Diagnostic Overview
CAT fault code SPN4112 is best read as SPN 411 FMI 2. This generally indicates EGR differential pressure or EGR flow data that is erratic, intermittent, or not plausible. The ECM is seeing a signal that does not match engine speed, load, boost, or expected EGR operation. This is often caused by sensor tube problems or wiring issues, but carbon buildup and EGR valve problems can also create unstable readings.
Likely Causes
Erratic EGR pressure signal; plugged or leaking sensor tubes; moisture in tubes; faulty sensor; loose connector; damaged wiring; carbon buildup; unstable EGR valve operation.
What To Check First
Inspect EGR pressure tubes for blockage or moisture, wiggle-test the harness, compare live data during commanded EGR operation, and inspect the EGR valve and cooler.