P0402: How to Diagnose & Fix — Exhaust Gas Recirculation Flow Excessive
89 vehicles · 23 makes · $20-$15,000 repair
How to diagnose and fix P0402: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Toyota Tundra · 2007–2021
The 5.7L iForce V8 engine is known for developing oil leaks at the cam tower due to Toyota's use of gray RTV silicone sealant instead of a proper gasket from the factory. The sealant degrades over time, particularly at the rear of the cam towers where the engine is slanted.
Common Symptoms
- Oil residue visible in wheel wells
- Burning oil smell
- Oil spots on driveway
- Low oil level between changes
- Shiny wetness around cam tower area
How to Fix
Repair requires removing the top of the engine, timing chain, and cam tower to reseal with proper RTV. This is labor-intensive and typically costs $2,500-$4,000 at a dealer. DIY is possible for experienced mechanics.
Owner tips & cautions
- TipDIY repairs can save significantly - dealer charges $2,500-$4,000 but DIY costs are typically 50-70% less
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
- TipSearch Toyota Tundra 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
Toyota Prius · 2004–2015
Gen 2 (2004-2009) and Gen 3 (2010-2015) Prius NiMH battery packs commonly fail between 8-15 years. Individual cell degradation causes voltage imbalances, triggering warning lights and reduced performance. Battery cooling fan clogging accelerates failure.
Common Symptoms
- Red triangle warning light
- P0A80 code - Replace Hybrid Battery Pack
- Decreased fuel economy
- Reduced power and acceleration
- Battery SOC fluctuating rapidly
How to Fix
Replace hybrid battery pack or individual failed cells. Toyota OEM pack costs $2,200-$3,500. Refurbished options from Green Bean Battery ($1,500 with warranty) or Dorman (587-001 for Gen 2, 587-003 for Gen 3). DIY cell replacement possible with individual cells ($20-40 each). Clean battery cooling fan first - located behind rear seat on driver side.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Greentec Auto 2004-2009 Prius hybrid battery with new cells
replace a professionally diagnosed failed Gen-2 traction-battery pack as a complete matched assembly Fitment/availability: 2004-2009 Prius Gen 2 NiMH pack, 200 V and 28 modules; confirm VIN, service area, core deposit/return and warranty…
- Greentec Auto 2010-2015 Prius hybrid battery with new cells
replace a professionally diagnosed failed Gen-3 liftback traction-battery pack as a complete matched assembly Fitment/availability: 2010-2015 Prius Gen 3 liftback NiMH pack, 6.5 Ah and 28 modules; not a Prius v or Plug-in pack, and core/…
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Sources for this issue (1)
Nissan Leaf · 2011–2023
The Nissan Leaf uses an air-cooled lithium-ion battery that degrades faster than liquid-cooled competitors. Hot climates (Arizona, Texas) accelerate degradation significantly. Early models (2011-2015) with 24 kWh packs can lose 30-40% capacity within 5-7 years. Nissan provides an 8-year/100,000-mile battery warranty covering loss below 9 bars (approximately 66% capacity) on the dashboard gauge.
Common Symptoms
- Range decreasing over time
- Battery capacity bars disappearing on dashboard
- Reduced range in hot weather
- Battery temperature warning
- Rapid charging speed declining
How to Fix
Monitor battery health using LeafSpy app and OBD2 adapter. Keep battery between 20-80% charge for daily use. Avoid frequent DC fast charging. Park in shade in hot climates. If below 9 bars within warranty period, Nissan will replace battery modules. Aftermarket battery replacement/upgrade available from $5,000-8,000.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- LELink² configurable Bluetooth Low Energy OBD-II adapter KSO1702
Configure its auto-off behavior, do not leave an unverified adapter powered indefinitely, and do not use it to perform high-voltage repair or to promise warranty approval.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Volkswagen Golf · 2008–2020
Ford F-250 Super Duty · 2011–2019
Find P0402 by make
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P0402 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 P0402 mean?
P0402 stands for "Exhaust Gas Recirculation Flow Excessive." P0402 means the Exhaust Gas Recirculation (EGR) system is flowing too much exhaust back into the intake. The EGR system intentionally routes a small amount of inert exhaust gas into the engine to lower combustion temperatures and reduce nitrogen-oxide emissions, but the flow must be metered precisely. When the PCM determines the flow is excessive — often because the EGR valve is stuck open or letting gas through when it shouldn't — it sets this code. Too much EGR can cause rough idle, stalling, hesitation, and a check engine light.
What are the most common causes of P0402?
The most common causes of P0402 are: EGR valve stuck open or not closing fully, Failed or sticking EGR valve diaphragm/solenoid, Carbon buildup holding the EGR valve open, Faulty EGR position or differential pressure (DPFE) sensor, Leaking EGR valve gasket or pintle seat, Vacuum control or solenoid fault commanding EGR open, Wiring or connector problems in the EGR control circuit. The specific cause varies by vehicle.
How much does it cost to fix P0402?
Repair costs for P0402 range from $20 to $15,000, depending on the vehicle and root cause.
Which vehicles are affected by P0402?
Au7o has documented P0402 across 89 vehicle models from 23 manufacturers: Audi, BMW, Chrysler, Dodge, Ford, GMC, Honda, Hyundai, Jaguar, Jeep, Kia, Land Rover, Mazda, Mercedes-Benz, Nissan, Opel, RAM, SEAT, Skoda, Subaru, Toyota, Volkswagen, Volvo.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.