor connector.
Just to further clarify this, if the colors in the chart below don't match those for the rear (post-catalytic converter) oxygen sensor.... you can still use the info in this article! Since the circuit descriptions are the same, all that you have to do is identify the wire by its letter.
|Heated Oxygen Sensor Circuits|
|A||Tan w/ White stripe||HO2S Low Signal|
|B||Purple w/ White stripe||HO2S High Signal|
|C||Black w/ White stripe||Heater Element Control Circuit (Ground)|
|D||Pink||Heater Element Battery Voltage|