3.3 Exhaust Emissions/Brakes

A Non-catalyst test
 
1.The Exhaust Emission Test 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 Classes IV and VII. Two of the exhaust gases are included Carbon Monoxide (GO) ·Hydrocarbons (HC) Assessment on most vehicles is straightforward, but a number of factors should be borne in mind.  
2. Conducting the Test 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  
B. Hydraulic systems (including Servo Assisted)
 
1. Fully depress the pedal twice, first slowly and then rapidly each time to a point where sustained pressure can be held.  Check for creep and sponginess. a. the pedal tends to creep down while the pedal is held under pressure
  b. sponginess indicating air in the hydraulic system
  2. If a vacuum servo is fitted, then with the engine off, totally deplete the stored vacuum by repeatedly applying the service brake.  Fully apply the brake and hold at a constant pressure.  Note whether the pedal can be felt to travel further when the engine is started. 2. No dip can be felt when the engine is started, indicating vacuum assistance is not working satisfactorily.
C. Full power hydraulic braking system
   
1. Check that a warning device is fitted. 1. No warning device fitted.
  2. Check whether a warning device fitted is audible or visible to driver.
  a. a warning device not visible (or audible) to the driver
  b. a visual warning device not readily visible to the driver in darkness
  3. With the engine switched off, repeatedly apply the service brake until the warning device operates.  Check that at least two further applications of the brakes are available.  In case of doubt the availability of two further applications can be established when testing the brakes on a Roller Brake Tester. Note: Hydraulic braking systems operate quietly.  It is normally necessary to use a roller brake tester to verify that the brakes are applied.
  a. a warning device not working correctly
  b. insufficient reserve pressure to give at least two further applications of the brakes after the warning device has operated
D. Air and vacuum systems (including ‘over hydraulic’

This inspection applies to vehicles registered on or after 1 October 1937

A vehicle of 3050kg or less unladen, with a reservoir coupled direct to the induction manifold, or a reservoir integral in a servo unit is not necessarily required to be fitted with a warning device

   
   
1. Check that a visual warning device or, as an alternative for vehicles first used on or after 1 April 1983, an audible warning device is  
a. fitted a. a mandatory warning device not fitted
b. working correctly b. a mandatory warning device not working correctly
Warning device

A defective audible warning device is not a reason for rejection if fitted in addition to an operational visual device.

For  vehicles first used on or after 1 April 1983, a defective visual warning device is not a reason for rejection if fitted in addition to an operational audible device.

2. Check that any visual warning device is 2. A visual warning device
a. visible from the driving seat a. not visible from the driver’s seat
b. illuminated, or otherwise visible from the driver’s seat in darkness b. not illuminated, or its function not visible from the driver’s seat in darkness
 

3. For systems fitted with a pressure or vacuum gauge, with the reservoir at a maximum pressure or vacuum, note the reading on the gauge and then fully depress the pedal.

Keep the pedal depressed and watch the gauge reading.

Note: All vehicles must also be checked for pressure or vacuum leaks during the under-vehicle inspection of the brake system.

3. The gauge reading drops whilst the pedal is kept depressed, indicating a leak in the brake system.
  4. Check that the operation of any air or vacuum-powered system (eg wipers etc) does not adversely affect the operation of the braking system 4. The repeated operation of any ancillary air or vacuum powered system completely depletes the stored air or vacuum for the braking system.
  5. By applying the service brake repeatedly, gradually empty the braking system, and
a. if a gauge is fitted, note that the reading on the gauge falls steadily each time the brake pedal is depressed, and when the gauge needle has reached the “warning mark”, there is still enough pressure or vacuum in the system to allow the brake to be applied at least twice more with pressure or vacuum assistance Note Pressure gauge
If pressure gauge has no warning mark, use 45 psi (3.1 kg/sq cm or 3 bar) as a reference.
Vacuum gauge
If the vacuum gauge has no warning mark, use 10” to 12” (25 to 30cm) as a reference.
a. Insufficient pressure or vacuum to give assistance to brakes for at least two or more applications after the gauge has reached the warning mark
b. If a warning light or other device is fitted, check that, after the warning has operated, there is still enough pressure or vacuum in the system to allow the brake to be applied at least twice more with pressure or vacuum assistance b. Insufficient pressure or vacuum to give assistance to brakes for at least two or more applications after the warning light or other device has operated
  6. Completely empty the reservoir by repeatedly pressing the service brake pedal.  Start the engine and if diesel run it at just below governed speed or 200 rpm if petrol.  Note the time it takes for the warning device to stop operating.2

6. The time between starting the engine and the warning device ceasing to operate,  the gauge showing a safe reading indicates that build-up of pressure/vacuum is low. For example more than 3 minutes for pressure systems

1 minute for vacuum system.

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