How to replace the catalytic converter — Nissan Altima 2020

Tools you'll need

• Ratchet
• 12 mm and 14 mm sockets
• Extension bars
• Oxygen sensor socket (22 mm)
• Torque wrench
• Penetrating oil
• Gasket scraper

Parts you'll need

• New direct-fit catalytic converter (manifold converter assembly for the 2.5L)
• New exhaust manifold gasket
• New downpipe gasket
• New exhaust nuts and bolts
• Penetrating oil

Steps

1. Let the exhaust cool and disconnect the batteryPark on a flat surface, set the parking brake, and let the engine and exhaust cool completely. Disconnect the negative battery terminal.
2. Remove the heat shield and both oxygen sensorsRemove the heat shield bolts and lift the shield off the exhaust manifold. Then unplug both oxygen sensors and unscrew them with an oxygen sensor socket so they are out of the way.
   Tip: Label the two oxygen sensors so each one goes back in the same hole it came from.
3. Soak all the exhaust nuts with penetrating oilSpray penetrating oil on every exhaust manifold nut and on the bolts where the converter meets the downpipe. Let it soak for at least 15 minutes, and spray it again if the nuts look rusty.
   Tip: Rusty exhaust nuts snap easily. Soaking them and working them back and forth is far better than forcing them in one pull.
4. Unbolt the converter from the downpipe and the headUnbolt the converter from the downpipe first, then remove the manifold nuts from the cylinder head. Support the converter as the last nut comes off so it does not drop.
5. Remove the old converter and clean the gasket surfacesPull the old converter assembly out and set it next to the new one to confirm the shape, flanges, and sensor holes match. Scrape the old gasket material off the cylinder head and the downpipe flange until both surfaces are clean.
6. Install the new converter with new gasketsFit the new manifold gasket onto the cylinder head studs, set the new converter in place, and start all the nuts by hand. Tighten them in a criss-cross pattern to the torque in your manual, then bolt the downpipe flange up with its new gasket.
7. Refit the oxygen sensors and heat shieldRefit both oxygen sensors into their original holes, tighten them to about 33 ft-lb, and plug their connectors back in. Refit the heat shield.
8. Start the engine and check for leaksReconnect the battery and start the engine. Listen for an exhaust leak, which sounds like a loud ticking or puffing near the manifold. The check engine light may stay on for a few drive cycles while the computer tests the new converter. If the light comes back after a few days, have the codes read to confirm the repair.

Safety first

Let the exhaust cool completely before you work on it. Use a legal, emissions-compliant catalytic converter for your state; a straight pipe or a non-compliant converter is illegal and will fail inspection. In California, the replacement must be CARB-approved. If you are not confident, have a qualified technician do this job.