P0420 on Honda: How to Diagnose & Fix

How to Fix

Honda released a software update (PCM update) that raises engine operating temperatures faster and increases idle RPM in cold conditions. For 2017-2018 models, Honda also extended the powertrain warranty by one year. Owners should change oil more frequently (every 3,000-5,000 miles) in cold climates.

Owner tips & cautions

• WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
• TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
• TipSearch Honda CR-V forums and owner groups for real-world experiences and DIY guides
• TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair

How to Fix

Install VCM disable device (VCMuzzler, VCMTuner) which prevents cylinder deactivation and stops oil consumption. Replace fouled spark plugs after installing disabler. Honda settled class-action providing 8-year warranty extension for engine misfire repairs. Severe cases may require piston ring replacement ($3,000-$5,000). 2014+ models received redesigned engine without VCM.

Owner tips & cautions

• TipCheck oil level every fuel fill-up on VCM-equipped models - carry a quart of oil in the van
• WarningDon't ignore misfire codes - prolonged misfires destroy catalytic converters ($2,000+ repair)

How to Fix

Disable VCM using aftermarket devices: VCMuzzler II ($81), VCMTuner II ($150-200), or S-VCM Controller ($180-250). Check oil level every 500-1,000 miles and top off as needed. Use synthetic 0W-20 oil. Replace spark plugs every 30k-50k miles instead of 100k. Severe cases may need engine rebuild ($4,000-$8,000).

Owner tips & cautions

• TipDisabling VCM reduces damage to engine mounts ($800) and minimizes transmission torque converter wear
• TipCheck oil level every 500-1,000 miles and keep 2-3 quarts of oil in vehicle for top-offs
• WarningDo not ignore excessive oil consumption - running engine low on oil can cause catastrophic engine failure

How to Fix

Visit Honda dealer for diagnosis using TSB 20-100. For vehicles with these codes, Honda will replace fuel injectors and catalytic converters under extended warranty (10 years/150,000 miles for 2016-2017). PCM software update also available. Keep documentation of all misfires and check engine lights to support warranty claim.

Owner tips & cautions

• TipHonda extended warranty to 10 years/150,000 miles for 2016-2017 models with these codes - document all issues
• TipIf dealer denies warranty claim, reference TSB 20-100 specifically and escalate to Honda corporate
• WarningDo not ignore misfire codes - continued driving can damage catalytic converters ($1,500-$3,500 to replace)
• WarningThese codes often misdiagnosed as VCM issues - verify with dealer using TSB 20-100 for correct diagnosis

How to Fix

Diagnose before replacing: verify upstream/downstream O2 sensor behavior and rule out injectors (especially 2016-2018) and exhaust leaks. If the converter is genuinely failed, replace with an OEM or CARB-compliant unit for the affected bank. Address any root cause (oil consumption/VCM, misfires, rich condition) so the new converter is not damaged.

How to Fix

Replace the cracked front pipe with a Walker or Bosal aftermarket unit, or have a muffler shop weld in a proper stainless flex section. Address worn engine/transmission mounts at the same time to prevent premature re-failure. Expect rusty flange bolts that may snap and need to be cut/replaced.

How to Fix

Install VCM disabler device: VCMuzzler II (~$81, simplest install, no power wire), VCMTuner II ($150-200, more features), or S-VCM Controller ($180-250, automatic temperature adjustment). Check oil every 500-1,000 miles until VCM disabled. Replace fouled spark plugs with NGK DILKAR7B11 ($5-8 each) every 30,000-50,000 miles. Honda 2016 class action settlement may provide extended warranty for misfires/consumption - contact Honda with VIN. Severe cases (catalytic converters destroyed): $2,000-3,500 replacement.

How to Fix

Do not blindly replace the converter. First verify no misfire, no excessive oil consumption, and confirm the rear (downstream) O2/AFR sensor is healthy with live data — a slow-switching rear sensor causes false P0420. If oil consumption is the root cause, fix that first or the new cat will fail again. If the catalyst is genuinely spent, replace with an OEM or CARB-compliant direct-fit converter (V6 requires the correct bank). OEM converters are expensive; quality aftermarket units cost far less.

How to Fix

Confirm consumption with a Honda oil-consumption test (measured top-up over a set mileage). Affected 2008-2011 L4 vehicles within 8yr/125k qualify for free piston and ring replacement under the warranty extension (TSB 13-077); a software/PCM update for the oil-consumption-reduction logic is applied alongside. Out-of-warranty, the durable fix is replacing pistons and oil control rings (approx. 1,200-2,800 USD); some owners get partial relief from a top-engine carbon clean and shorter 5,000-mile oil intervals using Honda 0W-20 full synthetic, but ring replacement is the only permanent repair.

How to Fix

For oil consumption: Monitor oil level every 1,000 miles and keep records with dates/mileage for warranty documentation. Honda requires documented consumption test (typically 1,000-mile monitoring period) to approve engine work. TSB 22-078 addresses ring seating with specific break-in oil change at 5,000 miles using Honda Genuine 0W-20. For phantom braking: Dealer can recalibrate Honda Sensing radar sensor (free under warranty, TSB references available). Persistent AEB issues may require radar sensor replacement ($200-400 under warranty). File NHTSA complaint at nhtsa.gov to support recall investigation.

Owner tips & cautions

• TipCivicX.com 11th gen owners: Document EVERY oil check with date, mileage, and amount added - Honda requires formal consumption test documented over 1,000 miles to approve warranty engine work
• TipFor phantom braking: Reference NHTSA investigation PE22-029 when requesting Honda Sensing recalibration at dealer - shows Honda the federal investigation and often results in free repairs beyond warranty
• WarningPhantom braking at highway speeds is extremely dangerous - document all incidents with GPS location, time, weather conditions and file NHTSA complaint at nhtsa.gov; this is how recalls get initiated

How to Fix

Replace the manifold. Options include an OEM manifold, a two-piece Dorman replacement, a Walker manifold/cat combo, or an aftermarket header. Welding is generally not recommended as repairs rarely hold on the thin cracked casting.

How to Fix

Disable VCM using aftermarket devices: VCMuzzler II ($81), VCMTuner II ($150-$200), or S-VCM Controller ($180-$250). Check oil level every 500-1,000 miles until VCM disabled. Use synthetic 0W-20 oil. Replace spark plugs every 30,000-50,000 miles instead of 100,000. Severe engine damage may require rebuild ($4,000-$8,000).

Owner tips & cautions

• TipMonitor oil level obsessively and keep 2-3 quarts in vehicle for top-offs between oil changes
• WarningInstall VCM disabler as preventive measure, not reactive - engine damage from oil consumption is permanent and expensive
• TipReplace spark plugs every 30k-50k miles instead of 100k - fouled plugs cause misfires that damage catalytic converters ($1,500-$3,500)
• TipDisabling VCM also protects engine mounts and transmission from excessive wear and vibration

How to Fix

Switch to full synthetic Mobil 1 5W-20 (community standard). Change oil every 5,000 miles (not 7,500). Use high-quality oil only (Mobil 1, Honda HG, Pennzoil). Monitor and top off between changes. No permanent fix for late-stage consumption - keep oil topped off and change regularly.

Owner tips & cautions

• TipChange oil every 5,000 miles (not 7,500) to prevent oil consumption from developing
• WarningAvoid cheap or wrong viscosity oil at any cost - causes stuck oil control rings and consumption
• TipElement owners consistently report 200k+ miles when using quality synthetic oil and regular changes
• TipNo permanent fix for late-stage oil consumption - monitor oil level weekly and keep topped off

How to Fix

Prevention (before damage): Install VCM Muzzler II ($170-200) to disable VCM system - CrosstourOwnersClub.com members report oil consumption drops to normal levels. Monitor oil level weekly and top off as needed. Severe damage: Engine rebuild ($4,000-6,000) or replacement ($6,000-8,000). Honda may cover under goodwill if under 100k miles - document all oil consumption and dealer visits. Switch to 0W-20 or 5W-30 synthetic oil - some owners report reduced consumption.

Owner tips & cautions

• WarningCRITICAL: Check oil level EVERY WEEK - running low on oil will destroy engine ($6k+ replacement). Low oil light means you're already dangerously low.
• TipDocument EVERYTHING - every quart of oil added, dealer visits, complaints. Honda may offer goodwill engine replacement if you have documentation.
• Tip2013+ Crosstour has J35Y1 engine without VCM oil consumption issues - if buying used, get 2013 or newer to avoid this problem.

How to Fix

Confirm the leak with a cold-start inspection, smoke test, or by checking for soot around the manifold flange and studs. Replace broken studs, resurface or replace the manifold if warped, and install new gaskets and hardware. Penetrating oil, heat, and careful extraction are often required to avoid cylinder-head damage.

How to Fix

Replace catalytic converter with OEM Honda ($1,200-2,000) or high-quality aftermarket like MagnaFlow or Walker ($400-800). Cheap universal cats won't last on lean-burn engine. Address root cause: clogged EGR system can overheat and kill cat - clean EGR before replacing cat. InsightCentral recommends MagnaFlow Direct-Fit cats - last 100k+ miles.

Owner tips & cautions

• WarningClean EGR system BEFORE replacing cat - clogged EGR overheats and kills new cats within 10k miles. Fix the root cause first.
• TipAvoid ultra-cheap universal cats ($150-250) - they won't pass emissions on lean-burn Insight and fail quickly. Spend $400+ for direct-fit.