// REPAIR GUIDE
Toyota Camry P0420 Catalytic Converter Replacement — Complete DIY Guide
Difficulty Time: 2.5 hrsCost: $300–$700
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Prep & Safety
This job involves working under the vehicle near exhaust components. Allow the exhaust to fully cool for at least 2 hours after driving. Park on a flat surface, chock the rear wheels, and use jack stands rated for at least 2 tons each.
WarningNever work under a vehicle supported only by a jack. Use jack stands. A hydraulic jack can fail without warning.
Removal
1
Disconnect battery and spray penetrant
Disconnect the negative battery cable. Liberally spray PB Blaster on all four cat flange bolts (two upstream, two downstream) and the downstream O2 sensor base. Let it sit for 15 minutes minimum.
2
Remove downstream O2 sensor
Unclip the harness, then back the sensor out with a 22mm O2 socket. If it's seized, run the engine for 5 minutes (warm threads expand and release easier) — but let it cool before continuing.
Pro TipMark the sensor body before removal — if you decide to reuse it after testing, you'll know its original orientation.
3
Unbolt cat flanges
Support the cat with a stand or jack while breaking the bolts loose. Both flanges have two bolts each — work the diagonals back and forth to avoid binding.
TORQUE SPEC (factory):
Cat flange bolts: M10 x 1.25
Torque on removal: N/A (back off in 1/4 turn increments)
Torque on install: 35 ft-lb (47 Nm)4
Lower the cat
Once both flanges are free, the cat will drop. It's heavier than it looks — about 12 lbs on the 4-cyl, 18 lbs on the V6. Don't let it crash onto the subframe.
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Installation
5
Fit the new cat with new gaskets
Always install fresh gaskets — old gaskets are crushed and will leak even if they look fine. Hand-thread all four bolts before tightening any of them.
6
Torque to spec in cross-pattern
Tighten in a star pattern in three passes: 15 ft-lb, 25 ft-lb, then 35 ft-lb final. This prevents warping and ensures even gasket compression.
Pro TipApply nickel-based anti-seize (not copper) to flange bolt threads. Copper anti-seize can affect O2 sensor readings if it migrates.
7
Install the new downstream O2 sensor
Anti-seize the threads only — never the sensor tip. Hand-thread until snug, then 1/4 turn with a wrench. The sensor is sensitive; do not over-torque.
WarningIf the new sensor came pre-coated with anti-seize, do not add more. Excess will smoke off in the exhaust and may contaminate the cat.
8
Reconnect harness and battery
Route the O2 sensor pigtail away from exhaust heat. Reconnect the battery. The first start will be rough for ~10 seconds while the ECM relearns.
Verification
Clear the P0420 code. Take the vehicle on a 20-minute mixed-cycle drive (city + highway) to allow the cat efficiency monitor to run. Hook up your scanner and verify:
MONITOR STATUS:
Catalyst Monitor (Bank 1): COMPLETE ✓
O2 Sensor Monitor: COMPLETE ✓
P0420: NOT PRESENT ✓
FUEL TRIMS:
STFT: ±2.5%
LTFT: ±4.0%If P0420 returns within 100 miles, suspect either a defective new cat (warranty) or an unresolved upstream cause (rich condition, oil consumption).
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