Technical Description of OBD-II Trouble Code
Correlation Between MAP and Mass or Volume Air Flow in Bank 2
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is applicable to various OBD-II vehicles, including Land Rover, Ford, Alfa Romeo, Toyota, and others.
A stored code P00B8 indicates that the powertrain control module (PCM) has detected a discrepancy in the signals between the manifold absolute pressure (MAP) sensor and the mass or volume air flow sensor (MAF/VAF) for engine bank two.
Bank 2 refers to the engine bank that does not contain the number one cylinder. To determine the location of the #1 cylinder for a specific vehicle, consult a reliable vehicle information source. This code should only be exhibited by vehicles equipped with multiple throttle body openings, one per engine bank.
The MAP sensor measures the air density (pressure) in the intake manifold and provides the PCM with a voltage signal. This voltage signal is received by the PCM as either kilopascal (kPa) units or inches of mercury (Hg). In some cases, MAP is used as a substitute for barometric pressure and measured in similar increments. When the internal combustion engine operates at peak efficiency, it creates a strong vacuum that should be restricted to the throttle body opening/s. The throttle plate, controlled by the driver under acceleration, and the idle air control (IAC) valve when the engine is at idle, regulate this vacuum. The vacuum draws in the air necessary for each combustion cycle.
A precise fuel to air ratio is crucial for achieving maximum fuel efficiency and minimizing harmful exhaust emissions in mass-produced vehicles. As the throttle plate/s open, the MAF or VAF sensor/s measure the air entering the intake manifold. The PCM calculates fuel delivery and ignition timing strategy based on data from these sensors. The air passing through these devices is referred to as metered air. However, if air is involuntarily introduced to the engine (vacuum leaks), it can contribute to excessively lean conditions (too much air or not enough fuel) and is called unmetered air.
There are two basic types of air metering devices:
MAF Sensor
This type of sensor is commonly used in domestic vehicles. It consists of one or more thermal resistors suspended in the sensor housing, allowing air to flow across them. One thermal resistor monitors MAF, while the other measures intake air temperature (IAT). Hot wire MAF sensors use voltage applied directly to a single resistor to monitor the intake air flow. As the ambient air flow across the resistor increases, the temperature of the resistor decreases, resulting in a drop in resistance level. These changes in resistance level produce voltage variations that the PCM interprets as the amount of metered air entering the engine intake manifold. Cold wire MAF sensors are similar to hot wire sensors and also use a pair of thermal resistors. The first measures ambient air temperature, while the second measures incoming air as the throttle plate opens. The PCM compares input voltage signals from each resistor to determine the amount of metered air drawn into the engine.
VAF Sensor
The key difference between the MAF and VAF is that the VAF has a door or flap that opens as air is drawn into the intake. This type of air metering device is primarily used in European vehicles. At idle, the spring-loaded flap is closed, and when the throttle is opened, the door is forced open. The action of the door/flap on its hinge actuates a potentiometer that sends a voltage signal to the PCM. The PCM interprets variations in potentiometer voltage as the degree of metered air entering the intake.
A code P00B8 will be stored, and a malfunction indicator lamp (MIL) may illuminate if the PCM detects voltage signals between the MAP sensor and the MAF/VAF sensor (Bank 2) that differ by more than a programmed degree. MIL illumination may require multiple ignition cycles with a failure.
An example of a MAF sensor:
What is the severity of this DTC?
Due to the critical role of fuel delivery and ignition timing in engine performance and efficiency, the P00B8 code should be considered severe and addressed accordingly.
What are some of the symptoms of the code?
Symptoms of a P00B8 engine code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P00B8 troubleshooting steps?
To diagnose a code P00B8, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), a manual vacuum pressure gauge, and a reliable vehicle information source.
Before diagnosing any MAP sensor-related code, perform a manual engine vacuum pressure test using the vacuum pressure gauge. If the engine does not generate sufficient vacuum, it must be repaired before proceeding with the diagnosis.
Inspect the engine and all air inlet pipes for signs of cracking or breakage, and make any necessary repairs. Vacuum leaks can contribute to the conditions that caused the P00B8 code to be stored.
If the engine is in good working order and there are no vacuum leaks, visually inspect all related wiring and connectors. Make any required repairs.
Connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Take note of this information as it may assist in the diagnosis. Clear the codes and test-drive the vehicle to see if the code is reset.
If the code is immediately reset:
If the sensors comply with manufacturer’s specifications:
If reference voltage and a ground are detected:
If the sensor signal input voltage (at the sensor connector) reflects the correct degree of voltage:
If all sensors and circuits are within specifications, suspect PCM failure or a PCM programming error.
