Diagnostic Overview
P0069 is generally an intake/boost pressure correlation fault. On a PACCAR MX, the ECM may see manifold pressure, atmospheric pressure, or boost-related data that does not agree under key-on or running conditions. This can affect turbo control, fueling, EGR operation, and derate decisions. On PACCAR MX engines, confirm the exact definition with DAVIE4, the engine serial number, emissions year, and current calibration because code meanings and troubleshooting trees can vary.
Likely Causes
Faulty intake manifold pressure sensor; blocked sensor port; damaged wiring; boost leak; charge-air cooler leak; incorrect barometric pressure reading; intake restriction; sensor contamination.
What To Check First
Compare barometric and manifold pressure key-on/engine-off, inspect the intake pressure sensor and port, pressure-test the charge-air system, and verify boost readings under load.