TEST 3: Checking The O2 Heater's Resistance
So far, you've checked and confirmed that the the right front oxygen sensor is getting both power and Ground (TEST 1 and TEST 2).
The next step, and the last one, is to check the internal resistance of the right front oxygen sensor's heater element.
This is a pretty simple test that you'll do with the multimeter in Ohms mode.
NOTE: The illustration above shows the connector of the oxygen sensor itself. The resistance test is done on the O2 sensor's connector and NOT on the O2 sensor engine wiring harness connector.
Alright, these are the test steps:
Locate the two male terminals of the O2 sensor's connector shown in the illustration above.
NOTE: To correctly identify the two terminals, keep in mind the top locking tab on the connector. The orange arrow in the illustration above also refers to this top locking tab.
Place your multimeter in Ohms mode and measure the resistance between the two pins.
Remember, the O2 sensor connector itself has male terminals. The O2 sensor engine wiring harness connector has female terminals.
If all is OK, your multimeter should register 3 to 30 Ohms.
If the heater element is fried, your multimeter will show an open, usually indicated by the letters OL or a resistance in the thousands (K Ohms).
Let's take a look at what your test results mean:
CASE 1: The O2 sensor's heater element is within specification (3 to 30 Ohms). This test result tells you that the O2 sensor's heater is OK.
CASE 2: The O2 sensor's heater element IS NOT within specification. Double check your multimeter connections and repeat the test. If the resistance is still not within the Ford factory manual specification of 3 to 30 Ohms, then the O2 sensor is bad and needs to be replaced with a new one.
Oxygen Sensor Locations
NOTE: The above illustration is for dual exhaust Ford V8 and V6 equipped vehicles. The Ford vehicles covered by this tutorial are dual exhaust equipped with a total of 4 oxygen sensors.
The illustration below is for single exhaust Ford V8 and V6 equipped vehicles, I included the illustration below for comparison purposes and to aid you in further locating the right front oxygen sensor (HO2S-11).