OBD-II Trouble Code Technical Description
The fuel trim for cylinder 8 is at its maximum limit.
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) that applies to all gasoline OBD-II vehicles, including Land Rover, Mazda, Jaguar, Ford, Mini, Nissan, GM, etc. The exact repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored P02B6 code indicates that the powertrain control module (PCM) has detected an extremely lean condition in cylinder #8.
The PCM uses the fuel trim system to adjust fuel delivery as needed. Input signals from the oxygen sensors provide the PCM with the necessary data to adjust fuel trim. The PCM uses fuel injector pulse width modulation to change the air/fuel ratio.
The PCM constantly calculates short term fuel trim, which fluctuates rapidly and is a key factor 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 broader than those for long term fuel trim.
Small variations in fuel trim are normal and will not trigger a P02B6 code. Maximum fuel trim parameters are typically in the twenty-five-percent range. Once this threshold is exceeded, a code of this type will be stored.
When the engine is operating efficiently and there is no need to adjust the fuel delivery, fuel trim should be between zero and ten percent. If the PCM detects a lean exhaust condition, fuel must be increased and fuel trim will show a positive percentage. If the exhaust is too rich, the engine requires less fuel and fuel trim will show a negative percentage.
See also: Everything you want to know about fuel trims.
OBD-II vehicles need to establish a pattern for long term fuel trim strategy, which requires multiple ignition cycles.
Fuel trim graphs as shown by OBD-II scan tool:
What is the severity of this DTC?
The P02B6 code should be classified as severe because a lean fuel condition can cause catastrophic engine damage.
What are some of the symptoms of the code?
Symptoms of a P02B6 trouble code may include:
What are some of the common causes of the code?
Possible causes for this P02B6 fuel trim code may include:
What are some P02B6 troubleshooting steps?
If there are MAF or MAP related codes present, diagnose and repair those before attempting to diagnose this P02B6 code.
I would start by inspecting the engine intake manifold area for any signs of vacuum leaks. Check all hoses and plastic lines for cracking or collapse. The PCV lines are a common source of vacuum leaks. Also, inspect the intake edges for gasket failure. Additionally, examine the fuel injector for cylinder #8 for signs of fuel leakage.
If no obvious mechanical issues are found in the engine bay, you will need several tools to continue your diagnosis:
Next, connect the scanner to the vehicle diagnostic port. Retrieve all stored codes and freeze frame data, and write them down for later use. Clear the codes and test-drive the vehicle to see if any codes are reset.
Access the scanner data stream and observe oxygen sensor operation to determine if a lean exhaust condition actually exists. Narrow the data stream to include only pertinent data for faster response time and more accurate readings.
If an actual lean exhaust condition is present:
Step 1
Use the fuel pressure gauge to test fuel pressure and compare it with the manufacturer’s specifications. If fuel pressure is within specs, proceed to Step 2. If fuel pressure is below the minimum specifications, use the DVOM to test the fuel pump relay and fuel pump voltage. If the fuel pump is receiving an acceptable level of voltage, remove the fuel filter and check for clogs. Replace the filter if it is clogged, or suspect fuel pump failure if it is not.
Step 2
Access the connector for the injector in question and use the DVOM (or a noid lamp if available) to test for injector voltage and a ground pulse from the PCM. If no voltage is detected at the injector connector, proceed to Step 3. If voltage and a ground pulse are present, reconnect the injector and listen to it with the engine running using a stethoscope or similar device. An audible clicking sound should be heard at regular intervals. If the sound is absent or intermittent, suspect that the injector for the cylinder in question has failed or is clogged, and consider replacing it.
Step 3
Most modern fuel injection systems provide a constant supply of battery voltage to each fuel injector, with the PCM supplying a ground pulse at the appropriate time to complete the circuit and spray fuel into the cylinder. Use the DVOM to test system fuses and relays for battery voltage. Replace any faulty fuses or relays. Test system fuses with the circuit under load.
Be cautious when testing or replacing high pressure fuel system components.
