9.1 Exhaust System, Noise Evidence & Visible Emissions

Exhaust integrity and noise

An internal-combustion vehicle must have an exhaust system including effective sound reduction. Inspect the complete visible route from engine connection to outlet. Reject insecurity, a fume leak, a system readily adjustable to defeat effectiveness, or heat/fume routing that can harm occupants or damage fuel, brake, electrical, or body components. The tailpipe and body openings matter because fumes must not accumulate in the passenger compartment.

Externally venting wastegates (“screamer pipes”) are not permitted because they are not adequately muffled and do not discharge behind the passenger compartment. A wastegate routed back into the exhaust or through its own compliant muffled rear-discharge system is different.

Noise decisions and evidence

Compare output with the original system or a similar vehicle. Where increased noise is not clearly acceptable, follow the page and Technical Bulletin 1 quick-check route. Table 11-1-1 contains class/date-specific quick-check figures; there is no single “typically 90 dBA” limit for every light vehicle.

Valid objective evidence can include the specified certificate and tailpipe label or the current electronic data plate. From September 2025, green or orange electronic labels can carry objective-noise information; verify the electronic record and that it covers the present system.

A vehicle presented because it was pink- or green-stickered for exhaust noise must have a valid objective test completed after that order. Even an earlier noise certificate or a later quieter-looking exhaust does not remove that requirement.

Visible smoke test

Bring the engine to normal operating temperature. Reject clearly visible smoke from the tailpipe for a continuous five seconds:

• while idling, where the vehicle does not meet a table exception; or
• during the specified acceleration test, subject to the VIRM procedure and exceptions.

If the vehicle initially fails, the page directs the inspector to ensure normal temperature, purge at about 2500 rpm (or half maximum engine speed if lower) for about five seconds, then repeat the idle and acceleration tests. Water-vapour condensation is not smoke. The table provides routes for particular original engine designs and recognises moderate diesel turbo-lag smoke in the stated situation.

For relevant non-group-L vehicles first registered in New Zealand from 1 May 2010 and manufactured from 1 January 1990, removal of an originally fitted catalytic converter or diesel particulate filter is rejected without the prescribed entry-certifier metered-emissions evidence. The summary legislation refers to first certification from 1 May 2008; read the exact reason and notes for the presented facts.

Inspection sequence

1. Inspect mounting, joints, mufflers, outlet, clearance, shields, and fume paths.
2. Identify valves, bypasses, or readily adjustable noise devices.
3. Compare noise and use the approved quick-check/evidence route.
4. Check any enforcement order date against objective-test evidence.
5. Warm the engine and perform the specified five-second smoke observations.
6. Distinguish smoke from condensation and apply documented exceptions.
7. Check evidence of removed emissions-control equipment where the date criteria apply.

Scenario

A modified exhaust has a valid objective-noise certificate from June. The vehicle was ordered off the road for noise in August. The June evidence is insufficient; a new objective test after the August order is required.

Evidence scope and test preparation

Match an objective-noise certificate, label or electronic record to the vehicle and exhaust configuration. A certificate for an earlier tailpipe/muffler arrangement does not necessarily cover later changes. The quick check is a screening process under its bulletin, while an objective test is performed by the authorised specialist; do not improvise a phone-meter substitute.

Before judging smoke, distinguish oil smoke, over-fuelling smoke and coolant-like vapour only to support diagnosis—the certification criterion remains visible smoke under the prescribed conditions. Stop a test if engine condition makes continued acceleration unsafe. The purge/retest route is not an endless series of attempts; once the valid repeated test still meets the rejection condition, record the fail.

Heat, fumes and outlet detail

Inspect shields and clearance wherever exhaust heat could affect the passenger floor, fuel system, brake lines, wiring or combustible material. The VIRM uses a harm/effectiveness criterion rather than a universal 15 mm clearance, so assess actual design, shielding and damage. Confirm the outlet position does not allow fumes to enter through doors, windows or body openings.

A small soot mark may help locate a leak but is not itself the complete decision; safely establish whether fumes escape. Flexible joints, turbo connections and repaired seams deserve attention under operating conditions without exposing the inspector to hot or moving parts.