Diagnostic Overview
CAT fault code 2629-03 is commonly associated with a turbocharger-related pressure or air-system sensor circuit voltage above normal. The exact sensor name depends on the engine and application, but FMI 3 generally points to an electrical high-voltage condition. The ECM may receive an implausible air-system reading and may limit boost or power.
Likely Causes
Short to voltage; failed turbo/air pressure sensor; open ground; damaged harness; corroded connector; wrong sensor; water intrusion.
What To Check First
Confirm the exact SPN 2629 description in Cat ET, inspect the sensor connector, check reference and signal voltage, and compare the reading to expected pressure.