From:
http://www.emissiontestwa.com/faq.aspx
#
1982 and newer diesel vehicles under 8501 pounds Gross Vehicle Weight (GVW) with two-wheel or part-time four wheel drive.
These vehicles will receive an opacity test that measures the density (opacity) of exhaust as it exits the vehicle's tailpipe. The vehicle is tested on a dynamometer. All front wheel drive vehicles will be operated by Inspection personnel. Motorists may operate rear wheel drive vehicles on the dynamometer.
#
1982 and newer diesel vehicles under 8501 pounds Gross Vehicle Weight (GVW) with constant 4x4 (all wheel drive) or traction control.
These vehicles will receive an opacity test that measures the density (opacity) of exhaust as it exits the vehicle's tailpipe. The vehicle will not be driven on a dynamometer. The motorist will be instructed to reach required RPM levels while the vehicle idles in park or neutral (depending on the transmission or model-year type of vehicle).
#
1982 and newer diesel vehicles over 8500 pounds Gross Vehicle Weight (GVW). These vehicles will receive a snap acceleration test.
The vehicle exhaust's density (opacity) will be measured as it exits the vehicle's tailpipe. The vehicle will not be driven on a dynamometer. The motorist will be instructed to reach required RPM levels while the vehicle idles in park or neutral (depending on the transmission or model-year type of vehicle).tested.
---snip---
How do I receive a waiver?
Any emission test facility can provide you with a waiver, if your vehicle fails the initial test, is repaired by an Authorized Emission Specialist and fails its second test. All emission components must be present, connected and operating properly. You must provide proof that at least the minimum amount required for the waiver was spent for proper diagnosis and emission-related repairs. Refer to the brochure provided to you when your vehicle first failed for waiver requirement information.