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+--- Thread: CECU cruise control rationality check (/showthread.php?tid=10796)
CECU cruise control rationality check - cesar034 - 10-24-2026
Good day everyone, I wanted to reach out and see if anyone has dealt with this issue, I have a
2013 Peterbilt 386 with a Cummins isx15. Cruise control will not function, engine brake works but
On ESA I get a fault code 59631 for cruise control rationality.
Looked it over and the module wants clutch and brake to both be applied before cruise can be engaged
But I do that and I can see the values on insight for clutch and brake go from released to depressed but
The same fault keeps appearing I've tried different variations in the parameters between the multiplex settings and I updated the CECU but still have no had any luck. Any help would be appreciated thank you guys.
RE: CECU cruise control rationality check - Rawze - 10-24-2026
== Maybe disconnect batteries for 30 minutes to force reset the cab controller?. - Paccar chassis controllers in general are known to need a hard reset once in a while to solve ghost issues.
== Check all fuses in the fuse panel for discolored fuse blades (even though they might still be good) and replace any that are not shiny new looking?. - Tarnished fuses will often cause a few tenths voltage drop on the cab controller or other devices and cause them to act up as a truck gets older.