Catalytic Converter - California

Remove and replace the California emissions-compliant catalytic converter assembly on a 2021-2024 Ford F-150 3.5L EcoBoost RWD.

Warnings

Tools required

Parts

• California emissions catalytic converter assembly × 1 — Use OEM or CARB-certified aftermarket
• Exhaust flange gasket set × 1 — Use OEM specification
• Exhaust manifold gaskets (if disturbed) × 1 — Use OEM specification
• Oxygen sensors (if damaged or over 100k miles) × 2 — Use OEM specification

Preparation

1. Allow exhaust system to cool completely (minimum 2 hours after last operation)
2. Raise vehicle on lift or secure on jack stands at proper lift points
3. Spray all exhaust flange bolts, oxygen sensor threads, and hanger bolts with penetrating oil and allow to soak 15-30 minutes
4. Disconnect negative battery terminal to prevent O2 sensor codes during service
5. Take photographs of oxygen sensor wire routing and heat shield positions for reference

Procedure

1. 1

   Remove heat shields
   Locate and remove the catalytic converter heat shields. These are typically held by 10mm bolts. Remove all heat shield bolts and carefully lower shields away from converter assembly. Inspect shields for damage and replace if severely corroded.
   Torque spec

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

   Disconnect upstream oxygen sensors
   Locate the two upstream oxygen sensors on the catalytic converter assembly. Disconnect the electrical connectors by pressing release tabs. Using the oxygen sensor socket, carefully unthread sensors by turning counterclockwise. If sensors are seized, apply heat (not exceeding 150°C) to the bung area while applying steady pressure. Do not force rotation.
   ⚠Oxygen sensors are fragile and expensive. If sensor will not rotate after moderate force, apply additional penetrating oil and wait before trying again.
   Torque spec

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

   Disconnect downstream oxygen sensors
   Locate downstream oxygen sensors after the catalytic converter. Disconnect electrical connectors and remove sensors using the oxygen sensor socket. Keep upstream and downstream sensors separated and labeled for reinstallation in correct positions.
   Torque spec

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

   Support catalytic converter assembly
   Position a transmission jack or exhaust support stand under the catalytic converter assembly to support weight during removal. Adjust height to take slight pressure off hangers and flanges without forcing components.
5. 5

   Remove upstream exhaust flange connection
   Locate the flange connection between the turbocharger downpipes and catalytic converter inlet. Remove the flange bolts (typically 3-4 bolts per side). Keep bolts organized for reuse if in good condition. Gently separate flange and remove old gasket material.
   Torque spec

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

   Remove downstream exhaust flange connection
   Locate the flange connection at the rear of the catalytic converter assembly where it connects to the mid-pipe. Remove all flange bolts. If bolts are heavily corroded, apply penetrating oil and use impact wrench for removal. Remove old gasket material from flange surface.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
7. 7

   Release exhaust hangers
   Locate rubber exhaust hangers supporting the catalytic converter assembly (typically 2-4 hangers). Use exhaust hanger removal tool or pry bar to carefully pop rubber isolators off their mounting studs. Work systematically from front to rear to prevent binding.
   Torque spec

   Hanger Bolts23 Nm (17 lb-ft)
8. 8

   Remove catalytic converter assembly
   With all connections released, carefully lower the catalytic converter assembly using the support jack. Maneuver assembly around crossmembers and steering components. Guide oxygen sensor wiring through chassis during removal. Inspect mounting points and hangers for damage.
9. 9

   Clean and inspect flange surfaces
   Use wire brush to thoroughly clean all flange mating surfaces on turbocharger downpipes and mid-pipe. Remove all old gasket material, carbon deposits, and corrosion. Inspect flange surfaces for warping or cracks. Check stud condition and replace any damaged studs before proceeding.
10. 10

    Prepare new catalytic converter
    Unpack new California CARB-certified catalytic converter and verify it includes all necessary hardware and gaskets. Transfer oxygen sensors from old converter to new converter if reusing (apply anti-seize to threads only, avoiding sensor element). If installing new sensors, apply anti-seize to threads only. Install sensors hand-tight, then torque to specification.
    ⚠Never apply anti-seize to oxygen sensor element. Only apply to threads. Contamination of sensor element will cause false readings.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
11. 11

    Install new catalytic converter assembly
    Position new converter assembly on support jack and maneuver into position. Route oxygen sensor wiring through chassis openings as documented in preparation photos. Align converter with upstream and downstream flanges. Install exhaust hangers onto rubber isolators, working from rear to front.
12. 12

    Install upstream flange connection
    Position new exhaust gasket on turbocharger downpipe flange. Align catalytic converter inlet flange and install bolts finger-tight. Apply anti-seize compound to bolt threads as specified. Once all bolts are started, torque in a cross-pattern to specification.
    Torque spec

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

    Install downstream flange connection
    Position new exhaust gasket on catalytic converter outlet flange. Align mid-pipe flange and install bolts finger-tight. Apply anti-seize compound to bolt threads as specified. Torque bolts in cross-pattern to specification. Verify all exhaust hangers are properly seated.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
14. 14

    Connect oxygen sensors and install heat shields
    Reconnect all oxygen sensor electrical connectors, ensuring proper routing away from hot exhaust components and moving parts. Verify connectors are fully seated with positive click. Reinstall heat shields in original positions and torque mounting bolts to specification.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

1. Reconnect negative battery terminal
2. Before lowering vehicle, visually inspect all connections and verify no tools or parts remain in work area
3. Lower vehicle and perform final visual inspection of exhaust system alignment

Verification

• Start engine and allow to idle. Listen for exhaust leaks at all flange connections (hissing or ticking sounds indicate leak)
• Inspect all connections while engine is running for visible exhaust gas escape
• Rev engine to 2000-2500 RPM and verify no rattles or abnormal exhaust noises
• Check oxygen sensor data using OBD-II scanner to verify all sensors are reporting proper voltage transitions
• Clear any diagnostic codes and perform test drive to verify check engine light does not return
• After test drive, perform final inspection of all bolted connections while exhaust is warm to check for any weeping or loosening

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