What 393.51(b) means in plain language
Your steering wheel should have a small amount of play—that's normal. But there's a limit. If the amount of movement before the wheels actually turn is too much for your steering system type, you've violated 393.51(b).
This isn't about the wheel spinning freely or being loose in your hands while driving. It's specifically about the dead zone—the distance you can turn the wheel before the front tires respond. Different steering systems (manual, power, or others) have different allowable limits, and inspectors measure this using standardized procedures. If your steering wheel play exceeds what's permitted for your truck's setup, the citation follows.
Why it matters: excessive steering wheel play degrades your ability to make small, precise corrections at highway speed. It can hide wear in tie rods, steering gearbox components, or power steering systems that, if left unchecked, could fail entirely.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.51(b) has generated 93 all-time citations. In the last 12 months, we recorded zero citations; in the last 90 days, zero citations. This code ranks #1440 out of 3,036 FMCSR codes by citation volume—a rarity in roadside enforcement.
When 393.51(b) is cited, however, the outcome is severe: our data shows a 100.0% out-of-service rate. Every single truck cited for this violation was placed out of service. That contrasts sharply with the all-FMCSR average of 31.4%. The difference is striking: inspectors do not issue this citation lightly, and when they do, your truck does not continue down the road.
Who gets cited most
Our inspection records do not include state-level breakdowns in sufficient detail for this violation to identify a clear top-three state distribution. However, our data shows fleets such as DKM LOGISTICA SA DE CV (USDOT 3118976) with 5 citations all-time—the highest count in our database for this code. ALIMENTS INC (USDOT 3434528) follows with 2 citations. The remaining carriers in our records each have 1 citation. This pattern suggests that 393.51(b) citations are scattered widely rather than concentrated in any single fleet or region.
Vehicle make data is more informative: ISUZU trucks account for 24 of the 93 all-time citations, followed by FORD with 19 and INTERNATIO with 13. Older or medium-duty trucks appear in our data more frequently than Class 8 linehauls, which may reflect inspection patterns on smaller carriers or regional routes.
How severe is this compared to similar codes
In the vehicle-maintenance category, 393.51(b) is an outlier in both rarity and OOS consequence. Compare it to three peer codes:
- 393.9(a) — Inoperable required lamps: 660,737 citations with a 15.4% OOS rate. This is cited far more frequently but results in out-of-service placement only one-seventh as often.
- 396.3(a)(1) — Inspection/repair/maintenance general: 236,919 citations with a 45.3% OOS rate. More common than 393.51(b) and more likely to trigger OOS, yet still not at the 100% threshold.
- 393.47E — Slack adjuster defective: 180,363 citations with a 0.0% OOS rate. Cited 1,939 times more frequently than 393.51(b) but almost never results in placement out of service.
The 100.0% OOS rate for 393.51(b) places it in a small group of violations that inspectors treat as immediate safety showstoppers. When an inspector finds excessive steering wheel play, they do not allow continued operation under any circumstance.
How to avoid it
Before each trip:
- Perform a steering system pre-trip inspection. Turn the wheel fully left and fully right while the truck is parked, feeling for binding, noise, or unusual resistance. Note any changes from your baseline feel.
- Check tie rod ends and draglink components. Look for visible wear, loose fasteners, or movement in the steering linkage. These are the most common sources of excessive play.
- Test power steering fluid level and condition. Low or degraded fluid can mask or cause play issues. Top up to the cold-fill mark on the reservoir.
- Listen for groaning or whining in the steering system. A failing power steering pump or gearbox often announces itself with noise before play becomes measurable.
During your shift:
- Notice any change in how the steering feels. Increased play, a mushy response, or a need to correct more often all signal developing wear. Report it to your dispatcher or maintenance immediately rather than waiting for an inspection.
- Avoid harsh over-correction or steering shock loads. Aggressive turns at speed or hitting a pothole hard while turning can accelerate wear in tie rods and the steering gearbox.
At the shop:
- Request a formal steering system inspection if you suspect play is increasing. Technicians can measure play accurately using a steering wheel rotameter and compare it to manufacturer specs for your truck model.
- Replace tie rods, draglinks, or steering gearbox components before they become excessive. These wear parts are consumable; catching them early avoids a roadside citation and keeps your truck safe.
Our data shows that vehicles with 393.51(b) citations span multiple makes, with ISUZUs and FORDs appearing most often. Regardless of your truck's brand, the root cause is the same: worn steering linkage or gearbox components that must be addressed during maintenance, not ignored until an inspector measures the play.