P0420 on a 2013 Ram 1500
P0420 means the downstream oxygen sensor pattern suggests the bank 1 catalytic converter is not storing oxygen properly.
Not your vehicle? See general P0420 info.
Most common causes on the 2013 Ram 1500
Ranked from 1,254 NHTSA owner complaints filed for this vehicle.
- 1
Camshaft/lifter failure driving chronic misfires that overheat the catalytic converter
High severityThis 5.7L Hemi has a widely-reported cam-and-lifter failure (oil-starvation related) producing rough running, ticking, and cylinder misfires (P0300/P0303 seen in this batch); sustained misfires push unburned fuel into the exhaust and can overheat/damage the cat substrate.
Reported in 11 NHTSA complaints - 2
Broken/loose exhaust manifold bolts causing a pre-cat exhaust leak
High severityA well-documented failure on the 5.7L Hemi in this generation: warped manifolds shear the retaining bolts, opening an exhaust leak ahead of the downstream O2 sensor that skews the catalyst efficiency reading -- repeatedly described here as a known, common issue.
Reported in 6 NHTSA complaints - 3
Failing downstream (rear) oxygen sensor
Medium severityOwner reported needing to replace the O2 sensor after an engine overhaul that also required addressing check-engine codes -- a degraded rear sensor can mimic low catalyst efficiency.
Reported in 1 NHTSA complaintParts:oxygen sensor - 4
Ignition misfire from worn spark plugs or coil packs
Medium severitySame owner replaced plugs and a coil pack for a check-engine light before a full engine overhaul, consistent with ignition-side misfire fouling the catalyst.
Reported in 1 NHTSA complaint - 5
Worn or aged catalytic converter
Medium severityCatalyst efficiency naturally degrades with mileage until it falls below the OBD-II threshold.
Common causeParts:catalytic converter - 6
Exhaust manifold gasket or pipe leak ahead of the sensor (general wear)
Medium severityBeyond the bolt-shearing failure mode, ordinary gasket wear at manifold-to-pipe joints ahead of the sensor is a standard P0420 contributor.
Common causeParts:exhaust gasket
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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0420 on your car still needs shop confirmation before any repair.
Common symptoms
- Check engine light
- Usually no drivability issue
- Failed emissions test
- Sulfur smell in some cases
- Reduced power if converter is clogged
What to check before replacing parts
Check for misfire and fuel trim codes first
Look for: Any active or recent misfire, or lean/rich trim codes, means raw fuel or an off mixture has likely already damaged or is currently overworking the converter — fix those before touching the catalyst.
Inspect for exhaust leaks ahead of the converter
Look for: A leak before the converter (cracked manifold, loose flange, blown gasket) lets in outside air that confuses the downstream O2 sensor into reading as if the catalyst isn't working, even when it is.
Compare upstream and downstream O2 sensor activity
Look for: A healthy converter makes the downstream sensor read flat and steady while the upstream sensor swings actively. If the downstream sensor switches nearly as fast as the upstream one, the converter isn't storing oxygen properly and is likely worn out.
Check converter temperature and performance
Look for: A converter outlet noticeably cooler than expected relative to its inlet under load suggests little catalytic reaction is happening inside — supports a genuinely failed converter rather than a false reading.
Hold off on replacing the converter until root causes are ruled out
Look for: If misfires, exhaust leaks, or fuel trim issues caused this code, a new converter will fail again quickly — confirm those are clean first.
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