OBD codes / P0402
P0402
ModerateExhaust Gas Recirculation (EGR) Flow Excessive
P0402 is generally safe to drive with short-term, though the rough idle or stalling at stops can be annoying and occasionally inconvenient. It's low-risk mechanically. Try cleaning the EGR valve and passages before replacing parts — a stuck-open valve from carbon is the common cause.
What this code means
The EGR system routes a measured amount of exhaust back into the intake to lower combustion temperatures and emissions. P0402 means too MUCH is flowing — the opposite of P0401. The usual cause is an EGR valve stuck open, often from carbon holding it off its seat, or a faulty EGR position sensor reporting the wrong amount. Excess exhaust at idle dilutes the mixture, so the classic symptom is a rough idle or stalling at stops. A cleaning often fixes it.
Symptoms you might notice
- Rough idle or stalling, especially at stops
- Hesitation at low speed
- Check-engine light
- Failed emissions test
What it costs to fix
Typical range: $100–$500 · about ~0.5–2.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| EGR clean (labor-only) | $0–$20 | ~1–2.5 hrs |
| EGR valve | $50–$300 | ~0.5–1.5 hrs |
| EGR position sensor | $25–$100 | ~0.3–1 hrs |
Cleaning out the carbon that holds the valve open is the cheap, common fix and may be labor-only. A new valve is modest; the sensor is cheaper. Cost climbs only if the EGR is buried in the intake.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0402 for my exact vehicle →
How to fix P0402
Moderate — doable at home with common tools and patience
- Correlate the code with the symptom
Excessive EGR flow shows up as rough idle or stalling at stops, because exhaust is diluting the mixture when the valve should be shut. If your idle misbehaves and P0402 is present, the valve being held open is the working theory.
- Pull the valve and look at the seat
Remove the EGR valve and inspect the pintle and seat: a chunk of carbon wedged under the pintle holds the valve cracked open and is the classic cause. You can often see the debris directly.
- Clean the pintle, seat, and passages
Clean until the pintle seats fully and moves freely — work the pintle by hand (or with vacuum on vacuum-style valves) while flushing with cleaner. A valve that snaps closed cleanly usually ends the problem without any new parts.
- Check the position sensor's resting reading
With the engine off and the valve closed, the EGR position value on a scan tool should sit at its closed spec (often near zero percent). A sensor reporting the valve open when it's physically shut is lying to the computer and needs replacement.
- Replace the valve if it won't seal
A worn pintle or a torn diaphragm on vacuum-operated valves means the valve can no longer seat even when clean. At that point replacement is the fix — transfer no old carbon into the new installation and use a fresh gasket.
DIY or shop? Like its low-flow sibling, this code usually yields to DIY cleaning — the valve is typically two bolts away, and the fault is visible carbon holding it open. A multimeter or scan tool covers the position-sensor check. Consider a shop if the valve is buried under intake plumbing on your engine, or if the idle problem persists after a verified-clean, verified-closing valve, which suggests a subtler control issue worth professional data analysis.
Tools for the DIY steps: Basic socket and wrench set · Carb/EGR cleaner spray · Picks and wire brushes · OBD-II scan tool with live data · New EGR gasket · Hand-held vacuum pump (vacuum-operated valves)
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0402.
Frequently asked
Can I drive with P0402?
Usually yes, short-term — it mainly causes a rough idle or stalling at stops. It's not a major safety issue, so you can drive to get it cleaned or diagnosed; fix it before an emissions test.
What's the difference between P0401 and P0402?
Opposite problems: P0401 is too LITTLE EGR flow (often a clogged valve/passages), P0402 is too MUCH (often a valve stuck open). Both are frequently solved by cleaning, but they point in opposite directions.
Will cleaning fix P0402?
Often — carbon holding the EGR valve open is the most common cause, and a thorough cleaning frequently restores proper flow. If it returns quickly, the valve or position sensor may need replacing.
How much does it cost to fix P0402?
Frequently inexpensive — a clean may be labor-only, and a valve or sensor is modest. Cost only rises if the EGR is buried in the intake and takes real disassembly to reach.
Seeing P0402 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0402 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.