What does it mean?
P1408 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: MAP Sensor Circuit Malfunction .
Symptoms
- MIL on
- Rough idle, surging or hunting idle speed
- Hesitation and poor acceleration, black smoke under hard throttle
- Noticeably higher fuel consumption
- Hard starting and occasional stalling
- Emissions test failure
Likely causes
- Cracked, disconnected or blocked MAP vacuum hose
- MAP sensor contaminated with oil, fuel or carbon
- Open, shorted or high resistance signal, reference or ground wiring
- Corroded connector at the sensor
- Failed MAP sensor element
- Large intake vacuum leak producing an implausible pressure value
- Control module input circuit fault
How to fix it
- With the key on and the engine off, compare the MAP reading with the local barometric pressure, the values should match closely
- Watch MAP in live data at idle and during a snap throttle, the value must react instantly
- Inspect the vacuum hose and replace it if cracked, oil soaked or blocked
- Check for 5 volts reference and a clean ground at the sensor connector
- Test signal wire continuity back to the control module
- Apply a hand vacuum pump to the sensor and confirm a smooth linear change in the signal
- Replace the MAP sensor if it does not track applied vacuum, and repair any intake leak found