FMVSS 138: Tire Pressure Monitoring Systems explained.

What FMVSS 138 says it is for

The eCFR heads this section "Standard No. 138; Tire pressure monitoring systems." Under 49 CFR part 571, the Federal Motor Vehicle Safety Standards are the numbered standards that set safety performance requirements for motor vehicles and equipment. The text below is quoted from 571.138 as current through October 29, 2026.

This standard specifies performance requirements for tire pressure monitoring systems (TPMSs) to warn drivers of significant under-inflation of tires and the resulting safety problems.

What it applies to

The application section of the standard says:

This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and buses that have a gross vehicle weight rating of 4,536 kilograms (10,000 pounds) or less, except those vehicles with dual wheels on an axle, according to the phase-in schedule specified in S7 of this standard.

Applicability is decided by the text of the standard as written, including any exclusions it lists, and by the date-specific rules in it. This page does not decide whether a particular vehicle or item is covered.

How the standard is organized

The eCFR text of 571.138 has these top-level sections:

• S1: Purpose and scope
• S2: Application
• S3: Definitions
• S4: Requirements
• S5: Test conditions
• S6: Test procedures
• S7: Phase-in schedule

In all, the text has 29 numbered headings. Use the finder above to search them; for example, a search for "test" lists the headings that mention tests.

Second-level headings at a glance

These are the numbered sub-sections one level below the top, in order (first 15 of 15):

• S4.1 General
• S4.2 TPMS detection requirements
• S4.3 Low tire pressure warning telltale
• S4.4 TPMS malfunction
• S4.5 Written instructions
• S5.1 Ambient temperature
• S5.2 Road test surface
• S5.3 Vehicle conditions
• S7.1 Vehicles manufactured on or after October 5, 2005, and before September 1, 2006
• S7.2 Vehicles manufactured on or after September 1, 2006, and before September 1, 2007
• S7.3 Vehicles manufactured on or after September 1, 2007
• S7.4 Calculation of complying vehicles
• S7.5 Vehicles produced by more than one manufacturer
• S7.6 Small volume manufacturers
• S7.7 Final-stage manufacturers and alterers

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.138, in the order the standard presents them. Long paragraphs are shortened where marked with [...]; the eCFR has the complete text, tables and figures, which this page omits.

S4.1 General. To the extent provided in S7, each vehicle must be equipped with a tire pressure monitoring system that meets the requirements specified in S4 under the test conditions specified in S5 and the test procedures specified in S6 of this standard.

S4.2 TPMS detection requirements. The tire pressure monitoring system must: (a) Illuminate a low tire pressure warning telltale not more than 20 minutes after the inflation pressure in one or more of the vehicle's tires, up to a total of four tires, is equal to or less than either the pressure 25 percent below the vehicle manufacturer's recommended cold inflation pressure, or the pressure specified in the 3rd column of Table 1 of this standard for the corresponding type of tire, whichever is higher; [...]

S4.3 Low tire pressure warning telltale. S4.3.1 Each tire pressure monitoring system must include a low tire pressure warning telltale that: (a) Is mounted inside the occupant compartment in front of and in clear view of the driver; (b) Is identified by one of the symbols shown for the “Low Tire Pressure” Telltale in Table 1 of Standard No. 101 (49 CFR 571.101); and (c) Is illuminated under the conditions specified in S4.2. S4.3.2 In the case of a telltale that identifies which tire(s) is (are) under-inflated, each tire in the symbol for that telltale must illuminate when the tire it represents is under-inflated to the extent specified in S4.2. [...]

S4.4 TPMS malfunction. (a) The vehicle shall be equipped with a tire pressure monitoring system that includes a telltale that provides a warning to the driver not more than 20 minutes after the occurrence of a malfunction that affects the generation or transmission of control or response signals in the vehicle's tire pressure monitoring system. The vehicle's TPMS malfunction indicator shall meet the requirements of either S4.4(b) or S4.4(c). (b) Dedicated TPMS malfunction telltale. The vehicle meets the requirements of S4.4(a) when equipped with a dedicated TPMS malfunction telltale that: (1) Is mounted inside the occupant compartment in front of and in clear view of the driver; [...]

S4.5 Written instructions. (a) Beginning on September 1, 2006, the owner's manual in each vehicle certified as complying with S4 must provide an image of the Low Tire Pressure Telltale symbol (and an image of the TPMS Malfunction Telltale warning (“TPMS”), if a dedicated telltale is utilized for this function) with the following statement in English: Each tire, including the spare (if provided), should be checked monthly when cold and inflated to the inflation pressure recommended by the vehicle manufacturer on the vehicle placard or tire inflation pressure label. [...]

S5.1 Ambient temperature. The ambient temperature is between 0 °C (32 °F) and 40 °C (104 °F).

S5.2 Road test surface. Compliance testing is conducted on any portion of the Southern Loop of the Treadwear Test Course defined in appendix A and Figure 2 of section 575.104 of this chapter. The road surface is dry during testing.

S5.3.1 Test weight. The vehicle may be tested at any weight between its lightly loaded vehicle weight and its gross vehicle weight rating (GVWR) without exceeding any of its gross axle weight ratings.

S5.3.2 Vehicle speed. The vehicle's TPMS is calibrated and tested at speeds between 50 km/h (31.1 mph) and 100 km/h (62.2 mph). For vehicles equipped with cruise control, cruise control is not to be engaged during testing.

S5.3.3 Rim position. The vehicle rims may be positioned at any wheel position, consistent with any related instructions or limitations in the vehicle owner's manual.

S5.3.4 Stationary location. The vehicle's tires are shaded from direct sun when the vehicle is parked.

S6 Test procedures. (a) Inflate the vehicle's tires to the cold tire inflation pressure(s) provided on the vehicle placard or the tire inflation pressure label. (b) With the vehicle stationary and the ignition locking system in the “Lock” or “Off” position, activate the ignition locking system to the “On” (“Run”) position or, where applicable, the appropriate position for the lamp check. The tire pressure monitoring system must perform a check of lamp function for the low tire pressure telltale as specified in paragraph S4.3.3 of this standard. If the vehicle is equipped with a separate TPMS malfunction telltale, the tire pressure monitoring system also must perform a check of lamp function as specified in paragraph S4.4(b)(4) of this standard. (c) If applicable, set or reset the tire pressure monitoring system in accordance with the instructions in the vehicle owner's manual. (d) System calibration/learning phase. (1) Drive the vehicle for up to 15 minutes of cumulative time (not necessarily continuously) along any portion of the test course. [...]

S7.1 Vehicles manufactured on or after October 5, 2005, and before September 1, 2006. For vehicles manufactured on or after October 5, 2005, and before September 1, 2006, the number of vehicles complying with this standard (except for the provisions of S4.4 unless the manufacturer elects to also certify to those provisions) must not be less than 20 percent of: (a) The manufacturer's average annual production of vehicles manufactured on or after September 1, 2002, and before October 5, 2005; or (b) The manufacturer's production on or after October 5, 2005, and before September 1, 2006.

S7.2 Vehicles manufactured on or after September 1, 2006, and before September 1, 2007. For vehicles manufactured on or after September 1, 2006, and before September 1, 2007, the number of vehicles complying with this standard (except for the provisions of S4.4 unless the manufacturer elects to also certify to those provisions) must not be less than 70 percent of: (a) The manufacturer's average annual production of vehicles manufactured on or after September 1, 2003, and before September 1, 2006; or (b) The manufacturer's production on or after September 1, 2006, and before September 1, 2007.

S7.3 Vehicles manufactured on or after September 1, 2007. Except as provided in S7.7, all vehicles manufactured on or after September 1, 2007 must comply with all requirements of this standard.

S7.4 Calculation of complying vehicles. (a) Carry-Forward Credits. For purposes of complying with S7.1, a manufacturer may count a vehicle if it is certified as complying with this standard and is manufactured on or after April 8, 2005, but before September 1, 2006. (b) For purposes of complying with S7.2, a manufacturer may count a vehicle if it: (1) (i) Is certified as complying with this standard and is manufactured on or after April 8, 2005, but before September 1, 2007; and (ii) Is not counted toward compliance with S7.1; or (2) Is manufactured on or after September 1, 2006, but before September 1, 2007. (c) Carry-Backward Credits. [...]

S7.5 Vehicles produced by more than one manufacturer. S7.5.1 For the purpose of calculating average annual production of vehicles for each manufacturer and the number of vehicles manufactured by each manufacturer under S7.1 through S7.3, a vehicle produced by more than one manufacturer must be attributed to a single manufacturer as follows, subject to S7.5.2: (a) A vehicle that is imported must be attributed to the importer. (b) A vehicle manufactured in the United States by more than one manufacturer, one of which also markets the vehicle, must be attributed to the manufacturer that markets the vehicle. [...]

S7.6 Small volume manufacturers. Vehicles manufactured by a manufacturer that produces fewer than 5,000 vehicles for sale in the United States during the period of September 1, 2005 to August 31, 2006, or the period from September 1, 2006 to August 31, 2007, are not subject to the corresponding requirements of S7.1, S7.2, and S7.4.

Defined terms

The standard defines 2 terms in its definitions section; the first 2 are quoted here from the eCFR.

• Lightly loaded vehicle weight means unloaded vehicle weight plus the weight of a mass of 180 kg (396 pounds), including test driver and instrumentation.
• Tire pressure monitoring system means a system that detects when one or more of a vehicle's tires is significantly under-inflated and illuminates a low tire pressure warning telltale.

Limits of this page

This page quotes the text of 49 CFR 571.138 as published in the eCFR, current through October 29, 2026. It omits tables, figures, cross-referenced test procedures in other parts, and the preambles and rulemaking history that explain the rule. It does not tell you whether a given vehicle, part or product complies, how to run a test, or what a manufacturer must certify. Compliance questions go to the manufacturer's engineers, qualified counsel or NHTSA. The eCFR is an editorial compilation, not the official legal edition of the Federal Register.

Sources

Sources opened and read November 2, 2026.

• eCFR: 49 CFR 571.138, Standard No. 138; Tire pressure monitoring systems. (current through October 29, 2026) (read November 2, 2026)
• eCFR: 49 CFR part 571, Federal Motor Vehicle Safety Standards (current through October 29, 2026) (read November 2, 2026)