MSPC Advisory Circular 

ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF AIR PROGRAMS MOBILE SOURCE POLLUTION CONTROL PROGRAM 

A/C No. 24 December 11, 1972 Page 1 of 4 pages 

Subject: Prohibition of USC of Emission Control Defeat Devices 

A. Purpose 

The purpose of this Advisory Circular la to notify 

manufacturers that EPA will refuse to certify vehicles equipped with 

emission control defeat devices and to inform manufacturers as to the 

authority and criteria for any such refusal by EPA. The Circular also 

applies the policy set forth to the approval of running changer and field 

fixes involving the addition of Defeat Devices to vehicles. 

B. Background 

1. In a letter of July 12, 1972, the Administrator notified 

all manufacturers of light duty motor vehicles that the Agency considers 

sensors and devices which may adversely affect emission control under 

conditions or during operations likely to occur in actual vehicle use 

to be inconsistent with the intent of the Clean Air Act. Specifically, 

it is the intent of the Act that vehicles be designed, built, and equipped 

so that when they are being-used by the motoring public emissions will be 

reduced to the extent indicated by the prescribed standards during the 

period of their useful life. The fact that it may not be practicable to 

test prototype or production vehicles in order to assure the reductions 

under many conditions which the vehicle will encounter does not mean 

intentional obviation of these reductions outside the parameters of the 

test procedure is consistent with the Act. 

2. The “intent of the Clean Air Act” referred co in the letter 

has in part been implemented by regulations as regards test vehicles. 

Paragraph 85.073-9(d) requires that all emission control systems 

“shall be functioning” during the Federal Test Procedure. Paragraphs 

85.073-7(a) and (b) provide that emission data vehicles and durability 

data vehicles, respectively, “shall be driven... with all emissions 

control systems installed and operating...” during all mileage 

accumulation. These provisions are in the regulations to insure that 

emissions control systems and devices which operate to achieve emissions 

reductions during emission tests operate similarly during mileage accumulation so that their ability to achieve similar emission reductions during 

normal use for five years or 50,000 miles may be reasonably assessed. 
ENVIRONMENTAL PROTECTION AGENCY OFFICE OF ALL PROGRAMS A/C NO. 24 PAGE 2 OF 4 

Devices which are designed to compromise the emission control effectiveness 

of any system during mileage accumulation as compared with effectiveness 

during emissions testing are inconsistent with the letter and purpose of 

the teat procedures. Hence, EPA cannot certify test vehicles employing 

such devices. 

C. Applicability 

The policy outlined in this Advisory Circular is effective and 

applicable immediately. The provisions of this Advisory Circular apply 

to certification testing beginning with the 1974 model year and to 

running changes and field fixes which would involve the addition of any 

Auxiliary Emission Control Device (AECD) on any model year vehicle. 

D. Definitions 

1. Auxiliary Emission Control Device (AECD). An AECD is any 

element of design which senses temperature, vehicle speed, engine RPM, 

transmission gear, manifold vacuum, or any other parameter for the purpose 

of activating, modulating, delaying, or deactivating the operation of any 

part of the emission control system. 

2. Defeat Device. A Defeat Device is an AECD that reduces the 

effectiveness of the emission control system under conditions which may 

reasonably be expected to be encountered in normal urban vehicle operation 

and use, unless (1) such conditions are substantially Included in the 

Federal emission test procedure, or (2) the need for the AECD is justified 

in terms of protecting the vehicle against damage or accident, or (3) the 

AECD does not go beyond the requirements of engine starting. 

E. Criteria for Determining the Acceptability of Certain AECDs 

1. An AECD is generally deemed to be a Defeat Device if it is 

determined by EPA to reduce the effectiveness of an emission control system: 

a. In response to any ambient, underhood or passenger 

compartment air temperature outside the 68°- 86° F range; 

b. In response to any accessory operating condition not 

encountered during the Federal emission teat;. 

C. After any time span in a specific vehicle operating mode. 

2. AECDs that generally are acceptable Include those which 

reduce the effectiveness of an emission control system in response to: 

a. Engine temperatures (as sensed by oil or coolant 

temperature or some other direct indicator) which are outside the range 

of normal, stabilized operating temperatures; 

b. Unusual engine, emission control system, or 

vehicle operating conditions which may reasonably be expected to cause 

damage or destruction to the engine or vehicle; 
C. Dmuuel engino, rrirrloa control system, or vehicle 

operating cdltloas vhich my ree8onably be crpected to present a ufety 

problem; 

d. The engagement of the trensmlsrion wr, es loug es 

no the delay Is mloyed. 

P. Determlnatiaa of Accepteblllty of Specific Devices 

1. All AlKDr mst be described In the msnufacturer’s application 

for certlflcetioa. Bared upon the description of the devlca, date 

derived from such testing es EPA pup require or conduct, end any rhowlngs 

made by the asnufacturer, EPA will determine whether the device Is 

acceptable or whether It Is a Defeat Device. 

2. The cetegorler In Section E. above, are lllurtretlve only. 

Therefore, the l cceptebfllty of each device vi11 be deterpined on en 

individual basis since some dcvlccr mry not flt Into one of the catsgorier 

In Section g. above, others are difficult to categorize, and still other8 

say have more then one purpose. If the device Is deterolned to be a 

Defut Device, EPA will advise the msnufecturer in writing that test 

vehicles Incorporating such a device arc not eligible to provide date on 

the basis of which certification mry be lamed. 

3. he policy stated hereln will also be aTplIed with rerpect to 

determinations by EPA under 40 CFR 85.073-33 and 3:. (running changer), and 

approvals under 40 CF’R 8S.073.S(f) (carry-over datlj. 

4. Any 1974 model year vehicle which ha8 :rgun mileage eccumuletlon with a Defeat Device Installed and operating is disallowed, unless the 

manufacturer cm show that such operation cannot reasonably be concluded 

to have an impact on the deterioration of the emission control system. 

c. Use of Carry-over Data 

If, in accordance with Advisory Circular No. 17, a menufecturcr 

has propored the uoe of carry-over data for 1974, such date will be 

accepted to the extent that the date did not originate from vehicle8 

equipped with Defeat Devlcer. If Defeat Devlcea were used on 1973 

model yur durability vehicles to generate date intended to be used 

l s the beoir for 1974 model year cettlflcetlon, testing of 1974 model 

yur durability vehicles which do not contain such devlcee ory be required, depending upon E2A’s judgment whether the use of the device ouy 

r+asonably be expected to have affected det.qK$oratios.of thc.1973 vehicle. 
I’. %,I” ( : ,.’ : :.’ : , ;; L_ r, .!‘b . ;rl’ ::, { l ,I.. ;.4 I (,X, ,.f,“’ i,;a "I 1 26. i’,‘,; : 4 

----w - -. __ __ -- -..---- I_ --.- _---. ___- - ._-_ --- -___--_- - _ ----.-.. -. -.. _-_ 

If DefUt TkPfCU Were Ured on 1973 Podel yur MiSSiOn dew vehicle8 

to generate date intended to be used es the beslr for 1974 model year 

certlflcation, testing of 1974 model year eml88lon date vehicles which 

do not coat&in such devices vlll be required, 

kloblle Source Pollution Control 

Program