What does this OBD II code mean?
This generic OBD2 code is set when the Powertrain Control Module (PCM) constantly senses a rich mixture with little or no change over time.
This particular code is pointing out the bank 1, in other words, the bank of cylinders containing cylinder #1. The sensor 3 tag is indicating the downstream O2 sensor located just after the last catalytic converter.
Why does this OBD II code appear?
Post catalyst oxygen sensors normally cycle between rich and lean mixtures at a slow rate. Their waveform is somewhat flat but the value is never constant. When the PCM detects a bias toward a rich state or worse yet, a fixed value close to 0.9V, it initiates the compensation protocol and turns on the CEL.
The OBD2 code P2275 is stored in memory when the PCM detects a condition like the explained above where the bank 1, sensor 3 is constantly reporting a rich mixture during a given period of time, even after fuel delivery compensation.
What symptoms may occur with this OBD II code?
Assuming a rich mixture is indeed present, expect the typical symptoms from such condition:
- CEL lit. The Check Engine Light will turn on after few driving cycles to alert the driver about the situation.
- Poor fuel economy.
- Possible misfires and/or spark knock.
- You may have rough idling.
- Possible hesitation during acceleration.
- A strong gasoline smell on the exhaust and/or a “rotten eggs” smell.
- Depending on the vehicle year a slight rise in engine temperature may occur.
- Under extreme circumstances, a black smoke may be noticeable coming out the exhaust pipe.
What are the causes that trigger this OBD II code?
There're many factors that could cause a rich mixture condition including among others the following:
- Damaged, burnt, corroded, open or shorted O2 sensor wiring.
- Worn, corroded, burnt, disconnected or bent O2 wiring harness connector pins.
- High fuel system pressure caused by the fuel pump or faulty/deficient fuel pressure regulator
- Excess fuel caused by stuck fuel injectors or even dirty fuel injectors not pulverizing fuel as expected (deficient fuel spray).
- Faulty or deficient upstream oxygen sensor.
- Faulty or deficient downstream oxygen sensor.
- Even when unlikely, a defective PCM cannot be discarded.
Please notice that possible causes are based on the assumption that only trouble code P2275 is stored in memory.
Diagnostic strategy for troubleshooting this OBD II code
Warning: If any other code directly related to the bank 1 oxygen sensor 1 is present then you must start diagnosing and solving those codes first. The same recommendation applies to MAF sensor trouble codes.
It's highly recommended starting the diagnostic process with the usual information gathering:
- With the help of a professional OBD2 scan tool, preferably one with OEM capabilities, take note of all data trouble codes in memory, including pending codes.
- Take note of freeze frame information (if present).
- Query the vehicle owner about what, when and where the failure occurs. Does it happen with the engine hot? Cold? Under load? All the standard questions.
- Take note of the vehicle VIN and find a reliable source of technical reference.
Once you are done, the next step is discarding an intermittent condition.
- Using your scan tool clear DTC memory.
- Perform a complete driving cycle according to OEM procedures.
If the code P2275 disappears then inform the owner about the intermittent nature of the code and explain that further testing with the code present will be required. If the code does appear then continue to the testing stage, consisting in discarding the possible causes of the problem.
IMPORTANT: the diagnostic procedure explained in this section should be taken as a guideline. Always refer to specific OEM procedures when possible.
The workflow for the diagnostic process is:
- The tests should be executed in sequential order, in other words, complete step 1 before going to step 2 and so on.
- Repair, fix, or replace any component if you suspect is not in good condition.
- If any repair, fix, reprogramming or component replacement is made during any step then you should clear DTC memory and repeat the whole KOER driving cycle.
- If the DTC appear again then you should continue to the next step.
- If the DTC does not appear again after completing the KOER tests then you can assume the problem is fixed, in that case, continuing with the remaining steps would be optional.
The diagnostic process for the code P2275 is as follows:
- Sensor harness wiring and connector: carry out an exhaustive visual inspection of MAF sensor and oxygen sensor wiring and connectors. Pay special attention to burnt, corroded or deteriorated wiring and/or connector. Unplug each sensor and check for corrosion, damage, bent pins, etc.
- Electrical tests: with the help of a digital volt-ohm meter (DVOM) and the adequate wiring diagram perform a KOEO check on the MAF and O2 sensors. Verify supply and/or reference voltage, electrical resistance, continuity, current and ground integrity. Compare the obtained values with the appropriate OEM literature.
- Fuel system delivery: carry out a manual fuel pressure reading using a proper fuel pressure gauge and adapters. This is crucial, even if the scanner is reporting the fuel pressure. If the fuel pressure is above its normal value then perform an extensible fuel system test starting with the fuel pump followed by the fuel pressure regulator and fuel injectors performance.
- Upstream oxygen sensor: some manufacturers include built-in tests that help in the process of diagnosing the O2 sensor, others not. Refer to the proper literature in order to perform a complete sensor diagnostic. Replace if needed. As usual, after any repair clear the DTC memory, repeat KOER driving cycle and check if the code persists. If the code appears again then continue with the next step.
- Downstream oxygen sensor: most vehicle manufacturers use traditional oxygen sensors (instead of A/F sensors) for the post-catalyst monitoring. This opens you the possibility of performing the sensor test using a DVOM, an oscilloscope or a scan tool. Refer to the proper OEM literature in order to decide what is the best approach. Replace the O2 sensor if necessary and repeat all KOER tests before continuing.
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Problems with the powertrain control module: the most unlikely cause for this code is a faulty PCM or a corrupted program. Yet, if you are completely certain that all prior tests passed then you must remove the PCM and check it, reprogram it or replace it as necessary.
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