My car indicates check engine sigh with following two codes 1: p0139 2: p0140

You still have a problem with all the O2 sensors Bbank 1 Sensor 1, Bank 2 Sensor 1 and Bank 2 Sensor 2) - if they are all the correct ones and are correctly installed and connected, then you need to carefully check the wiring harness and wire connections from them to the ECU. the P0300 just means random engine misfires.

Before replacing a part diagnostic's for code P0140 need to be done . May not be a part , could be wiring , PCM etc....
https://www.obd-codes.com/p0140

02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

Read more at: http://www.obd-codes.com/p0140
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P0140 - 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
The causes for a P0140 code are few and unless the wire/s has been damaged, replacing the sensor is usually the smartest thing to do.

P0140 BMW P0140 BMW - O2 Sensor Circuit Low Voltage Bank 1 Sensor 2



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
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem
http://engine-codes.com/p0140_bmw.html

In order to get the light out you will have to replace the rear O2 sensor.

From this website:

http://www.obd-codes.com/p0140

P0140 - 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

What does that mean?

The Powertrain control module (PCM) will provide a .45 volt reference voltage to the Oxygen sensor. When the O2 sensor reaches operating temperature, it will generate a voltage that will vary depending on the oxygen content of the exhaust. Lean exhaust generates a low voltage (less than .45V) and rich exhaust generates a high voltage (greater than .45V). O2 sensors on a specific bank marked as "sensor 2" (as this one is) are used to monitor emissions. A Three-Way Catalyst (TWC) system (catalytic converter) is used to control tailpipe emissions. The PCM uses the signal received from Oxygen sensor 2 (#2 indicates aft of catalytic converter, #1 indicates pre-converter) to read efficiency of TWC. Normally this sensor will switch between high and low voltage at a noticeably slower rate than the front sensor. This is normal. If the signal received from rear (#2) O2 sensor indicates that the voltage has "stuck" between .425V to .474 V, the PCM determines this sensor is inactive and this code will set.

Potential Symptoms

Your check engine light(CEL), or malfuction indicator lamp (MIL) will be illuminated. There will not likely be any noticeable drivability problems other than the MIL. The reason is this: The rear or post catalytic converter Oxygen sensor does not affect fuel deliver(this is an exception on Chryslers). It only MONITORS the efficiency of the catalytic converter. For this reason, you will likely not notice any engine trouble.

Causes

The causes for a P0140 code are fairly few. They could be any of the following:

Shorted heater circuit in O2 sensor. (Usually requires replacement of heater circuit fuse in fuse block also)

Shorted signal circuit in O2 sensor

Melting of harness connector or wiring due to contact with exhaust system

Water intrusion in harness connector or PCM connector

Bad PCM

Possible Solutions

This is a fairly specific problem and shouldn't be too difficult to diagnose.

First, start engine and warm up. Using a scan tool, watch the Bank 1, sensor 2, o2 sensor voltage. Normally the voltage should switch slowly above and below .45 volts. If it does, the problem is likely intermittent. You'll have to wait for the problem to surface before you can accurately diagnose.

However, if it doesn

Hi, for the P0140 see http://www.obd-codes.com/p0140. For the P2251 see http://www.elantraxd.com/forums/showthread.php?20258-P2251-O2-sensor

I had this problem with my 05 Trailblazer and it happened around 50k miles. The oxygen sensor needs to be replaced and the part costs about 90 bucks but atleast you will have you're check engine light off.

sounds like seprate issues check for fuel pressure, and spark. the code refers to a poss bad o2 sensor wich would be a seprate issue since o2sensors typically wont keep it from starting, just use alot of gas. good luck