- Exhaust manifold
- Upstream oxygen sensor
- Catalytic converter
- Downstream oxygen sensor
- Resonator
- Muffler
- Tailpipe
Exhaust and emissions
Exhaust leaves the engine through the manifold or header, passes through one or more catalytic converters, then through resonators and a muffler to the tailpipe. Oxygen sensors before and after the converter tell the engine computer how well it is running and whether the converter is working. The evaporative emissions system stores fuel vapor in a charcoal canister and feeds it back to the engine. Exhaust gas recirculation lowers combustion temperature. Diesel engines add particulate filters and fluid-based systems that reduce nitrogen oxides.
Common parts
- EX·1Exhaust manifolds, headers, and manifold gaskets
- EX·2Exhaust pipes, flex pipes, clamps, and hangers
- EX·3Mufflers and resonators
- EX·4Catalytic converters
- EX·5Upstream and downstream oxygen sensors and air-fuel ratio sensors
- EX·6EGR valves, coolers, and tubes
- EX·7EVAP canisters, purge valves, vent valves, and leak detection pumps
- EX·8PCV valves and hoses
- EX·9Diesel particulate filters, exhaust fluid parts, and NOx sensors
Signs of trouble
A loud exhaust, a ticking at cold start that fades as it warms, or a smell of fumes in the cabin can mean a leak. A rattle under the car can be a loose heat shield or a broken converter. A converter code can come from the converter itself, but also from a misfire, an oil-burning engine, or a lazy oxygen sensor, so the cause is worth finding before replacing an expensive part. EVAP codes often trace back to a loose fuel cap or a cracked hose.
Finding the right fit
Converters are certified for particular vehicles. California and several other states require converters approved by the California Air Resources Board for vehicles certified to their standards, and the listing should say so. Federal converters are not legal in those cases. Oxygen sensors differ by position (upstream or downstream, bank one or bank two) and connector, so match the location the code or the lookup names. Removing or defeating emissions equipment is illegal for road vehicles in the United States.
Symptom to part
| What you notice | Usually points at | Check first |
|---|---|---|
| Converter efficiency code | Converter, or a misfire or sensor upstream of it | Fix misfires and check sensor readings before replacing the converter |
| EVAP small leak code | Fuel cap, purge valve, or a cracked hose | Reseat or replace the cap first |
| Ticking at cold start that fades | Manifold or gasket leak | Look for soot at the joint |
| Rattle under the car | Loose heat shield or broken converter substrate | Tap the shield and the converter with the engine off and cool |
Before you order
Start with the year, make, model, and engine, then narrow it down with the trim, drive type, and any option the part depends on. The VIN is the most reliable way to do that, because many parts catalogs and dealer counters decode it to the exact build. If the old part is in hand, its original-equipment number is the best cross-reference. Aftermarket brands publish their own numbers and usually list the original number they replace. Two listings that both say they fit can still differ, so compare the photos, connectors, mounting points, and the notes in the listing. The find the right part guide covers this step, and the all makes reference lists each maker’s official parts catalog.
Once you know the part number, compare the same number across stores. Look past the first price at the core charge, shipping, the return window, and what the warranty covers and who honors it. A remanufactured part, a new aftermarket part, and an original-equipment part can each be the right choice, but they are not the same purchase. The compare prices and warranties guide walks through what to read. Prices on PartIndex carry the date they were recorded, so confirm the current price and fitment with the retailer before you buy.
Exhaust parts get extremely hot and stay hot after the engine is off. Carbon monoxide has no smell, so do not run an engine in a closed space, and fix any leak that lets fumes into the cabin. Support the vehicle on stands, not a jack, before working underneath.