Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
This code indicates that the PCM has detected a manifold air pressure sensor signal voltage that is either abnormal for the current amount of engine load and throttle angle or fails to correlate with the manifold pressure sensor.
Code Set Parameters
An incorrect manifold air pressure sensor voltage reading has been detected for a period exceeding four-seconds continually (most manufacturers). This reading is measured against reference voltage for the particular vehicle application.
Symptoms include sag, stumble, or hesitation upon acceleration, decreased fuel efficiency, an illuminated service engine soon light, and a stored trouble code.
Common causes of this code include a poor running engine that needs to be repaired, engine backfire or severe/multiple misfires, clogged catalytic converter/s, faulty PCM, mass airflow sensor, manifold air pressure sensor, barometric pressure sensor, or throttle position sensor. PCM failure is rare.
Often expensive mass airflow sensors and barometric pressure or manifold air pressure sensors are replaced when a simple cleaning of the MAF “hot wire” could rectify the condition. Corroded wiring and/or connectors have also been reported by technicians.
- The barometric pressure sensor and manifold air pressure sensor work in conjunction to provide input data to the PCM regarding the degree of air pressure (or vacuum) in the intake manifold
- The PCM uses the data to calculate fuel delivery strategy and control the air/fuel ratio
- The barometric pressure sensor, in particular detects changes in atmospheric pressure and also the vehicle’s geographic distance above sea level
- Changes in sensor voltage are interpreted by the PCM as variations in intake manifold pressure as compared to ambient pressure.
Several tools may be needed to successfully diagnose this code if no exhaust leaks are detected
- A suitable scanner, a digital volt/ohmmeter, and a manufacturer’s service manual (or equivalent) will help to perform a thorough diagnosis
Begin with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- Continue by clearing the code and operating the vehicle to see if it returns
- This will help to determine whether or not the malfunction is intermittent
After the codes are cleared, test drive the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
If there are mass airflow, manifold air pressure, or engine misfire codes present, diagnose those conditions before attempting to diagnose this code
Determine whether there is a malfunction in MAF/BPS system circuitry, a problem with unmetered air entering the engine, or a problem with an insufficient air supply to the engine
- Make sure that the engine is in good working order, with no misfires, lean conditions, etc
- Repair these conditions before attempting to diagnose this code
- Check for a clogged air filter element, broken, pinched or disconnected air inlet pipe, clogged catalytic converter/s, or a vacuum leak prior to beginning an electrical diagnosis
- If these items are found to be in proper working order, check for power and ground at the barometric pressure and manifold air pressure sensors
- If reference voltage and ground are detected at the sensor connector, test the sensor/s using the manufacturer’s pressure to hertz chart
- If the sensor fails to comply with the manufacturer’s specifications, replace the sensor as required
- Clear the codes and test drive the vehicle to ensure that the repair was successful.
If the sensor/s check out, prepare to perform a continuity and resistance test by disconnecting the connector from all related control modules
- Test all related circuits for continuity and resistance and repair or replace all defective circuits as required
- Clear the codes and retest the system to make sure that your repair was successful
If all sensors and circuitry coincide with the specifications from the service manual, continue by visually inspecting the vane or hot wire of the MAF itself for signs of dirt or other debris
- This can be removed by carefully using an approved chemical cleaner and a cotton swab, then blowing dry with low pressure compressed air.
If the symptoms and codes persist after these steps are taken, suspect a defective PCM
- Keep in mind that PCM failure is rare and will require reprogramming