What does it mean?
P1387 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Internal Control Module Altitude Sensor Error .
Symptoms
- MIL on
- Mixture correction goes wrong, so the engine runs rough, especially after large altitude changes
- Reduced power and hesitation on acceleration
- Higher fuel consumption, black smoke on some engines
- Cold start problems and, in some cases, limp mode
Likely causes
- Internal altitude/barometric sensor inside the module reading out of range
- Moisture or condensation inside the module housing
- Low or unstable supply voltage reaching the module
- Poor module ground causing the internal reference to drift
- Corroded or bent pins in the module connector
- Calibration or software mismatch after a module update or replacement
- Internal electronic failure of the control module
How to fix it
- Compare the barometric value reported in live data with the actual atmospheric pressure for the location
- Check battery voltage and charging system stability before anything else
- Perform voltage drop tests on the module power and ground circuits
- Inspect the module and its connector for water intrusion, corrosion and bent terminals
- Confirm the module carries the current calibration for the vehicle
- If the reported pressure stays out of range with the key on and engine off, the internal sensor is at fault
- Reprogram or replace the control module as the final step and relearn the adaptations