will 393.25(b) put my truck out of service
No, not automatically. Across our 13 million inspection records, 393.25(b) citations resulted in an out-of-service placement only 8.0% of the time (42 out of 528 all-time citations). That is significantly lower than the national FMCSR average of 31.4%, making this a relatively low-severity finding in terms of immediate roadside enforcement. However, if a second violation is stacked during the same inspection, the inspector may make a different call.