P02B2 Cylinder 7 Fuel Trim at Max Limit
OBD-II Trouble Code Technical Description
Cylinder 7 Fuel Trim at Max Limit
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) and typically applies to all gasoline OBD-II vehicles. That may include but is not limited to vehicles from Land Rover, Mazda, Jaguar, Ford, Mini, Nissan, GM, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
A stored P02B2 code means that the powertrain control module (PCM) has detected an extremely lean condition in a specific engine cylinder, in this case it's cylinder #7.
The PCM utilizes the fuel trim system to increase or decrease fuel delivery as required. Input signals from the oxygen sensors provide the PCM with the data required to adjust fuel trim. The PCM uses variations in fuel injector pulse width modulation to effect air/fuel ratio changes.
Short term fuel trim is calculated constantly by the PCM. It fluctuates rapidly and is one of the key factors in calculating long term fuel trim. Every vehicle has minimum and maximum fuel trim percentage parameters programmed into the PCM. The parameters for short term fuel trim are much broader than the parameter specifications for long term fuel trim.
Small variations in fuel trim, typically measured in positive or negative percentage, are normal and will not cause a code P02B2 to be stored. Maximum fuel trim parameters (positive or negative) are normally in the twenty-five-percent range. Once this maximum threshold has been exceeded, a code of this type will be stored.
When the engine is functioning at optimum efficiency and there is little need to increase or decrease the amount of fuel delivered to each cylinder, fuel trim should reflect between zero and ten percent. When lean exhaust conditions are detected by the PCM, fuel must be increased and fuel trim will reflect a positive percentage. If the exhaust is too rich, the engine needs less fuel and fuel trim should reflect a negative percentage.
See also: Everything you want to know about fuel trims.
OBD-II vehicles will need to establish a pattern for long term fuel trim strategy and this will require multiple ignition cycles.
Fuel trim graphs as shown by OBD-II scan tool:
What is the severity of this DTC?
The P02B2 should be classified as severe because a lean fuel condition may result in catastrophic engine damage.
What are some of the symptoms of the code?
Symptoms of a P02B2 trouble code may include:
Diminished engine performance Delayed engine startup The presence of stored lean exhaust codes Misfire codes may also be storedWhat are some of the common causes of the code?
Causes for this P02B2 fuel trim code may include:
Defective/leaking fuel injector Bad fuel pump Engine vacuum leak (including EGR valve failure) Faulty oxygen sensor Mass air flow (MAF) or Manifold Air Pressure (MAP) sensor failureWhat are some P02B2 troubleshooting steps?
If there are MAF or MAP related codes present, diagnose and repair those before attempting to diagnose this P02B2 code.
I would begin my diagnosis with a general inspection of the engine intake manifold area. My focus would be on vacuum leaks. First, I would listen for the sound (hissing) of a vacuum leak. I would be checking all hoses and plastic lines for signs of cracking or collapse. The PCV lines are a common source of vacuum leaks. Also, check the edges of the intake for signs of gasket failure. Secondly, I would examine the fuel injector in question (cylinder #7) for signs of fuel leakage. If the injector is wet with fuel, suspect that it has failed.
If no obvious mechanical issues are discovered in the engine bay, there are several tools that will be required to continue your diagnosis:
A diagnostic scanner A dRead: 40
