Buick Regal Exhaust and Emissions Service Guide (2018-2020)

The exhaust and emissions system on the 2018-2020 Regal is not complicated, but it is easy to spend money in the wrong place on it. This is the version we give people at the counter.

What You Will Notice First

A diesel that regenerates far more often than it used to
An exhaust tick on cold start that quiets as the manifold expands
A P0420 or P0430 efficiency code
A check engine light that appears after fueling and clears itself

None of these are emergencies on day one. All of them get more expensive if you sit on them.

The Parts Involved

Catalytic converters.
Oxygen sensors.
DEF injectors.
Diesel particulate filters.
EVAP purge valves.
Exhaust manifolds.

Why the Factory Part Matters Here

Catalytic converters are emissions-certified parts, and substrate loading is what the downstream oxygen sensor is judging.
EVAP components are leak-rate sensitive, and the monitor is comparing against a factory reference.
Diesel aftertreatment parts are tightly integrated with the calibration.

Service Interval

Not scheduled. Converters are warranted separately under federal emissions rules, so check coverage before you buy.

Ordering Notes

Emissions equipment varies by state of original sale on some model years. On the Regal specifically, trim and package content is the thing that trips people up.

Genuine GM parts, dealer priced, shipped from Dallas. our Buick OEM parts catalog has the full catalog, or search for catalytic converters.