Exhaust, catalytic converter and DPF: what you need to know

What the exhaust system is made of#

The gases leave the engine through the exhaust manifold and pass through a series of parts to the tailpipe. In general you'll find:

• The catalytic converter: turns part of the harmful gases into less harmful ones.
• The particulate filter: a DPF on diesels, a GPF or OPF on some newer petrol cars. It traps soot from the gases and burns it off from time to time.
• Sensors (lambda, temperature, pressure), through which the engine computer watches the converter and the filter.
• The silencer: reduces the noise; it hangs under the car on brackets that can break.
• AdBlue, on many newer diesels: a fluid in a separate tank that reduces nitrogen oxides.

Signs of an exhaust problem#

• A louder exhaust, a rumble or a hiss: usually a hole, a crack or a blown gasket somewhere along the line.
• Rattling under the car, especially over bumps: a broken bracket, a loose heat shield or a pipe touching the body.
• A smell of fumes inside the car: a leak before the silencer. Open the windows and get the car to a garage as soon as you can: the gases contain carbon monoxide, which can poison you.
• Blue smoke: the engine is burning oil. Thick white smoke that doesn't clear once the engine is warm: possibly coolant. Black smoke when accelerating, on a diesel: incomplete combustion or a loaded filter.
• The engine or particulate filter warning light comes on, perhaps with a sudden loss of power (limp mode).
• A smell of sulphur, like rotten eggs: it may come from the catalytic converter or from the way the engine is burning fuel.

The particulate filter and regeneration, explained#

The particulate filter stops soot. To keep it from filling up, the car cleans it itself from time to time: it raises the exhaust temperature and burns off the soot. This is called regeneration, and it needs the right conditions: a warm engine and a few minutes of steady driving, usually out of town.

If you drive almost only short trips around town, regeneration keeps getting interrupted, the filter loads up and the warning light comes on. The manual says what to do then; often, a longer drive at a steady speed. If the light stays on or the car goes into limp mode, go to a garage.

• Signs the car is regenerating, on many models: the fan keeps running after you switch off, the idle is higher. If the manual says so, avoid switching off the engine at that moment.
• The oil matters: many engines with a particulate filter need a specific type of oil. You'll find it in the service book.
• Ash stays behind: over time, ash that doesn't burn builds up in the filter; the garage cleans or replaces it, depending on its condition.
• A filter that keeps clogging has a cause: injectors, the EGR valve, the turbo or a sensor can load the filter faster than normal.

The catalytic converter: what damages it and how to protect it#

A catalytic converter usually lasts a long time, but other engine problems ruin it. Unburnt fuel, for example from a faulty spark plug or ignition coil, overheats it. Oil burnt by the engine or coolant can clog it, and a hard knock under the car can crack it.

• A flashing engine light signals misfires on many cars: ease off and go to a garage, so you don't ruin the converter.
• Don't put off the diagnostics when the engine light stays on: a diagnostic check finds the cause, and a sensor or a coil costs less than a catalytic converter.

The exhaust at the ITP and on the road: what the rules say#

At the ITP, emissions are measured with a gas analyser on petrol cars and an opacity meter on diesels. The EU directive on periodic roadworthiness tests (2014/45/EU), which Romania has written into its ITP rules (RNTR 1), classes these as major deficiencies:

• Emission control equipment fitted by the manufacturer, such as the catalytic converter or the particulate filter, that is missing or obviously defective.
• Leaks that would affect the emission measurement.
• Emissions above the limits that apply to the car.
• Parts of the noise suppression system that are loose, damaged, badly fitted, missing or modified so that the noise goes up. If a part is at risk of falling off, the deficiency is dangerous.

A major deficiency means the car fails the ITP. See also what is checked at the ITP.

On the road too, the Romanian Highway Code (OUG 195/2002) punishes driving a car that makes noise or emits pollutants above the legal limit with a class II fine, that is 4 or 5 fine units (puncte-amendă); one fine unit is 5% of the national gross minimum basic wage. In these cases the police keep the registration certificate (talon) and give you a temporary permit that lets you drive for 15 days.

Removing the particulate filter or the catalytic converter doesn't fix a clogged filter: at the ITP a missing one is a major deficiency, so a fail, and the car pollutes far more. Ask the garage to find out why the filter clogs and to clean or replace it.

What to ask the garage#

1. What they found: which part is faulty, and whether it's repaired or replaced.
2. Why it failed: for a clogged filter or a dead converter, what the underlying engine cause is and whether they'll fix that too.
3. What your options are for the particulate filter: cleaning or replacement, and what they recommend for your car.
4. What warranty they give on parts and labour.

How CariX helps#

In the free driver account you keep your car, its documents and the work done on it in one place.

• The ITP with a reminder: you pick the inspection date and the validity, CariX works out the expiry and emails you 30, 14 and 7 days and 1 day before.
• "Is the price fair?" shows an indicative price range for exhaust work in your city, from the prices businesses list on CariX on their pages and quotes; the real price depends on the car and the parts.
• Warranties: if the garage records a warranty on the job line, in months or kilometres, you see it under "Active warranties" on the car and get an email 30 days before it ends (for a warranty in months).
• The car passport keeps the jobs recorded by garages, with the mileage they confirmed.