Fault code lookup
Type what is on the dash. SPN in the first box, FMI in the second — or paste a P-code or a reefer alarm number into the first box and leave the second empty.
Reading the number off the dash
On most Class 8 dashes the fault appears as a pair: a suspect parameter number telling you which measurement went wrong, and a failure mode identifier telling you how. Some displays add a source address, which identifies the module that reported it — a code from the engine ECM and the same code from the aftertreatment controller are different problems.
Manufacturers also publish their own code numbers on top of the J1939 pair. A Freightliner dash may show a proprietary fault number while the underlying network message is a standard SPN and FMI. Where we know both, both are searchable here.
Full reference: what each FMI actually means.