BMW 840i Catalytic Converter Replacement Cost

A failing catalytic converter can cause a vehicle to fail emissions tests and turn on the check engine light. The exhaust might have an unusual smell. A restricted catalytic converter can result in a loss of engine power. » LEARN MORE: How to tell if your catalytic converter is failing

If black smoke is coming from the exhaust, you should not drive the vehicle. This would indicate unburned fuel entering the converter, which can damage it.

If the engine is running properly, the catalytic converter should last the life of the vehicle. When it fails, it's commonly caused by too much raw fuel entering the converter, often as a result of a misfiring engine. Too much unburned fuel can coat the catalyst, causing the converter to stop working. The converter can also overheat and break apart inside, becoming restricted or plugged. The catalytic converter is covered by the vehicle's emissions warranty, which extends beyond the manufacturer's factory warranty.  Along with other emission control devices, federal law requires manufacturers to replace a defective converter for up to 15 years or 150,000 miles. Because this coverage varies by state and vehicle type, refer to your owner’s manual for your warranty information.

It depends on the type of failure. If the car is experiencing a loss of power, a back-pressure test can check for a clog. If the check engine light is on, it may include a code that points to the converter. Or, if rattling noises are heard, the technician would need to confirm they are coming from the converter instead of other exhaust components.

It is very important to have the shop identify why the catalytic converter failed. Failure is almost always due to another problem, which if not resolved, will quickly ruin a new catalytic converter.

Most converters are bolted in place in the exhaust system, though some are welded or clamped down. Whatever the case, the converter must be loosened and removed.  Some catalytic converters are built directly into the exhaust manifold, because they work most efficiently when hot. Never touch a catalytic converter while the engine is running or any time soon after it's been shut off.