Technical Description of OBD-II Trouble Code
Correlation between MAP and Exhaust Pressure
What is the meaning of this?
This generic powertrain diagnostic trouble code (DTC) is commonly found in many OBD-II vehicles, including Ford, GMC, Chevrolet, Dodge, etc. However, it is most frequently observed in Ford Powerstroke Diesel Trucks.
If your OBD-II vehicle has stored a code P006B, it indicates that the powertrain control module (PCM) has detected a discrepancy in the signals between the manifold absolute pressure (MAP) sensor and the exhaust pressure sensor (EPS).
In certain vehicle applications, the MAP sensor may be referred to as a barometric pressure sensor. From my professional experience, only vehicles with diesel engines use exhaust pressure sensors. If there are other codes related to the MAP sensor or exhaust, it is recommended to diagnose and repair those before addressing code P006B.
The MAP sensor measures air density (pressure) in the intake manifold, using units of kilopascal (kPa) or inches of mercury (Hg). The PCM receives these measurements as input voltage signals. Even if the MAP signal is replaced with a barometric pressure signal, it is still measured in similar increments. Diesel-equipped vehicles utilize one or more exhaust pressure sensors to monitor exhaust back pressure. Exhaust back pressure is a valuable indicator of catalyst efficiency, diesel particulate filter efficiency, and NOx filter efficiency. It also plays a critical role in engine performance and emission reduction in modern clean-burning diesel engines.
A code P006B is stored and a malfunction indicator lamp (MIL) may illuminate if the PCM detects voltage input signals (between the MAP sensor and the exhaust pressure sensor) that differ by more than a programmed degree over a certain period of time and under specific circumstances. Exact parameters for code storage can be obtained from a reliable vehicle information source, such as AllData DIY, that is specific to the vehicle in question. In some cases, MIL illumination may require multiple drive cycles with a failure.
Here is an example of a MAF sensor:
How severe is this DTC?
The two sensors associated with this code are crucial for engine performance and efficiency. Therefore, the P006B should be considered severe.
What are some of the symptoms of the code?
Symptoms of a P006B engine code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some troubleshooting steps for P006B?
When diagnosing a code P006B, it is recommended to have a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source.
Visually inspect all related wiring and connectors, paying close attention to wiring harnesses and connectors that are near hot exhaust components and sharp edges associated with exhaust shields. If any damaged or burned areas are found, make the necessary repairs.
The next step is to connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. It is helpful to write down this information as it may assist in the diagnosis. After that, clear the codes and test-drive the vehicle to see if the code reappears.
If the code immediately reappears, use the DVOM to test for reference voltage (typically 5 volts) and a ground at the MAP and exhaust pressure sensor connectors. Simply connect the positive test lead of the DVOM to the reference voltage pin of the sensor connector and the negative test lead to the ground pin, then turn the ignition switch to the ON position.
If reference voltage and a ground are present, reconnect the sensor in question and test its signal circuit with the engine running. Use the air pressure and exhaust back pressure to voltage chart from the vehicle information source to determine if the respective sensors are providing accurate readings. Any sensors that do not reflect the appropriate voltage (according to the MAP and exhaust back pressure to voltage chart) should be considered defective.
If the MAP and exhaust pressure sensor signal circuits show the correct level of input voltage (at the sensor connector), use the DVOM to test the corresponding signal circuit at the PCM connector. If there is an accurate sensor signal at the MAP sensor connector and the exhaust pressure sensor connector, but not at the PCM connector, suspect an open circuit between the PCM and the sensor in question.
The MAP sensor and the exhaust pressure sensor can be tested using the DVOM. Refer to a reliable vehicle information source for the necessary specifications. The DVOM (on the ohms setting) can be used to test the MAP and exhaust pressure sensors while they are disconnected. If either of the sensors does not comply with the manufacturer’s specifications, it should be considered defective.
If all other possibilities have been exhausted, PCM failure or a PCM programming error may be suspected. In such cases, disconnect the PCM (and all related controllers) and test individual system circuits using the DVOM. Follow the diagnostic flow charts, wiring diagrams, and connector pin-out diagrams to test individual circuit resistance and/or continuity.
If no other solutions are found, it may be necessary to consider PCM failure or a PCM programming error.
