P0402: How to Diagnose & Fix — Exhaust Gas Recirculation Flow Excessive
34 vehicles · 15 makes · $50-$5,000 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.
Ford F-250 Super Duty · 2011–2019
The EGR (Exhaust Gas Recirculation) cooler on 2011-2019 6.7L Power Stroke diesel engines is prone to clogging with soot and eventually failing, particularly on trucks used for highway driving, light loads, or trucks that idle extensively. The EGR cooler recirculates cooled exhaust gas back into the intake to reduce NOx emissions. Over time, soot accumulates in the cooler's internal passages and restricts exhaust gas flow through the cooler core, and a cooler that overheats can fail. When it fails, exhaust gases enter the coolant system, causing overheating and "puking" coolant from the degas bottle. The 2011-2014 models are particularly susceptible due to narrow internal coolant passages. Ford TSB 13-6-5 (superseding 12-6-14) covers 2011-2012 6.7L trucks with DTC P0401 and P2457, calling for EGR cooler core replacement under normal New Vehicle Limited Warranty coverage. The EGR cooler for 2011-2016 is OEM part BC3Z-9V425-A; 2017+ is HC3Z-9V425.
Common Symptoms
- Coolant loss with no visible external leak
- Coolant reservoir overflows or "pukes" coolant
- White smoke from exhaust (coolant in combustion)
- Engine overheating warning
- DTC codes P0401 (Insufficient EGR Flow) or P2457 (EGR Cooler Performance)
- Bubbling or foaming in coolant degas bottle
- Loss of power under load (especially towing)
- White deposits around degas bottle cap
How to Fix
Replace EGR cooler (BC3Z-9V425-A for 2011-2016; HC3Z-9V425 for 2017+). For 2011-2012 trucks with DTC P0401 (Insufficient EGR Flow) and P2457 (EGR Cooler Performance), Ford TSB 13-6-5 applies; coverage follows the truck's normal warranty, so have a Ford dealer check the VIN. Preventive: use a fuel additive (Diesel Kleen, Hot Shots Secret EDT) to reduce soot. Perform regular EGR cleaning at 60,000-mile intervals. Upgrade kits from Sinister Diesel and Dorman (904-405 kit) include both EGR cooler and gaskets.
Sources for this issue (2)
Land Rover Discovery · 2010–2018
The EGR cooler on the 3.0L TDV6 and SDV6 diesel engines develops internal cracks that allow coolant to leak into the exhaust system. This causes white smoke from the exhaust, gradual coolant loss, and can contaminate the DPF. In the worst case, coolant enters the combustion chambers and causes hydrolock. This is considered one of the most serious diesel Discovery failures.
Common Symptoms
- White smoke from exhaust
- Gradual coolant loss with no external leak
- Sweet smell from exhaust
- Rough running or misfires
- Overheating
- Milky residue in coolant overflow
How to Fix
Replace the EGR cooler with the updated JLR design. Flush the cooling system and check for coolant contamination in the intake and exhaust. Inspect the DPF for coolant damage. Some owners delete the EGR system entirely (off-road use only). Budget for 8-12 hours labor.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- LR018752 genuine left EGR valve and cooler assemblyOEMLR018752.LRC
Replace a pressure-test-confirmed failed left EGR cooler/valve assembly on the matching 3.0 diesel branch Fitment/availability: Left-hand 3.0 TDV6 Discovery 4/5 listing, 2009-2019 family. Confirm VIN, engine generation and supersession; …
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- WarningMonitor coolant level weekly on TDV6/SDV6 models. Any unexplained coolant loss should be investigated immediately — EGR cooler failure can destroy the engine.
Audi A3 · 2010–2015
The EGR (Exhaust Gas Recirculation) valve and cooler can fail from carbon buildup, causing rough running, poor performance, and warning lights. OEM EGR valve: 03L131501K (Pierburg, supersedes 03L131501G). OEM EGR cooler: 03L131512AF (Genuine Audi). EGR cooler valve: 03L131501F. EGR pipe to cooler: 03G131547H. EGR cooler temperature sensor: 03L906529A. EGR vacuum solenoid (N239/N345): 1K0906283A. EGR to intake manifold O-ring seal: 03G131547C.
Common Symptoms
- Rough idle
- Loss of power
- Check engine light
- Black smoke from exhaust
- Poor throttle response
- Coolant loss (EGR cooler leak)
How to Fix
Clean or replace EGR valve (03L131501K). Inspect EGR cooler (03L131512AF) for leaks - coolant loss can indicate internal cooler failure. Regular intake cleaning helps prevent carbon buildup. Use quality diesel fuel. The EGR cooler removal process is documented at myturbodiesel.com for CBEA/CJAA engines.
Sources for this issue (1)
Chrysler Crossfire · 2004–2008
Mazda 626 · 1993–2000
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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 $50 to $5,000, depending on the vehicle and root cause.
Which vehicles are affected by P0402?
Au7o has documented P0402 across 34 vehicle models from 15 manufacturers: Audi, Chrysler, Ford, Jaguar, Jeep, Land Rover, Mazda, Mercedes-Benz, Opel, RAM, SEAT, Skoda, Toyota, Volkswagen, Volvo.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.