SPN 4364 — SCR conversion efficiency low

SPN 4364 is the parameter the ECM is flagging on Mack engines. The FMI that comes with it tells you how it failed. Each failure mode below has its own causes and its own test order — do not treat them as the same repair.

FMI 18 · Data valid but below normal operating range — moderately severe level

SCR conversion efficiency low

Real reading, clearly low. The stage before a derate or shutdown.

Full diagnosis for SPN 4364 FMI 18 What FMI 18 means

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