O2 Sensor Circuit Slow Response Bank 1 Sensor 2
Table of contents
- Possible Causes
- How To Fix
- Tech Notes
- Cost To Diagnose
- When is the code detected
- Possible Symptoms
- Description
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
How do I fix code P0139 MERCEDES-BENZ?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Tech Notes
- Mercedes Benz Code = 0511 (Right O2 sensor, after TWC): Aging (P0139)
- Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem.
Cost of diagnosing the P0139 MERCEDES-BENZ code
The cost of diagnosing the P0139 MERCEDES-BENZ code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
When is the code detected
The P0139 code is set when the Engine Control Module (ECM) detects that the rear O2 sensor takes more time to respond between rich and lean than the specified time.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- High Fuel Consumption
- Excessive Smoke from Exhaust
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.