Disconnect differential pressure regulator connector from side of regulator. Using Adapter (1315 A/1 ), connect Multimeter (US 1119 ) to differential pressure regulator and to the connector removed from regulator.
Set multimeter to 200 mA DC scale. Disconnect O2 sensor connector. Start engine and let idle. Note reading on multimeter. Ground male end of O2 sensor connector.
Observe multimeter. Current should increase from 9 mA to 11 mA after 15 seconds. If multimeter reading is not as specified, check wiring between FICU and O2 sensor harness connector.
If no break in wiring is found, replace FICU. Reconnect O2 sensor (Green) wire. Start engine. Raise engine speed to approximately 3000 RPM for a few seconds.
Differential pressure regulator current must return to original mA value and fluctuate approximately 1-3 mA in -10 mA to +10 mA range. If current does not return to original mA value or does not fluctuate, replace O2 sensor.
To check O2 sensor heating element, disconnect O2 sensor heating element connector from harness connector. Connect multimeter between connector terminal No. 1 and No. 2. See Figure .
Turn ignition on. Multimeter should read 12 volts. If multimeter does not read as specified, repair break in wiring. Connect multimeter between terminals No. 1 and No. 2 of O2 sensor heating element connector. See Fig 1 .
Multimeter should read 3-15 ohms. If multimeter does not read as specified, replace O2 sensor.

Fig 1: View of O2 Sensor Heating Element Connector

Courtesy of AUDI OF AMERICA, INC.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Oxygen Sensor