Troubleshooting for Wideband AFR sensor (28-BOSCH)

There is 2 quick tests to verify if the sensor is operational.

1- Continuity test

* This test is done on the sensor only.
Use a multimeter to test the Ω of the sensor’s connector at ambient room temperature.


Sensor’s Connector

Connector Positions

Sensor’s Connector Positions

Continuity Test

If reading appear on the multimeter, this indicates that the continuity is good, therefore the sensor is OK. At room temperature, the reading is between 2.5 and 5Ω.
If OL (open lead) shows on the multimeter chances are that the sensor would be defective.

* If test 1 fails, do not attempt test 2.

2- Operational test with butane

* This test is done with meter connected to 12V DC power and sensor connected to the meter.
When you turn on the meter, the first thing to display in the screen is the version of the software.
R8 will indicate that this is the latest updated version.  If display shows R7, R6 or less, this means that the meter is over 5 years old.

Wideband Air/Fuel Ratio Meter

BA004068 Wide band AFR meter

The meter will then go through its starting set-up by going up to 100 and ready to operate. You may start the test.
Use a butane torch and get the sensor very close to the tip of the torch (you can use a mechanic glove as a kind of seal). Be careful, the sensor becomes hot. Turn on the torch BUT DO NOT LIT THE FLAME. Sending butane to sensor should show reading on the meter (reading vary depending of the quantity of butane sent).

Butane Test

Butane Test

If you have reading on the meter by doing this butane test, it indicates that the sensor is working fine. If not, chances are that the sensor appears to be defective.