Wash. Rev. Code » Title 46 · Chapter 46.37
Revised Code of Washington

Wash. Rev. Code § 46.37.390 (2026)

✓ current as of May 2026
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(1) Every motor vehicle shall at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise, and no person shall use a muffler cut-out, bypass, or similar device upon a motor vehicle on a highway.
(2)(a) No motor vehicle first sold and registered as a new motor vehicle on or after January 1, 1971, shall discharge into the atmosphere at elevations of less than three thousand feet any air contaminant for a period of more than ten seconds which is:
(i) As dark as or darker than the shade designated as No. 1 on the Ringelmann chart, as published by the United States bureau of mines; or
(ii) Of such opacity as to obscure an observer's view to a degree equal to or greater than does smoke described in subsection (a)(i) above.
(b) No motor vehicle first sold and registered prior to January 1, 1971, shall discharge into the atmosphere at elevations of less than three thousand feet any air contaminant for a period of more than ten seconds which is:
(i) As dark as or darker than the shade designated as No. 2 on the Ringelmann chart, as published by the United States bureau of mines; or
(ii) Of such opacity as to obscure an observer's view to a degree equal to or greater than does smoke described in subsection (b)(i) above.
(c) For the purposes of this subsection the following definitions shall apply:
(i) "Opacity" means the degree to which an emission reduces the transmission of light and obscures the view of an object in the background;
(ii) "Ringelmann chart" means the Ringelmann smoke chart with instructions for use as published by the United States bureau of mines in May 1967 and as thereafter amended, information circular 7718.
(3) No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase the noise emitted by the engine of such vehicle above that emitted by the muffler originally installed on the vehicle, and it shall be unlawful for any person to operate a motor vehicle not equipped as required by this subsection, or which has been amplified as prohibited by this subsection. A court may dismiss an infraction notice for a violation of this subsection if there is reasonable grounds to believe that the vehicle was not operated in violation of this subsection.
This subsection (3) does not apply to vehicles twenty-five or more years old or to passenger vehicles being operated off the highways in an organized racing or competitive event conducted by a recognized sanctioning body.
[ 2006 c 306 s 4; 2001 c 293 s 1; 1977 ex.s. c 355 s 33; 1972 ex.s. c 135 s 1; 1967 c 232 s 3; 1961 c 12 s 46.37.390. Prior: 1955 c 269 s 39; prior: 1937 c 189 s 36; RRS s 6360-36; RCW 46.36.050; 1927 c 309 s 17; 1921 c 96 s 21; 1915 c 142 s 20; RRS s 6362-17.]

Notes:

Rules of court: Monetary penalty schedule—IRLJ 6.2.
Severability—1977 ex.s. c 355: See note following RCW 46.37.010.
Motorcycles and motor-driven cycles—Additional requirements and limitations: RCW 46.37.539.
Notes of Decisions
Cited in 12 cases (1 in the last 5 years), 1994–2024 · leading case: State v. Arreola, 290 P.3d 983 (Wash. 2012).
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State v. Arreola, 290 P.3d 983 (Wash. 2012). · cites it 3× “¶5 The trial court found that Officer Valdivia’s “primary motivation in pulling the car over was to investigate the reported DUI,” but this “was not the sole reason for the stop.”
State v. Cole, 871 P.2d 656 (Wash. Ct. App. 1994). “RCW 46.37.390; RCW 46.61.140. *846 Trooper Lee Slemp and Deputy Vincent Waltz, in another car, followed Sergeant Boling to assist.”
State v. Arreola, 260 P.3d 985 (Wash. Ct. App. 2011). · cites it 4× “Chacon was under the influence of alcohol but could hear that the car was equipped with an after-market exhaust system, amplifying the noise of the engine in violation of RCW 46.37.390(3). [2] He followed the Chevy southbound for roughly a half mile, at which point Mr.”
State v. Pettit, 251 P.3d 896 (Wash. Ct. App. 2011). “Pettit because his car had a loud exhaust, generated by a "coffee can" muffler, which RCW 46.37.390(1) and (3) prohibit. Verbatim Report of Proceedings (VRP) at 9.”
State v. Pettit, 251 P.3d 896 (Wash. Ct. App. 2011). “Pettit because his car had a loud exhaust, generated by a “coffee can” muffler, which RCW 46.37.390(1) and (3) prohibit. Verbatim Report of Proceedings at 9.”
State v. Olsson, 895 P.2d 867 (Wash. Ct. App. 1995). · cites it 5× “He argues RCW 46.37.390, which requires motor vehicles to be equipped with a muffler which is sufficient "to prevent excessive or unusual noise”, is unconstitutionally vague.”
State Of Washington v. Matthew C. Caldwell (Wash. Ct. App. 2020). · cites it 2× “2 Under RCW 46.37.390(1), “Every motor vehicle shall at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise.”
State Of Washington, V Michael T. Waye (Wash. Ct. App. 2024). · cites it 2× “58292-9-II an altered exhaust in violation of RCW 46.37.390. Id. at 288-89 . The officer then pulled over the vehicle, still without seeing any signs of intoxicated driving.”
State of Washington v. Brent Douglas Reedy (Wash. Ct. App. 2016). “RCW 46.37.390(3). It is a sufficient basis for a stop.”
State Of Washington v. William Kelly Piland (Wash. Ct. App. 2020). “The officer did not observe any signs of intoxication but noticed that the vehicle had an altered exhaust and stopped Chacon Arreola for violating RCW 46.37.390. Id. at 289 . The officer testified at the suppression hearing that the muffler violation was an actual reason for the…”
State Of Washington, Resp. v. Christopher M. Smith, Sr., App. (Wash. Ct. App. 2013). “"47 In Arreola, Officer Valdivia's primary motivation in pulling the defendant's car over was to investigate a reported DUI.”
State of Washington v. Guadalupe Arousa, Jr. (Wash. Ct. App. 2015). “But, because his secondary motivation, the car's altered exhaust in violation of RCW 46.37.390, was an actual reason to stop the defendant, the stop was not pretextual.”
— Wash. Rev. Code § 46.37.390(1) — 5 cases
State v. Arreola, 290 P.3d 983 (Wash. 2012). “¶5 The trial court found that Officer Valdivia’s “primary motivation in pulling the car over was to investigate the reported DUI,” but this “was not the sole reason for the stop.”
State v. Pettit, 251 P.3d 896 (Wash. Ct. App. 2011). “Pettit because his car had a loud exhaust, generated by a "coffee can" muffler, which RCW 46.37.390(1) and (3) prohibit. Verbatim Report of Proceedings (VRP) at 9.”
State v. Pettit, 251 P.3d 896 (Wash. Ct. App. 2011). “Pettit because his car had a loud exhaust, generated by a “coffee can” muffler, which RCW 46.37.390(1) and (3) prohibit. Verbatim Report of Proceedings at 9.”
State v. Olsson, 895 P.2d 867 (Wash. Ct. App. 1995). “He argues RCW 46.37.390, which requires motor vehicles to be equipped with a muffler which is sufficient "to prevent excessive or unusual noise”, is unconstitutionally vague.”
State Of Washington v. Matthew C. Caldwell (Wash. Ct. App. 2020). “2 Under RCW 46.37.390(1), “Every motor vehicle shall at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise.”
— Wash. Rev. Code § 46.37.390(3) — 2 cases
State v. Arreola, 260 P.3d 985 (Wash. Ct. App. 2011). “Chacon was under the influence of alcohol but could hear that the car was equipped with an after-market exhaust system, amplifying the noise of the engine in violation of RCW 46.37.390(3). [2] He followed the Chevy southbound for roughly a half mile, at which point Mr.”
State of Washington v. Brent Douglas Reedy (Wash. Ct. App. 2016). “RCW 46.37.390(3). It is a sufficient basis for a stop.”
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