Engine Light ON (or Service Engine Soon Warning Light),High Fuel Consumption,Excessive Smoke from Exhaust
P0139 MERCEDES-BENZ Possible Causes
Faulty Rear Heated Oxygen Sensor Bank 1,Rear Heated Oxygen Sensor Bank 1 harness is open or shorted,Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
P0139 MERCEDES-BENZ Description
This fault code is stored in the Engine Control Module (ECM) when the output from the exhaust gas oxygen sensor is not as expected. The engine control module analyses the signal generated from the exhaust gas oxygen sensor to monitor how quickly the sensor can switch from one condition to another. An example of this is a voltage shift from a low voltage to a high voltage during full load enrichment. Another example is a voltage shift from a high voltage to a low voltage during over-run fuel shutoff. With a narrow-band oxygen sensor a low voltage indicates a lean mixture and a high voltage indicates a rich mixture. Narrow-band oxygen sensors can only act as a rich or lean indicator. They cannot measure the actual air/fuel ratio. A wide-band oxygen sensor is required to measure actual air/fuel ratio. A normal allowable time to shift from lean to rich is approximately 100 milliseconds. A normal allowable time to shift from rich to lean is approximately 150 milliseconds. The response of the oxygen sensor should be measured using an oscilloscope rather than scantool live data. This is due to the scantool receiving data from the engine control module which has already been processed so the data may seem slower when displayed on the scantool.
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