TEST 2: Verifying The Heater Element Is Getting Ground
If you have already confirmed (in TEST 2) that the front right oxygen sensor (HO2S 2/1) is getting battery power, then your next step is to confirm that it's getting Ground.
Just like we did when we checked for battery power, we'll check for Ground by doing a simple multimeter voltage test.
NOTE: 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/RED wire of the engine wiring harness sensor connector.
IMPORTANT: Your Grand Vitara's PCM is the one that provides Ground (internally) for the heater. Be careful and don't accidentally or intentionally short the BLK/RED wire to battery voltage or you'll fry the PCM. The multimeter voltage test described below is a safe way of testing this Ground.
These are the test steps:
Locate the BLK/RED 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.
Place your multimeter in Volts DC mode and connect the red multimeter test lead to battery (+).
Probe the BLK/RED wire of the O2 sensor's harness connector with the black multimeter test lead.
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 BLK/RED wire is feeding ground since the multimeter registered 10 to 12 Volts DC. This confirms the right front 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 BLK/RED wire IS NOT feeding ground since 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 BLK/RED wire between the O2 sensor's harness connector and the PCM (the PCM supplies this Ground internally).
TEST 3: Testing The Heater Element's Resistance
So far, your P0155 troubleshooting tests have confirmed that:
- A P0155 trouble code is stored in your Grand Vitara's PCM's memory.
- The BLU wire is feeding the right front O2 sensor (HO2S 11) with power (TEST 1).
- The BLK/RED wire is feeding the right front O2 sensor with Ground (TEST 2).
The last thing we need to do, before condemning the O2 sensor as bad, is to verify that its 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 P0155: Heated Oxygen Sensor Circuit Malfunction Bank 2 Sensor 1 trouble code.
NOTE: Just a reminder that the exhaust system and oxygen sensor have to be completely cold before proceeding with this test. Also, the manual calls for the O2 sensor to be at room temperature for the resistance test.
OK, this is what you need to do:
Locate the O2 sensor terminals 3 and 4 of the O2 sensor connector itself (not the engine wiring harness O2 connector).
With your multimeter in Ohms mode, probe terminals 3 and 4 of the O2 sensor itself.
If all is OK, you should see about 5 to 7 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 multimeter confirms the resistance is within 5 to 7 Ohms- This test result tells you that the right front oxygen sensor's heater is OK.
CASE 2: Your multimeter showed an open circuit (OL). This confirms that the O2 sensor's heater element is fried. Replacing the O2 sensor with a new one will solve the P0155 trouble code lighting up the check engine light (CEL).
Here's a more detaied explanation of why the O2 sensor is bad:
- TEST 1 confirmed that the O2 sensor's heater is getting power (TEST 1).
- TEST 2 confirmed that the O2 sensor's heater element is getting Ground (TEST 2).
- In this test you have confirmed that the heater element's resistance is out of specification.
Taking all of the above into account you can correctly conclude that the O2 sensor needs to be replaced with a new one.