TEST 2: Verifying The Heater Element Is Getting Ground

P0141 Trouble Code Diagnostic Tests (1990-1997 2.3L Ford)

So far you've verified that the downstream oxygen sensor on your Ford 2.3L Ranger (Mazda B2300) is getting battery voltage.

The next test is to check and confirm that female terminal number 1 of the downstream O2 sensor engine wiring harness connector is feeding ground to the heater element.

To verify this ground, you'll do a simple voltage test with your multimeter.

IMPORTANT: Be careful not to short this circuit to battery voltage (12 volts) or you run the risk of frying the PCM since the heater element's ground is provided internally by the PCM.

Alright, this is what you'll need to do:

  1. 1

    Locate the wire that connects to terminal number 1 of the O2 sensor's harness connector.

    The wire that connects to terminal number 1 is the White w/ Black stripe wire.

    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:

    1. Connect the red multimeter test lead to battery (+).
    2. Connect the black lead to terminal number 1 of the O2 sensor's harness connector.
  3. 3

    With the Key On, engine Off, your multimeter should register 10 to 12 Volts DC if the WHT/BLK wire is providing ground.

Let's take a look at your test results:

CASE 1: The multimeter registered 10 to 12 Volts DC- So far so good. Up this point, your tests have confirmed that your 2.3L Ford Ranger's (Mazda B2300) downstream O2 sensor is getting both power and ground.

The next step (and the last one) 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 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 wire that connects to terminal number 1 of the O2 sensor's harness connector and its ground point on the engine or chassis.

By an ‘open’, I mean that the wire is cut somewhere between it and its ground point. To confirm this, you can use a jumper wire to ground this circuit and repeat the test.

Repairing this ground issue will solve the P0141 issue you're having with your 2.3L equipped Ford Ranger (Mazda B2300) pickup.

TEST 3: Testing The Heater Element's Resistance

P0141 Trouble Code Diagnostic Tests (1990-1997 2.3L Ford)

The final step in your P0141 trouble code diagnostic is to check the downstream O2 sensor heater's internal resistance.

In this test, you'll be testing male terminals number 1 and number 2 of the downstream O2 sensor's connector itself and NOT the engine wiring harness connector.

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 number 1 and number 2 of the O2 sensor connector itself (which has male terminals).

  2. 2

    With your multimeter in Ohms mode... probe terminals number 1 and number 2 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: Your multimeter confirmed the indicated resistance- This test result tells you that your 2.3L Ford Ranger's downstream oxygen (O2) sensor's heater is OK.


CASE 2: Your multimeter showed an open circuit (OL)- This confirms that the downstream (Bank 1 Sensor 1) O2 sensor's heater element is fried.

Since you have:

  1. Checked that the downstream O2 sensor is getting power (TEST 1).
  2. Checked that the downstream O2 sensor is getting ground (TEST 2).

... you can now confidently replace the downstream O2 sensor knowing that this will solve the P0141 trouble code lighting up the check engine light (CEL).