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P0402 means too much exhaust gas is recirculating into the intake. A stuck-open EGR valve dilutes the air/fuel mixture at idle, causing rough running, stumbling, and sometimes stalling. Ford vehicles with vacuum-operated EGR and DPFE sensors are especially prone to this code. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0402 EGR valve stuck open, routing excess exhaust gas into the intake manifold
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0402 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
55%
#1 - Most Likely
EGR Valve Stuck Open
Carbon deposits or a failed solenoid hold the EGR valve partially or fully open when it should be closed at idle and light throttle. The result is rough idle, stalling, and hesitation. On Ford 5.4L and 4.6L engines, this is extremely common due to the vacuum-operated EGR design. Inspect for carbon buildup before replacing the valve.
🔩 Part
$40–$200
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
25%
#2 - Check First
Clogged EGR Differential Pressure (DPFE) Sensor
On Ford vehicles, the DPFE sensor measures EGR flow by monitoring pressure differential across an orifice. Carbon deposits in the sensor hoses or the sensor itself cause false-high flow readings, triggering P0402 even with a properly functioning EGR valve. Replace the DPFE sensor and clear its hoses.
🔩 Part
$30–$80
👨🔧 Labor
$40–$80
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Carbon Buildup Holding EGR Open
Heavy carbon accumulation on the EGR valve seat prevents it from fully closing. The valve itself may be electrically functional but physically jammed open by carbon. Cleaning with carb cleaner or EGR cleaner may resolve this without replacement - but severe buildup requires valve replacement.
🔩 Part
$5–$20
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
8%
#4 -
Faulty DPFE Sensor
A failed DPFE sensor outputs an incorrect voltage indicating excessive flow even when the EGR valve is closed. This is common on Ford 4.6L and 5.4L engines - it's often the first thing to replace when P0402 appears on these vehicles. The sensor typically costs under $50 and is easy to access.
🔩 Part
$25–$80
👨🔧 Labor
$40–$80
⚡ DIY Difficulty
Easy
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Inspect EGR Valve and Passages - Remove the EGR valve and inspect the valve seat and passages for heavy carbon buildup. Try cleaning with EGR/carb cleaner spray. The valve pintle should move freely and seat completely when not energized.
- Check DPFE Sensor Hoses (Ford) - On Ford vehicles, disconnect the two small hoses from the DPFE sensor and blow them clear. Soot-clogged hoses cause false-high pressure readings. Replace the DPFE sensor if hoses are clear but code persists.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need