---
slug: appendix-a-inspection-standards
title: "DOT Annual Inspection Pass/Fail Standards (Appendix A to 49 CFR Part 396)"
description: "The 15 categories checked in a federal annual inspection, plus the measurement limits that decide pass or fail — brake pushrod stroke, lining thickness, tire tread depth, and steering wheel free play."
track: regulatory
kind: article
isRegulatoryAdjacent: true
publishedAt: 2026-08-10
updatedAt: 2026-09-01
cfr:
  - "49 CFR Part 396 Appendix A"
  - "49 CFR 396.17"
source: https://shopbluecollarparts.com/kb/appendix-a-inspection-standards
license: CC BY 4.0
---

# DOT Annual Inspection Pass/Fail Standards (Appendix A to 49 CFR Part 396)

The standard is **Appendix A to 49 CFR Part 396**, "Minimum Periodic Inspection Standards." Its governing sentence is blunt:

> A vehicle does not pass an inspection if it has one of the following defects or deficiencies.

Fifteen categories follow. This page walks through them and pulls out the measurements, which are the part people actually need to look up.

## The 15 categories

| # | Category | Has measured limits |
|---|---|---|
| 1 | Brake System | ✓ |
| 2 | Coupling Devices | ✓ |
| 3 | Exhaust System | ✓ (buses) |
| 4 | Fuel System | |
| 5 | Lighting Devices | |
| 6 | Safe Loading | |
| 7 | Steering Mechanism | ✓ |
| 8 | Suspension | |
| 9 | Frame | |
| 10 | Tires | ✓ |
| 11 | Wheels and Rims | |
| 12 | Windshield Glazing | ✓ |
| 13 | Windshield Wipers | |
| 14 | Motorcoach Seats | |
| 15 | Rear Impact Guard | ✓ |

Not every category applies to every vehicle. Coupling devices apply where equipped, motorcoach seats to motorcoaches, windshield wipers to power units, and rear impact guards depend on vehicle type, weight, and build date.

## Brake system — the measurements

The brake system is the largest category, and it's the one with the most numbers. It's also the one that requires a **separately qualified brake inspector** under §396.25 — see [who can perform a DOT inspection](/kb/who-can-perform-dot-inspection).

### Pushrod stroke

Appendix A ¶1.a.(5) sets readjustment limits by chamber type. **Any brake stroke exceeding the limit is rejected.**

How it's measured matters as much as the number: **engine off, reservoir pressure of 80 to 90 psi, brakes fully applied.**

Common clamp-type chambers:

| Type | Outside diameter | Standard stroke limit | Long stroke limit |
|---|---|---|---|
| 6 | 4 1/2 in. | 1 1/4 in. | — |
| 9 | 5 1/4 in. | 1 3/8 in. | — |
| 12 | 5 11/16 in. | 1 3/8 in. | 1 3/4 in. |
| 16 | 6 3/8 in. | 1 3/4 in. | 2 in. |
| 20 | 6 25/32 in. | 1 3/4 in. | 2 in. |
| 24 | 7 7/32 in. | 1 3/4 in. | 2 in. |
| 30 | 8 3/32 in. | 2 in. | 2 1/2 in. |
| 36 | 9 in. | 2 1/2 in. | — |

**Two footnotes worth knowing:** type 20 and type 24 chambers *with a 3-inch (76 mm) rated stroke* get 2 1/2 in. rather than 2 in.

Appendix A also tabulates Bendix DD-3, bolt-type, and Rotochamber-type chambers. For any actuator **not** in those tables, ¶1.a.(5)(b) sets the limit at the lesser of 80% of the rated stroke marked on the actuator by the manufacturer, or the readjustment limit marked on the actuator. In other words, you read it off the part.

### Brake lining and pad thickness

Measured **at the shoe center**. Note that the comparison isn't uniform — some limits are "less than," others are "or less," and they sit in adjacent clauses:

| Axle | Brake type | Fails when |
|---|---|---|
| Non-steering | Air drum | less than 1/4 in. |
| Non-steering | Hydraulic and electric drum | 1/16 in. **or less** |
| Non-steering | Air disc | less than 1/8 in. |
| Steering | Drum | less than 1/4 in. |
| Steering | Air disc | less than 1/8 in. |
| Steering | Hydraulic disc and electric | 1/16 in. **or less** |

A lining also fails regardless of thickness if it isn't firmly attached to the shoe, or is saturated with oil, grease, or brake fluid.

**Wedge brakes:** movement of the scribe mark on the lining must not exceed 1/16 in.

### Automatic brake adjusters — a rule, not a measurement

¶1.m.(4) is worth reading closely because it describes a process, not a threshold. Any brake found out of adjustment on initial inspection **must be evaluated to determine why** the automatic adjuster isn't functioning, and the underlying problem corrected before the vehicle can pass.

The regulation says explicitly that it is *not acceptable* to manually adjust automatic brake adjusters without first correcting the underlying problem — and gives examples of what to look for: broken welds, loose mounting hardware, cracked brake drums, worn bushings.

### Low pressure warning

Fails if missing, inoperative, or if it doesn't operate at **55 psi and below, or 1/2 the governor cut-out pressure, whichever is less**.

### Hydraulic systems

Fails if the master cylinder is **less than 1/4 full**, along with a list of leak, hose, and warning-light conditions.

## Tires — tread depth

Measured **at any point on a major tread groove**:

- **Steering axle of a power unit: less than 4/32 in.** fails
- **All other tires: less than 2/32 in.** fails

Steering-axle tires carry a longer list of disqualifiers beyond tread — exposed body ply or belt material, tread or sidewall separation, regrooved tires (with a narrow urban/suburban service exception), boots or blowout patches, mixing bias and radial tires on the same axle, and tube-type radials without radial tube stem markings.

Buses may not be equipped with recapped or retreaded tires at all.

## Steering — wheel free play

On vehicles with power steering, **the engine must be running** when this is measured.

| Steering wheel diameter | Manual system | Power system |
|---|---|---|
| 16 in. | 2 in. | 4 1/2 in. |
| 18 in. | 2 1/4 in. | 4 3/4 in. |
| 20 in. | 2 1/2 in. | 5 1/4 in. |
| 22 in. | 2 3/4 in. | 5 3/4 in. |

Elsewhere in the steering category: any motion other than rotational between a linkage member and its attachment point of **more than 1/4 in.** fails.

## Coupling devices — the tolerances

| Component | Fails when |
|---|---|
| Fifth wheel — pivot bracket pin to bracket | more than 3/8 in. horizontal movement |
| Fifth wheel — slider bracket to slider base | more than 3/8 in. movement |
| Fifth wheel — upper to lower half | horizontal movement exceeds 1/2 in. |
| Pintle hook — horn section | any part reduced by more than 20% |
| Drawbar/towbar eye | any part reduced by more than 20% |
| Drawbar tongue — slider to housing | more than 1/4 in. movement |
| Saddle-mount — upper to lower half | horizontal movement exceeds 1/4 in. |

Fifth wheels also fail on separation that allows light to show through from side to side, and on cracks in the fifth wheel plate — with two exceptions: cracks in the approach ramps, and casting shrinkage cracks in the ribs of a cast fifth wheel body.

## Windshield glazing

A crack, discoloration, or vision-reducing matter fails — but the rule carves out borders and allowances that make it more forgiving than it first sounds.

**Excluded from consideration entirely:** a 2-inch border at the top, a 1-inch border at each side, and everything below the topmost portion of the steering wheel.

**Allowed within the remaining area:**

- Coloring or tinting applied at time of manufacture
- Any crack not over 1/4 in. wide, if not intersected by any other crack
- Any damaged area not more than 3/4 in. in diameter, if not closer than 3 in. to any other such damaged area
- Labels, stickers, and decals (see §393.60 for exceptions)

## Rear impact guard

Two dimensional regimes, and which applies turns on vehicle type, weight, and build date.

**Trailers and semitrailers, GVWR 10,001 lb or more, built on or after January 26, 1998:**

- Horizontal member must extend to within 100 mm (4 in.) of each side extremity, and not beyond either
- Not more than 560 mm (22 in.) above the ground
- Not more than 305 mm (12 in.) forward of the rear extremity
- Cross-sectional vertical height of at least 100 mm (4 in.) across its entire width

**Commercial motor vehicles built after December 31, 1952** (other than the trailers above):

- Not more than 762 mm (30 in.) above the ground
- Must extend to within 457 mm (18 in.) of each side extremity
- Not more than 610 mm (24 in.) forward of the rear extremity

Exceptions live in §393.86, not in Appendix A.

## Appendix A is a floor, not a ceiling

Two things follow from that.

**Part 393 is the underlying standard.** Appendix A repeatedly points back to it — §393.47(e) for pushrod stroke, §393.75(e) for regrooved tires, §393.60 for windshield stickers, §393.86 for rear impact guard exceptions. Category 5 (Lighting Devices) is a single sentence that simply requires everything Part 393 mandates to be operable.

**Passing isn't the end of the obligation.** §396.17(g) requires that parts and accessories be maintained at, or promptly repaired to, these minimums — continuously. And §396.3(a) requires systematic inspection, repair, and maintenance year-round. A vehicle that measured 4/32 in March and 2/32 in September was compliant in March and isn't in September.

## Related

- [Annual DOT inspection requirements](/kb/annual-dot-inspection-requirements) — §396.17
- [Who can perform a DOT inspection](/kb/who-can-perform-dot-inspection) — §396.19 and §396.25
- [What a DOT inspection decal must show](/kb/dot-inspection-decal-requirements) — §396.17(c)(2)

---

*This page summarizes Appendix A to 49 CFR Part 396 as revised through the 2025 edition. It is a partial summary — the tables above omit chamber types and defect criteria for brevity. It is informational only and does not constitute legal or regulatory advice. Consult the current [eCFR](https://www.ecfr.gov/current/title-49/part-396/appendix-Appendix%20A%20to%20Part%20396) for the complete standard.*