This procedure covers the removal and replacement of the downpipe (catalytic converter section) on a 2016-2024 Hyundai Tucson with the 2.5L I4 AWD engine, including O2 sensor handling and exhaust system disconnection.

Warnings

Tools required

Parts

• Downpipe gasket (turbo to downpipe) × 1 — Use OEM specification
• Downpipe to midpipe gasket × 1 — Use OEM specification
• Exhaust flange nuts (if corroded) × 4 — M10x1.25 copper lock nuts
• Downpipe assembly with catalytic converter × 1 — Use OEM or 49-state/CARB compliant aftermarket

Preparation

1. Park vehicle on level surface and apply parking brake. Chock rear wheels.
2. Allow exhaust system to cool completely (minimum 2 hours after last engine operation).
3. Apply penetrating oil to all exhaust flange bolts, O2 sensor threads, heat shield bolts, and hanger fasteners. Allow to soak for at least 30 minutes.
4. Raise front of vehicle and support securely on jack stands at manufacturer-specified lift points.
5. Remove engine under covers/splash shields to access downpipe and exhaust components.
6. Disconnect negative battery terminal to prevent O2 sensor fault codes during removal.

Procedure

1. 1

   Remove heat shields
   Locate and remove the heat shields covering the downpipe and catalytic converter. These are typically secured with 10mm bolts. There may be multiple shields covering the turbo downpipe, catalytic converter, and underbody sections. Keep bolts organized for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
2. 2

   Disconnect upstream O2 sensor
   Locate the upstream O2 sensor (between turbo and catalytic converter). Disconnect the electrical connector by pressing the release tab. Using the O2 sensor socket, carefully unthread the sensor counterclockwise. If sensor is seized, apply additional penetrating oil and allow to soak, or use heat carefully. Inspect sensor threads and replace if damaged.
   ⚠O2 sensors are fragile. Avoid applying excessive force which can break the sensor body or damage threads in the downpipe.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
3. 3

   Disconnect downstream O2 sensor (if equipped)
   If your downpipe has a downstream O2 sensor (after catalytic converter), disconnect the electrical connector and remove the sensor using the same technique as the upstream sensor. Not all 2.5L configurations have a downstream sensor on the downpipe.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
4. 4

   Disconnect turbo to downpipe flange
   Locate the connection point between the turbocharger outlet and the downpipe inlet. This is secured by 3 or 4 nuts on studs. Using a 14mm socket, remove the flange nuts while supporting the downpipe. The gasket will likely be stuck; gently pry if necessary. Inspect studs for damage.
   ⚠Turbo outlet studs can break if excessive force is applied to seized nuts. Use penetrating oil liberally and consider heating nuts if severely corroded.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
5. 5

   Disconnect downpipe from midpipe
   Move to the rear connection where the downpipe meets the midpipe/resonator section. This is typically a 2-bolt flange connection. Remove the 14mm or 15mm bolts/nuts securing this flange. Support the midpipe to prevent it from dropping or stressing other hangers.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
6. 6

   Remove exhaust hangers
   The downpipe is supported by 1-2 rubber exhaust hangers. Using an exhaust hanger tool or flat screwdriver, carefully pry the hanger loops off their mounting points. Work the rubber grommet off the hanger rod by pushing the pipe toward the mount to create slack, then pulling the rod out of the grommet.
   ℹ️Inspect rubber hangers for cracks or deterioration. Replace if damaged to prevent future exhaust rattles.
7. 7

   Remove downpipe assembly
   With all connections and hangers released, carefully lower and maneuver the downpipe assembly out from under the vehicle. The catalytic converter section makes this component heavy (20-30 lbs). Be prepared for residual condensation to drain from the pipes. Inspect the removed downpipe for physical damage, internal catalyst deterioration, or cracks.
   ⚠Downpipe assembly is heavy and awkward. Use proper lifting technique and consider having an assistant support the component during removal.
8. 8

   Clean mating surfaces
   Using a wire brush and scraper, thoroughly clean all exhaust flange mating surfaces on the turbo outlet and midpipe connection. Remove all old gasket material, carbon deposits, and corrosion. Clean surfaces ensure proper sealing and prevent exhaust leaks. Inspect flange surfaces for warping or damage.
   ℹ️Do not use excessive force when scraping aluminum flanges as they can be damaged more easily than steel.
9. 9

   Prepare new downpipe
   Unpack the new downpipe and verify it matches the original configuration including O2 sensor bungs, flange positions, and overall length. Install new gaskets on both flanges (turbo and midpipe connections). Apply a thin coat of anti-seize to all flange bolt/stud threads and O2 sensor threads (threads only, not the sensor tip).
   ⚠Never apply anti-seize to O2 sensor tips or contaminate the sensing element. Apply only to threads.
10. 10

    Install new downpipe
    Maneuver the new downpipe into position, aligning the turbo flange first. Hand-thread 1-2 nuts onto the turbo studs to hold position. Align the rear flange with the midpipe and hand-thread those bolts. Install the exhaust hangers by working the rubber grommets onto their mounting rods. With all connections loosely attached, verify proper alignment and clearance from heat-sensitive components, brake lines, and suspension.
    ℹ️Do not fully tighten any fasteners until all connections are aligned and hangers are installed. This allows adjustment for proper fit.
11. 11

    Torque turbo flange connection
    Starting from the center and working outward in a cross-pattern, tighten the turbo to downpipe flange nuts to specification. Use a torque wrench to ensure even clamping force. Verify the gasket is properly seated and not protruding.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
12. 12

    Torque midpipe flange connection
    Tighten the downpipe to midpipe flange bolts to specification in a cross-pattern. Check that the joint is flush and the gasket is properly compressed.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
13. 13

    Install O2 sensors
    Thread the upstream O2 sensor into the downpipe by hand until it bottoms, then use the O2 sensor socket and torque wrench to tighten to specification. Repeat for the downstream sensor if equipped. Connect the electrical connectors firmly until they click. Ensure wiring is routed away from hot exhaust components and has adequate slack for engine movement.
    ⚠Cross-threading O2 sensors will destroy the bung threads. Always start threading by hand and ensure sensor goes in smoothly.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
14. 14

    Reinstall heat shields
    Position all heat shields back in their original locations and secure with the mounting bolts. Ensure shields are not touching the exhaust pipe directly and have proper clearance. Tighten bolts to specification.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)
15. 15

    Final inspection and verification
    Perform a final visual inspection of all connections, verifying no tools or parts were left in the engine bay. Check that all exhaust components have adequate clearance from suspension, driveline, and body components. Reinstall engine under covers. Lower vehicle from jack stands. Reconnect negative battery terminal.

Reassembly

1. Ensure all exhaust connections are torqued to specification before starting engine.
2. Verify O2 sensor electrical connectors are fully seated and wiring is properly routed.
3. Check that heat shields are installed and not rattling against exhaust components.
4. Confirm adequate clearance between downpipe and all surrounding components (minimum 10mm).

Verification

• Start engine and allow to idle. Listen for exhaust leaks at turbo flange and midpipe connection. A hissing sound indicates a leak that must be corrected.
• Check for unusual odors that might indicate exhaust leaks entering the cabin.
• Rev engine to 3000 RPM and verify no rattles, vibrations, or exhaust leaks under load.
• Using an OBD-II scanner, verify no fault codes are present for O2 sensors or catalytic converter efficiency.
• Perform a test drive and verify normal engine performance. Monitor for check engine lights.
• After 50-100 miles of driving, re-inspect all flange connections for signs of leaks (black soot marks) and verify torque on accessible fasteners.
• If check engine light illuminates with catalyst efficiency codes (P0420/P0430), verify proper O2 sensor installation and that CARB-compliant catalytic converter was used if in California or CARB states.

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