If the oxygen sensor is going bad, the fuel-delivery and fuel-combustion systems will be thrown off. If a bad oxygen sensor disrupts the air to fuel ratio mixture, or too much fuel is injected into the engine, your vehicle’s gas mileage will be reduced.

To identify the source of any O2 sensor faults, consider the following steps:

• Read any fault codes using a diagnostic tool. Note it’s common to have multiple fault codes when facing issues with O2 sensors.
• Lambda sensors have an internal heater, so check the resistance of the heater – it will usually be quite low.
• Check the power supply to the heater – often these wires are the same color.
• Inspect the electrical connector for damage or dirt.
• Inspect the exhaust manifold and fuel injectors for leaks as well as the condition of the ignition components – these may affect sensor operation.
• Check the O2 sensor is reading correctly by confirming the O2 value with a four, or five gas emission analyzer.
• Use an oscilloscope to check the signal at both idle and approx. 2,500 rpm engine speed.
• Use live data to check for signal if the sensor wiring is difficult to access.
• Check the condition of the probe element protective tube for signs of damage and contamination.

The O2 Sensor (or Lambda Sensor) is typically mounted in the exhaust system just upstream from the Diesel Oxidation Catalyst (DOC).

If your check engine light is turned on, here are the codes associated with a DPF Differential Pressure Sensor. Any part or component should not be replaced only with reference to a Diagnostic Trouble Code (DTC). The vehicle service manual should always be consulted for more information on possible causes of the fault, along with required testing.