Oxygen Sensor Heater Test -P0141 (2.2L Chevy S10 - GMC Sonoma)

TEST 2: Verifying The Heater Element Is Getting Ground

The next step is to check that the black (BLK) wire of the rear O2 engine wiring harness connector, is feeding the heater element with Ground.

Just like we did to confirm power to the O2 sensor's heater element, we'll do a simple multimeter voltage test (to see if Ground is indeed present or not).

IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the BLK wire of the engine wiring harness sensor connector.

These are the test steps:

1. 1

   Locate the BLK wire of the O2 sensor's engine wiring harness connector.
   
   NOTE: Remember, you'll test the wire that's on the engine wiring harness connector side and NOT on the O2 sensor itself.

2. 2

   Place your multimeter in Volts DC mode and connect the red multimeter test lead to battery (+).
   
   With the black multimeter test lead, probe the BLK wire of the O2 sensor's harness connector.

3. 3

   With the Key On, engine Off, this wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: The multimeter confirms that the BLK wire is feeding Ground since it registered 10 to 12 Volts DC. This confirms the rear O2 sensor's heater is being fed with Ground.

So far you've confirmed that the downstream O2 sensor's heater element is getting both power and Ground. The next step is to check the heater element's resistance with your multimeter. For this test, go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: The multimeter confirms that the BLK wire IS NOT feeding Ground since it DID NOT register 10 to 12 Volts DC. Re-check all of your connections and make sure you're testing the correct terminal.

If your multimeter still doesn't register the 10 to 12 Volts DC, then the most likely cause of this missing Ground is an 'open' in the BLK wire between the O2 sensor's harness connector and chassis Ground.

TEST 3: Testing The Heater Element's Resistance

After checking the basics, your diagnostic tests have so far confirmed:

• A P0141 trouble code is lighting up the check engine light on your S10 or Sonoma.
• The rear O2 sensor is getting power on the PNK wire (TEST 1).
• The rear O2 sensor is getting Ground on the BLK wire (TEST 2).

In this last test section, we're gonna' verify that the rear O2 sensor's heater resistance is within factory specification.

If the resistance is not within specification, then we now know the O2 sensor is bad and the cause of the P0141: HO2S Heater Circuit Sensor 2 trouble code.

NOTE: Just a reminder that the downstream oxygen sensor has to be completely cold before proceeding with this test since the manual calls for the O2 sensor to be at room temperature for the resistance test.

OK, this is what you need to do:

1. 1

   Locate the O2 sensor terminals C and D of the O2 sensor connector itself (not the engine wiring harness O2 connector).

2. 2

   With your multimeter in Ohms mode, probe terminals C and D of the O2 sensor itself.

3. 3

   If all is OK, you should see about 3 to 30 Ωs on your multimeter.
   
   If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL) or a number over 10 K Ωs.

Let's take a look at your test results:

CASE 1: The rear O2 sensor's heater resistance is within spec.. This test result tells you that rear oxygen sensor's heater is OK.

CASE 2: Your multimeter showed an open circuit (OL). This tells you that the downstream O2 sensor's heater element is fried. Replacing the downstream O2 sensor with a new one will solve the P0141 trouble code lighting up the check engine light (CEL).

Here are some more specifics: Since you have:

• Confirmed that the PNK wire is feeding power to the rear O2 sensor's heater element (TEST 1).
•      -AND-
• Confirmed that the BLK wire is feeding Ground to the rear O2 sensor's heater element (TEST 2).
•      -AND-
• In this test, you have confirmed that the heater element's resistance is out of specification.

Therefore, all of your test results indicate that you can correctly conclude that the downstream O2 sensor needs to be replaced with a new one.

More 2.2L GM Diagnostic Tutorials

You can find a complete list of 2.2L GM tutorials in the following 2 indexes:

• GM 2.2L Index Of Articles.
• GM 2.2L Index Of Articles (at troubleshootmyvehicle.com).

Here's a small sample of the tutorials you'll find in the indexes:

• How To Test The Front Oxygen Sensor With A Multimeter (2.2L GM).
• How To Test The GM 2.2L Throttle Position Sensor (TPS).
• How To Test The GM 2.2L Ignition Coil Pack.
• How To Test The Fuel Injectors With a Multimeter (GM 2.2L) (at: troubleshootmyvehicle.com).