This inspection applies to all spark ignition engined vehicles
with four or more wheels in Classes IV and VII.
Contained within this section are flowcharts. Carefully use these
flowcharts to accurately establish which type of emission test is
applicable to the vehicle being tested-
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Test according to which is older, engine or vehicle.
e.g. A 1995 car fitted with a 1991 engine (of whatever make), test
to 1991 standards for emission purposes.
Note: The onus is on the vehicle presenter
to prove engine age.
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(
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Vehicles fitted with modified engines
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If an engine has been modified in any way, it still has to meet
the exhaust emission requirements according to the age of the vehicle.
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Personal Imports
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The following notes should be used in conjunction
with the flowcharts on the following pages.
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(3) Advice on establishing whether the design
gross weight of a large car exceeds 2500kg
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The vehicle will be tested according to its age from first use-The
only exemption to this is if the vehicle owner can present to the
tester at time of test a letter from the vehicle manufacturer stating
that the particular engine as originally installed could not meet
the equivalent British emission standards. If this is the case,
then test to the next lower emission standard.
e.g. A 1995 car first used in Africa has a letter from the engine
manufacturer stating that the particular engine (engine number to
be stated) cannot meet Catalyst emission limits, then use the pre
cat limits of CO 3.5%, HC )200ppm.
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(1) Two stroke engines do not require an emissions test unless
they are subject to the catalyst test-
(2) <= less than or equal to
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(3)
i) it may be shown on the
manufacturers VIN plate (example shown in Section 3.9, page 29)
ii) it may be listed only in Section 2 of the current emissions
data book
iii) refer to any readily available data, e.g. handbook or data
book
iv) if still unsure, assume it to be over 2500kg dgw.
4) Vehicles, which have been the subject of specialist conversions,
are to be treated, for emissions purposes, as if they had not been
converted, e.g. a motor caravan or ambulance converted from a goods
vehicle is still to be treated as not being a "passenger car",
an ambulance converted from a "passenger car" or a "passenger
car" with seats added is still to be treated as being a "passenger
car".
A vehicle originally built with 6 or more seats, in addition to
the driver, which has had seats removed is still to be treated as
not being a "passenger car"
(5) The full title of the Department of Transport Emissions book
is "In-Service Exhaust Emission Standards for Road Vehicles".
The latest edition must be used-
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Information
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Method of Inspection
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Reason for rejection
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Engine speed and temperature
When checking exhaust emissions, the engine must be at its normal
idle speed and normal operating temperature.
Engine speeds and temperature can be assessed either subjectively
or by reference to manufacturer's or other reliable data
Gas analyser probe
It-is important to ensure that the gas analyser probe is inserted
as fully as possible into the exhaust pipe and is secure.
Recording Emissions Test Results
Record the results of the test Via the VTS Device. (se introduction
paragraph 3 at the beginning of this inspection manual)
Early catalyst vehicles
The flowcharts and notes must be carefully followed. If a vehicle
is fitted with a catalyst it does not necessarily mean a 'CAT' test
is
required.
Early catalyst vehicles
The flowcharts and notes must be carefully followed. If a vehicle
is fitted with a catalyst it does not necessarily mean a 'CAT' test
is
required.
Working environment
To prevent the build up of fumes, the test should be carried out
in a well ventilated area.
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A. All vehicles
1. Raise the engine speed to around 2500 rpm or half the maximum
engine speed if this is lower.
Hold this speed steady for 20 seconds to ensure that the inlet and
exhaust system is properly purged. Allow the engine to return to
idle and the emissions to stabilise.
a. assess the engine idle speed.
b. assess the smoke emitted from the tailpipe at idle,
c. rapidly increase the engine speed to around 2500rpm or half maximum
. engine speed if this is lower and assess the smoke emitted from
the tailpipe. Allow the engine to return to idle.
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A. All vehicles
1. The engine
a. is idling at a speed clearly above its normal idling speed
b. emits dense blue or clearly visible black smoke for a continuous
period of 5 seconds at idle
c. emits excessive dense blue or clearly visible black smoke during
acceleration which would obscure the view of other road users.
Note: Older vehicles, particularly pre-1960. may emit unavoidable
smoke due to their design. Such smoke is not a reason for rejection.
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A. Non-catalyst test
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1. The Exhaust Emission Test
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2. Conducting the test
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3. Electric engine cooling fans
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A check of vehicle exhaust emissions is part of the MOT test for
all 4-stroke spark ignition engined vehicles with 4 or more wheels
in Class IV and VII.
Two of the exhaust gases are included
. Carbon Monoxide (CO)
. Hydrocarbons (HC)
Assessment on most vehicles is straightforward, but a number of
factors should be borne in mind.
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The test should be conducted with the engine warm. Testing a cold
engine could lead to an unjustified failure.
It is important to ensure that any enrichment device is not operating.
The engine should be idling normally during the test and should
not be subject to significant electrical loading such as heated
seats or heated rear windows.
If an engine will not idle, an assistant may apply light throttle
pedal pressure.
To assess that these conditions are met, MOT Testers can either
. Use their own judgement, or
. Refer to manufacturer's or other reliable data
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Many modern vehicles are fitted with electric engine cooling fans
which can cut in during an emission test. The extra load on
the alternator reduces the idle speed which causes the engine management
system to react. This gives rise to highly variable readings.
If this happens during a test, wait until the fan switches off
and the readings stabilise before continuing.
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4. Unstable readings
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5. Holed exhaust
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6. Total gas emitted
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Some vehicles give unstable readings due, for example to their
carburettor or fuel injection system design. Before failing
a vehicle, it is important to establish that a particular limit
has been exceeded constantly for a period of 5 seconds.
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A holed exhaust can allow air to be sucked in, causing artificially
low readings.
Where a vehicle has an exhaust holed to the extent that MOT failure
is warranted, the emissions should be rechecked when the exhaust
is repaired even if the vehicle does not leave the testing station
in the meantime. Owners should be made aware that any emission
readings taken with a leaking exhaust might be incorrect.
Holes not justifying MOT failures do not normally have a significant
effect on the exhaust gases at the tailpipe and can be ignored.
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The MOT limits prescribed relate to the total exhaust gas being
emitted by the vehicle.
If a vehicle has a dual exhaust system, then the emissions from
the tailpipes should be averaged. This is done by adding together
the readings and dividing by two, eg
1st pipe emits 6% CO, 400 ppm HC
2nd pipe emits 4% CO, 500 ppm HC
Average CO reading is
6+4/2=5%
Average HC reading is
400+500/2=450ppm
The Results of this type of test must be entered manually onto
the VTS Device.
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Single exhaust systems
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Dual exhaust systems
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7. Multi fuel vehicles
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A single exhaust system has at least one point in the system where
all the exhaust gases from the engine travel through the same pipe,
even though the system may split at some point to separate silencers
or tailpipes. Only one of these need be checked.
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A dual exhaust system has two separate pipes from the engine manifold
all the way back to the tailpipes. An exhaust system with
a balance tube between separate pipes is till considered a dual
exhaust.
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Vehicles which run on more than fuel (eg petrol and LPG) should
be tested on the fuel they are running on when presented.
There is a slight difficulty with LPG vehicles: the hydrocarbons
are propane rather than hexane. So the HC reading obtained must
be divided by the propane/hexane equivalency factor (PEF) marked
on the gas analyser. For example:
An LPG vehicle gives a HC reading of 700 ppm.
The PEF marked on the machine is 0.48.
So the actual MOT value is
700/0.48 = 1458 ie fail.
Some exhaust gas analysers have an automatic facility for doing
this.
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8. Vehicles which only just pass
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9. Vehicles which are incapable of passing
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Many modern vehicles will normally run well below the MOT limits.
Where such a vehicle just passes the MOT test, but the tester knows
that it is capable of more efficient operation, the owner should
be informed. Vehicles should normally be tuned to the manufacturer's
recommended settings wherever possible, but tuning is not part of
the MOT test.
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Regulations do not require vehicles to achieve CO or HC readings
below the original capability of the engine when new. A very
few vehicles may never have been able to meet the MOT limits.
Where a vehicle owner claims that this is the case, and has sound
supporting evidence (eg a letter from the vehicle manufacturer)'
the vehicle shuld be considered exempt from the CO and HC emission
requirements.
If the owner does not have sound supporting evidence, a Test Certificate
should be refused.
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B. Catalyst test
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1. The exhaust emission test
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2. Electric cooling fans and other accessories
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3.Total gas emitted
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The catalyst test is part of the MOT test for most class IV spark
ignition petrol engined passenger cars with four or more wheels
first used on and after 1 August 1992.
Carbon monoxide (CO), hydrocarbons (HC) and lambda (~) are
checked at fast idle speed and carbon monoxide (CO) is checked again
at idle speed.
The test should be self explanatory using the automated routine
on 1996 specification exhaust gas analysers The following
points should be borne in mind.
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If, during the catalyst emission test, the engine cooling fan
cuts in or out, this is not a problem and the test should continue
as normal. All other vehicle accessories (eg headlamps, air
conditioning, heaters) shall be turned off during the test.
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This paragraph should be read in conjunction with paragraph 6
non-catalyst test.
If a vehicle, which is subject to the catalyst emission test,
has a dual exhaust system, the test should be performed on both
tail pipes and the results averaged. This is done by adding
together the results and dividing by two, eg
Fast idle test
1st pipe:
0.4% CO, 25ppm HC, ~ = 1.01
2nd pipe:
0.2% CO, 15ppm HC, ~ = 1.03
Average CO: 0.4+0.2 / 2 =0.3%
Average HC: 25+15 / 2 =20ppm
Average ~: 1.01+1.03 /2 =1.02
Idle Test
1st pipe: 0.45% CO
2nd pipe: 0.35% CO
Average CO: 0.45+0.3 /2 =0.4%
The Results of this type of test must be entered manually onto
the VTS Device.
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4. Holed exhaust
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Refer to paragraph A5 non-catalyst test
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Exhaust Emissions - Spark Ignition - non
CAT Test
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Information
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Method of Inspection
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Reason for rejection
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When to do the test
It Is recommended that the engine is tested as soon as possible
after driving on the road
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B. Vehicles first used on or after 1 August 1975
1. Check that the analyser probe can be inserted into the tailpipe.
2. Use a suitable exhaust gas analyser to
determine the proportions of carbon monoxide {CO) and hydrocarbons
(HC in the exhaust gas over a period of at least 5 seconds at idle.
Note: Any residual hydrocarbons (ie those indicated by the analyser
when it is sampling only clean airj should be deducted from the
HC reading obtained from the vehicle.
Note: If a vehicle meets the CO requirement at its normal idling
speed but fails the HC check, re-check the HC level at a high idle
speed of 2000rpm. If the HC reading is 1200 ppm or less, the vehicle
will meet both the CO and HC requirements.
. the CO requirement must be met with the engine running at its
normal (low) idling speed
. do not use a cold start/cold running mechanism to achieve a high
idle speed. Instead, apply light pressure to the throttle pedal.
. HC not applicable to Compressed Natural Gas (CNG) fuelled vehicles.
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B. Vehicles first used on or after 1 August 1975
1. The emissions cannot be measured because a tailpipe accessory
is fitted which prevents Insertion of the analyser
probe
2. The exhaust gas contains
a. a carbon monoxide content
exceeding the limit for a continuous period of 5 seconds
b. a hydrocarbon content exceeding the limit for a continuous period
of 5 seconds.
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Exhaust Emissions - Spark Ignition - BET
Test
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Information
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Method of Inspection
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Reason for rejection
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Printouts and check sheets
The 1996 specification analysers will produce two printouts. One
printout must be retained by the VTS for a period of three months,
the other printout must be given to the vehicle presenter.
Gas analyser probe
It is important to ensure that the gas analyser probe is inserted
as fully as possible into the exhaust pipe and is secure.
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1.
a. A suitable exhaust gas analyser will be needed to perform this
inspection-Check that the analyser probe can be inserted into the
tailpipe.
b. Ensure that the analysers daily leak check has been performed.
2. From 1 August 1992 onwards Basic Emission Test
(BET)
a. Carry out the test using the flowchart.
b. ensure that the engine is hot by checking for example - temperature
gauge, cooling fan cut-in or hot coolant hoses. If the engine is
not at normal temperature raise the engine speed to between 2000
and 3000rpm and maintain this speed until normal temperature has
been reached.
c. attach engine speed measuring device. It is permissible for the
purposes of this check to use the vehicle tachometer.
d. ensure the engine is idling normally.
e. perform a HC hang-up check and ensure that HC<20ppm before
continuing. Insert the analyser sample probe.
f. fast idle test: Raise the engine speed to a fast idle between
2500 and 3000rpm and hold steady. Note the readings for CO, HC and
lambda, and
record the results.
g. Idle test: Allow the engine to idle. Note the CO reading and
record the result.
h. remove analyser sample probe.
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1. The emissions cannot be measured because a tailpipe accessory
is fitted which prevents insertion of the analyser probe.
2. If the vehicle does not meet the BET limits go to CAT 1 button.
Note: There is no reason for rejection for vehicles that do not
meet the BET limits.
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Exhaust Emissions - Spark Ignition - CAT
Test
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Information
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Method of Inspection
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Reason for rejection
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When to do the test
It is recommended that the extended test is carried out as soon
as possible after the BET Test. This allows the test to be carried
out on a fully warmed up engine.
Printouts
The 1996 specification analysers will produce two printouts. One
printout must be retained by the VTS for a period of three months,
the other printout must be given to the vehicle presenter.
Cosmetic engine covers
Where engine speed can only be measured by the removal of a cosmetic
engine cover the engine speed must be measured if the cover can
be easily un-clipped. Otherwise, engine speed measurement may be
by-passed-
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1. A suitable exhaust gas analyser will be needed to perform this
inspection. Check that the analyser probe can be inserted into the
tailpipe.
2.
a. Ensure that the analyser's daily leak check has been performed.
b. identify the vehicle specific test limits using the flow charts.
c. connect the engine speed measuring device and insert the engine
oil temperature measuring probe into the dipstick hole
Note: Engine speed and engine oil temperature must be measured whenever
possible. If engine speed cannot be measured then the vehicle tachometer
should be used if fitted. Otherwise, a subjective estimate should
be made. If engine oil temperature cannot be measured, see note
in paragraph d below
d. engine pre-conditioning: Check the engine oil temperature. If
it is below the minimum vehicle specific requirement, raise the
engine speed to between 2000rpm and 3000rpm and maintain this speed
until the minimum engine oil temperature has been reached. Remove
temperature measuring probe and replace dipstick
Note: Where, in exceptional circumstances, the engine oil temperature
cannot be measure (eg in the case of a dry sump engine), check one
of the following:
temperature gauge showed warm engine, cooling fan had cut in or
coolant pipes were hot.
e. perform a HC hang-up check and ensure
that HC<20ppm before continuing. Insert the analyser sample probe
f. 1 st Fast Idle Test: Raise the engine speed to the vehicle specific
fast idle speed and maintain for 30 seconds. If the engine speed
drifts outside the fast idle speed range, begin the 30 second countdown
again. During the last 5 seconds note the readings for CO, HC and
lambda, and record the results
g. If the vehicle has passed the first fast Idle test, then go to
paragraph (j), otherwise go to paragraph (h)
h. additional engine pre-conditioning:
Run the engine between 2000-3000rpm for 3 minutes or until all the
emissions are within limits. If the engine speed goes outside the
fast idle range, then freeze the countdown until the engine speed
is within range once again
i. 2nd Fast Idle Test: Repeat the procedure as laid down in paragraph
(f), then go to paragraph (j)
j. catalyst stabilisation; Raise the engine speed to the vehicle
specific fast idle speed and maintain for 30 seconds. If the engine
speed drifts outside the fast idle speed range then begin the 30
second countdown again
k. idle test: Allow the engine to idle during a 30 second countdown.
During the last 5 seconds, note the CO reading and record the result
I. Remove analyser sample probe and engine speed measuring device.
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1. The emissions cannot be measured because a tailpipe accessory
is fitted which prevents insertion of the analyser probe.
2.
a. The engine idle speed is clearly above he vehicle specific limit.
Note: If the engine speed is clearly above the vehicle specific
limit and this can be easily adjusted, a tester may perform the
adjustment and complete the test - the adjustment is not, however,
part of the MOT test.
b. In the 2nd fast idle test, one or more of the following exceeds
the vehicle specific or default limits continuously for the last
5 seconds of the 30 second countdown"
. Carbon monoxide (CO)
. Hydrocarbons (HC)
. Lambda (l)
c. In the idle test. the following gas exceeds the vehicle specific
or default limit continuously for the last 5 seconds of the 30 second
countdown:
. Carbon monoxide (CO).
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Issue Date: 10th January 2005
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