Snap-On Diagnostics DGA 1000, Manual, Page: 51 / 116

Vehicle Testing
3-3
Testing Tips
X
Read and follow the safety instructions in Safety Information in
this manual.
X
Always comply with the governing emission control standards
and regulations in your locality when testing exhaust emission
levels.
X
Check vehicle manufacturer specifications and procedures
before testing.
X
Do not test exhaust emissions on vehicles that are smoking
excessively or are in obvious need of engine repair. Testing
exhaust gas under such conditions may contaminate the
sampling system and cause inaccurate readings.
X
Always follow vehicle manufacturer specifications when working
on emission control devices to comply with anti-tampering laws.
X
Test engines only when they are at normal operating
temperature.
— Testing a cold engine does not provide useful test results
due to fuel mixture enrichment.
— A cold engine test contaminates the sampling filter quickly,
requiring more frequent analyzer service intervals.
X
Before testing tail pipe emission levels, make sure the engine is
at normal operating temperature.
X
Repair leaks in the exhaust system prior to testing. Leaks
adversely affect analyzer readings.
X
Disable Air Injection Reaction (AIR) systems before performing
some diagnostic tests. This provides undiluted gas samples and
inhibits catalytic converter operation. Check the procedure
prescribed by the manufacturer for disabling the AIR system.
X
Insert the sample probe fully into the tail pipe when testing
exhaust emissions to prevent diluted readings.
X
Exhaust samples can be diluted by outside air entering twin tail
pipes connected to a common resonator or muffler. Block off the
pipe not being used for the sample probe when testing these
exhaust systems.
— Remove the device blocking the tail pipe when testing is
complete.
— Do not block a tail pipe when operating a vehicle on a
chassis dynamometer.