Manifold Absolute Pressure - Barometric Pressure Correlation
This code indicates that the PCM has detected a correlation problem between the manifold air pressure sensor and barometric pressure sensor signal voltage.
Code Set Parameters
An incorrect MAF/BPS voltage reading has been detected for a period exceeding four-seconds continually. This reading is measured against the manufacturer’s reference voltage.
Symptoms may include hesitation during acceleration, decreased fuel efficiency, and service engine soon lamp illumination.
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, MAP, BPS, or throttle position sensor. PCM failures are rare.
Often manifold air pressure and barometric pressure sensors are replaced when a simple cleaning of the mass air flow sensor “hot wire” could rectify the condition. Corroded wiring and/or connectors have also been reported by technicians.
- Many vehicles equipped with OBD-II diagnostic systems use both a manifold air pressure sensor and a barometric pressure sensor to monitor and control engine operation
- Manifold air pressure sensors (as the name implies) monitor manifold air pressure during varying RPM levels and driving conditions
- The sensors are of a variable resistance type with voltage readings being input to the PCM, constantly while the key is in the run position or when the engine is running
- The barometric pressure sensor also inputs data into the PCM regarding the vehicle’s distance above sea level
- If the manifold air pressure is not within a specified amount as compared to the vehicle’s distance above sea level, engine temperature, engine RPM level, and engine load, a code will be stored and a malfunction indicator lamp will be illuminated
- By the same token, If the barometric pressure sensor fails to comply with manufacturer’s specs in regard to the distance above sea level and manifold air pressure data, a code will be stored and a service engine soon lamp illuminated.
Determine whether there is a malfunction in MAP/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 vacuum leaks prior to beginning an electrical diagnosis
- Visually inspect the vane or hot wire of the MAF itself for signs of foreign dirt or other debris
- This can be removed by carefully using an approved chemical agent and a cotton swab, then blowing dry with compressed air
A scanner or code reader and a digital volt/ohmmeter will be very helpful in diagnosing this code successfully.
Begin your diagnosis with a visual inspection of all MAP/BPS system circuitry and electrical connectors
- Don’t forget to inspect vacuum hoses for holes, cracks, or other discrepancies
- Repair or replace damaged, disconnected, or corroded components and/or wiring/connectors as required
- Retest the system to ensure that repairs were successful.
If system components and circuitry appear to be in proper working order, connect the scanner to the diagnostic connector of the vehicle and turn the key to the run position
- Note any stored codes and freeze frame data
- This may prove to be instrumental in diagnosing this condition if it proves to be intermittent
Now, clear the codes and test drive the vehicle if possible
- Address the codes that are reset, if any
- If no codes are reset, you may have an intermittent condition and it could be virtually impossible to diagnose correctly
- In rare instances, a condition may have to be allowed to worsen before a successful diagnosis can be made.
If the code returns immediately, obtain a wiring schematic and/or a connector view for the MAP and BPS system circuitry of the vehicle
- Check for voltage and ground signals at the respective sensors and compare your findings with manufacturer’s specifications
- Repair open, shorted, or disconnected circuits as necessary
- If there is no voltage present, check system fuses and relays
- If the ground is not present, look for loose or corroded ground straps and wires near the battery and engine block
Most systems use a constant reference voltage supply to the sensor (typically 5-volts) and a ground wire; with the sensor providing varying resistance levels and altering input voltage to the PCM
- The PCM reads these varying voltage levels as changes in either manifold air pressure or barometric pressure
- If the sensor electrical connector voltage is in line with manufacturer’s specifications, use the digital volt ohmmeter to test sensor resistance and compare your findings with manufacturer’s specs
- Replace the sensor/s if resistance levels do not coincide with manufacturer’s specifications.
If the sensor, wiring, and connectors check out, perform a circuit resistance and continuity test
- Always disconnect any related computerized controllers from the circuit prior to testing resistance
- Repair or replace any shorted or open circuits and retest the system to make sure that it is repaired correctly.
If the system circuitry appears to be normal, suspect a defective PCM
- Remember that PCM failure is rare.