P0420 on Jeep: How to Diagnose & Fix
Catalyst System Efficiency Below Threshold (Bank 1)
6 Jeep models · 7 documented issues · 2 critical · $50-$8,500 repair
P0420 on Jeep by model: symptoms, diagnosis and fix
The 2.4L Tigershark MultiAir engine suffers from defective piston rings allowing oil to burn in combustion chamber. Owners report consuming 1 quart per 1,000 miles. Engine can stall when oil falls below 3.5 quarts without warning light.
Common Symptoms
- Consuming 1+ quart of oil every 1,000-2,000 miles
- Engine stalling without warning
- Oil light only after engine stalls
- Blue smoke from exhaust during acceleration
- Rough idle or misfires
How to Fix
FCA Warranty Extension XB1 covers excessive oil consumption for 7 years/100,000 miles. Engine recalibration/PCM software update can reduce consumption. Severe cases require engine replacement or rebuild with updated piston rings.
Owner tips & cautions
- WarningCheck oil level every 500-1,000 miles religiously
- TipDocument oil consumption with receipts for warranty claims
Sources for this issue (5)
- Valero Law: Class-Action over FCAs Tigershark Oil Consumption Defectmedia
- MyCarVoice: Fiat Chrysler 2.4L Tigershark Engine Class Action Settlement Announcedmedia
- Jeep Renegade Forum: 2.4L Tigershark Class Action Lawsuit and Oil Consumption Issuesforum
- The Lemon Firm: Jeep Cherokee 2.4L Tigershark Oil Consumption Causes Engine To Stallmedia
- Sauder Schelkopf: Jeep Excessive Engine Oil Consumption Class Action Investigationmedia
The 2.4L Tigershark MultiAir engine consumes oil at an abnormal rate, sometimes exceeding 1 quart per 1,000-2,000 miles. The MultiAir valve actuation system uses engine oil to operate the intake valves, and the system can develop internal leaks. Worn piston rings and valve seals also contribute. If oil level drops too low, the engine may stall or suffer catastrophic damage.
Common Symptoms
- Oil level drops significantly between changes
- Low oil pressure warning light
- Blue/gray smoke from exhaust
- Engine ticking or knocking at startup
- Check engine light for misfire codes
- Oil smell in cabin or under hood
How to Fix
Monitor oil level every 500-1,000 miles and top off as needed. If consumption exceeds 1 quart per 2,000 miles, have dealer perform an oil consumption test (typically requires 2-3 visits over 3,000 miles). Extended warranty may cover engine replacement if consumption is deemed excessive. Use only 0W-20 full synthetic oil. For high-mileage engines, switching to a high-mileage formulation (Valvoline MaxLife 0W-20) may reduce consumption slightly.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Pennzoil Platinum full-synthetic SAE 0W-20 motor oil, five quartsOEMPennzoil 550046127 / AutoZone 427013
Correct-specification oil for normal service and measured top-up while an owner or dealer documents consumption Fitment/availability: Renegade 2.4L requiring API-certified SAE 0W-20 meeting FCA MS-6395. Fill only to the dipstick/owner-ma…
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Owner tips & cautions
- WarningCheck oil level every 1,000 miles minimum - the 2.4L Tigershark is a known oil consumer and running low will cause engine seizure
- TipDocument all oil consumption with receipts and records - needed if pursuing warranty engine replacement claim
Sources for this issue (2)
The cast iron exhaust manifold on the 4.0L AMC/Jeep inline-6 engine is prone to cracking from thermal stress cycling. The manifold design does not accommodate thermal expansion well, and cracks develop between the exhaust ports, typically between cylinders 3-4 or 5-6. Cracked manifolds cause exhaust leaks that are loudest on cold startup and may quiet down as the manifold expands when hot. The exhaust leak can cause a ticking or hissing sound that is often mistaken for a lifter or valve issue. Broken exhaust manifold bolts are extremely common and can complicate the repair.
Common Symptoms
- Ticking or hissing exhaust leak noise, loudest on cold startup
- Exhaust smell in engine bay or cabin
- Reduced engine performance
- Check engine light with catalyst efficiency codes
- Noise diminishes as engine warms up
How to Fix
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Dorman Renix 4.0L exhaust-manifold kitOEMDorman 674-170 / ATP 101111
A confirmed cracked/leaking exhaust manifold on a 1990 Comanche 4.0L retaining its Renix emissions and sensor configuration Fitment/availability: 674-170 is explicitly listed for the 1990 Comanche 4.0L and interchanges ATP 101111/OE 5300…
- Dorman High Output 4.0L tubular exhaust-manifold kitOEMDorman 674-196 / OE 4883385
A confirmed cracked/leaking exhaust manifold on a 1991-1992 Comanche 4.0L High Output engine Fitment/availability: 674-196 explicitly fits 1991-1992 Comanche 4.0L and includes manifold, gasket, flange and hardware.
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FCA TSB 18-001-26 covers a 2018 WK Grand Cherokee equipped with the 6.2L supercharged ESD engine and 8HP95 DFS transmission when P0420 and/or P0430 is stored. A customer may also report reduced engine power associated with catalyst damage and restricted exhaust flow. The bulletin identifies PCM software as the cause addressed by its repair procedure. It does not apply to the 3.6L Pentastar population in the old card and does not name an upstream or downstream oxygen sensor as the repair.
Common Symptoms
- Malfunction indicator lamp with P0420 and/or P0430
- Possible reduced engine power if catalyst damage has restricted exhaust flow
How to Fix
Confirm the vehicle is a covered 2018 WK with engine sales code ESD and transmission sales code DFS, save the DTC and freeze-frame information, and check the VIN and current calibration level. Follow FCA TSB 18-001-26: maintain the specified battery voltage, reprogram the PCM with the latest software using wiTECH or equivalent, and clear DTCs set during programming. If P0420/P0430 returns, exhaust restriction or loss of power remains, or other DTCs are present, continue with the current factory catalyst, fuel-control, misfire, exhaust-leak, and sensor diagnostics for the exact vehicle. Do not buy oxygen sensors or catalytic converters from the code alone.
Owner tips & cautions
- WarningDo not use this bulletin on a 3.6L Grand Cherokee. Its exact scope is the 2018 6.2L supercharged ESD/8HP95 DFS application.
- TipAsk the shop to record the original calibration, completed flash, cleared DTCs, and post-flash result before any catalyst or sensor purchase is discussed.
Sources for this issue (1)
The 4.7L V8 used in Grand Cherokee models is widely reported to develop broken exhaust manifold bolts or warped manifold sealing surfaces, especially after repeated heat cycles. Owners typically notice a ticking noise on cold start that may quiet as the engine warms, sometimes mistaken for valvetrain noise. Left unrepaired, the leak can worsen and may contribute to exhaust odor or failed emissions inspection.
Common Symptoms
- Ticking noise on cold start
- Exhaust smell in engine bay
- Soot near exhaust manifold
- Noise decreases as engine warms
- Possible emissions test failure
How to Fix
Confirm the leak with a cold-start inspection, listening near the manifold and checking for soot around the flange and broken fasteners. Repair usually involves extracting broken studs/bolts, resurfacing or replacing the manifold if warped, and installing new hardware and gaskets. Penetrating oil, heat, and careful extraction are often required because broken fasteners in the cylinder head are common.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Crown 53034029K left-and-right exhaust-manifold gasket setOEMCrown 53034029K
Manifold-to-head reseal after the leak side is confirmed and the manifold is removed Fitment/availability: Pair of MLS gaskets cataloged for 1999-2007 Grand Cherokee 4.7L. Confirm VIN and current left/right supersessions; this link does …
- Dorman 674-908 WJ driver-side exhaust-manifold kitOEMDorman 674-908 / OE 53030933AB
Driver-side manifold replacement only when the 1999-2004 WJ manifold is warped or cracked Fitment/availability: Exact 1999-2004 Grand Cherokee 4.7L driver-side kit with gasket and downpipe hardware. Not for 2005-2009 WK and not needed fo…
- Dorman 674-907 WJ passenger-side exhaust-manifold kitOEMDorman 674-907 / OE 53030934AB
Passenger-side manifold replacement only when the 1999-2004 WJ manifold is warped or cracked Fitment/availability: Dorman's application is 1999-2004 Grand Cherokee and the kit includes gasket/downpipe hardware. Not for 2005-2009 WK.
- Crown 53013598AB WK passenger-side exhaust manifoldOEMCrown 53013598AB
Confirm VIN and gasket/hardware separately; not for WJ or revised 2008-2009 4.7L.
- Crown 53013599AB WK driver-side exhaust manifoldOEMCrown 53013599AB
Confirm VIN and gasket/hardware separately; not for WJ or revised 2008-2009 4.7L.
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Owner tips & cautions
- TipOwners recommend replacing all manifold hardware on the affected side once one bolt breaks, rather than only the visibly failed fastener.
- TipA smoke test or cold-start stethoscope check helps distinguish manifold leaks from injector or valvetrain noise.
Sources for this issue (1)
TJ Wranglers with the 4.0L frequently develop catalytic converter deterioration, especially on higher-mileage vehicles and 2000-2006 emissions configurations using multiple converters/pre-cats. Owners commonly report a check-engine light with catalyst-efficiency codes, sulfur smell, rattling substrate, or loss of power if the converter begins to clog. This issue is well documented in owner complaints, repair databases, and Jeep service information.
Common Symptoms
- Check engine light
- P0420 or catalyst efficiency codes
- Rattling from catalytic converter
- Sulfur or rotten egg smell
- Reduced power at higher RPM
- Failed emissions inspection
How to Fix
Diagnosis involves checking for P0420/P0432-type efficiency codes, verifying upstream engine tune issues are not causing converter damage, and measuring exhaust backpressure or temperature differential if restriction is suspected. Repair is replacement of the failed converter assembly and any lazy O2 sensors if needed. Misfires, oil burning, or rich-running conditions should be corrected first so the new converter is not quickly damaged.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- MagnaFlow MF23297 Federal/EPA direct-fit rear catalytic-converter assemblyOEMMagnaFlow 23297 / etrailer MF23297
Not CARB compliant and retailer states it cannot be shipped to or used in California, Colorado, Maine or New York; verify the emissions labe
- aFe Power 47-48003 Federal direct-fit front catalytic-converter assemblyOEMaFe Power 47-48003 / Quadratec 17121-1000
Confirm wheelbase, emissions l
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P0420 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0420 mean on a Jeep?
P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)." P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault. On Jeep it is documented across 6 models: Cherokee, Renegade, Comanche, Grand Cherokee, Wrangler, Compass.
What are the most common causes of P0420?
The most common causes of P0420 are: Worn-out or failing catalytic converter (Bank 1), Faulty or aged downstream (or upstream) oxygen sensor, Exhaust leak before or near the oxygen sensors, Engine running rich or lean (fuel trim issues), Misfires or oil/coolant contaminating the converter, Damaged or aftermarket low-quality catalytic converter, Faulty oxygen sensor wiring or connectors, Software/calibration needing update (on some vehicles). The specific cause varies by vehicle.
How much does it cost to fix P0420 on a Jeep?
Published repair estimates on Jeep range from $50 to $8,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0420 on a different make?
View P0420 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.