# P0402: Exhaust Gas Recirculation "A" Flow Excessive Detected **Verdict:** Drive to a shop this week Emissions - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$750 - **Urgency:** This week - **Most likely:** EGR valve stuck open - **DIY?:** Steps 1-2 ## Quick answer P0402 means the engine computer has measured more exhaust gas recirculation (EGR) flow than it asked for, often when it wanted none at all. Exhaust entering the engine at idle dilutes the air and fuel mix, so the engine can idle rough, hesitate, or stall. A valve stuck open from carbon is the usual cause. ## What does P0402 mean? The EGR valve lets a controlled amount of exhaust back into the intake to cool combustion and reduce nitrogen oxides. It is meant to stay closed at idle, during cold running, and at full throttle, because the engine needs mostly fresh air at those times. Exhaust is already burned gas, so any exhaust in the cylinder takes the place of oxygen the engine could have used to burn fuel. P0402 sets when the computer sees more EGR flow than it commanded, often flow when the valve should be shut. It may detect this from a valve-position sensor that reads open, a flow or pressure sensor that reads high, or an intake pressure and fuel-mixture pattern that only makes sense with exhaust leaking in. On most cars the fault has to show up on two drive cycles before the light comes on. "A" means the first or only EGR system. Unlike P0401, this code often changes how the car idles. ## What are the symptoms of P0402? - Rough or shaky idle - Engine stalls when coming to a stop - Hesitation when pulling away - Check engine light on ## What causes P0402? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **EGR valve stuck open** (most common). Carbon flakes can break loose and wedge between the valve and its seat, holding it partly open so exhaust flows all the time. It is most common on high-mileage engines and on those that burn oil. A strong clue is that idle quality improves when the valve is unplugged, vacuum-capped, or blocked off as a test. 2. **Faulty EGR pressure or position sensor** (common). A failed position or pressure sensor can report high flow when the valve is actually closed. On pressure-sensor systems, swapping the two sensor hoses during a repair, or a cracked hose, can produce the same false reading. If the engine idles smoothly but the code keeps returning, a faulty reading is more likely than real excess flow. 3. **EGR control solenoid stuck on** (less common). On vacuum-operated systems, a control solenoid decides when vacuum reaches the valve. If the solenoid sticks open or a hose bypasses it, vacuum stays applied and the valve stays open at idle. This mainly affects older vehicles. Pulling the vacuum hose off the valve at idle and capping it is a quick way to check. 4. **Wiring short in the EGR control circuit** (rare). A wire that chafes through and touches ground or power can hold an electronic EGR valve or solenoid on even when the computer commands it off. EGR wiring runs close to hot exhaust parts, so melted insulation is the usual reason. This is rare, and circuit codes such as P0403 often appear alongside P0402 when it happens. ## How do you diagnose P0402? 1. Check freeze-frame data, then watch EGR position or flow data at idle, where it should show closed. 2. Inspect sensor hoses for correct routing and cracks. 3. Unplug or vacuum-cap the EGR valve at idle. A big improvement in idle means the valve or its control is at fault. 4. Remove the valve and look for carbon holding it open. ## How do you fix P0402, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Clean or replace EGR valve | $150-$750 | Cleaning can work if carbon is the only problem. A worn seat or failed motor needs a new valve. | | Replace EGR flow or position sensor | $100-$300 | Fixes false high readings. | | Replace EGR control solenoid | $100-$250 | Applies to vacuum-controlled systems. | ## Is it safe to drive with P0402? > **Drive to a shop this week.** The car is usually drivable, but stalling at stops or in traffic is a safety risk. Get it repaired soon if the engine stalls or hesitates. ## Will P0402 fail an emissions test? A stored P0402 with the check engine light on will fail an OBD-based emissions test in most states. Excess EGR does not usually raise NOx, but rough running can raise hydrocarbon readings on tailpipe tests. If you clear the code just before testing, the EGR monitor will read not ready, and the car may be turned away. ## After the repair: clearing P0402 After cleaning or replacing the valve or sensor, clear the code and check that the idle is smooth right away, since a stuck-open valve is usually obvious at idle. Then drive normally for several days. The fix is confirmed when the EGR monitor completes, no pending code returns, and stalling or stumbling at stops has ended. ## How to prevent P0402 - Drive at highway speeds regularly so carbon does not build up as loose flakes that can jam the valve. - Fix oil consumption early, since oily soot is stickier and more likely to hold a valve off its seat. - Check that EGR sensor hoses go back on the correct ports after any work near the valve. - Keep the EGR connector and wiring clear of exhaust heat when other work is done nearby. - Do not ignore a new rough idle, because a partly stuck valve can worsen and start stalling the engine. ## Codes often seen with P0402 - [P0400](/codes/p0400): Exhaust Gas Recirculation "A" Flow - [P0401](/codes/p0401): Exhaust Gas Recirculation "A" Flow Insufficient Detected - [P0403](/codes/p0403): Exhaust Gas Recirculation "A" Control Circuit - [P0505](/codes/p0505): Idle Air Control System - [P0506](/codes/p0506): Idle Air Control System RPM Lower Than Expected ## Frequently asked questions ### Can I drive with a P0402 code? You can drive short distances with P0402 if the engine is not stalling. A stuck-open EGR valve can stall the engine at stoplights or while turning into traffic, which is a real safety risk. Repair it soon, and avoid heavy traffic if the idle is shaky or the engine dies when you stop. ### Why does a stuck EGR valve cause stalling? At idle the engine needs almost all fresh air, not burned exhaust. When exhaust leaks in through a stuck valve, it crowds out oxygen and slows combustion, so the engine stumbles or dies. At higher speeds the engine can tolerate more EGR, which is why the car may drive fine once it is moving. ### Can I just unplug the EGR valve? Unplugging the EGR valve is a useful test, but not a fix. If the valve is mechanically stuck open, unplugging it will not close it, and on most cars it sets more codes and keeps the light on. Leaving it disabled can also lead to pinging and a failed emissions test. ### How much does it cost to fix P0402? Most P0402 repairs cost $100 to $750 at an independent shop. Replacing a flow sensor, position sensor, or vacuum solenoid usually runs $100 to $300. Cleaning or replacing the EGR valve costs $150 to $750, depending on whether the valve is electronic and how much has to come off to reach it. ### Will P0402 make me fail an emissions test? Yes, a car with P0402 stored will fail an OBD-based emissions test in most states. A rough idle from excess EGR can also raise hydrocarbon readings on tailpipe tests. Clearing the code just before the test resets the readiness monitors, so repair the cause first and let the monitors complete. ### Can I fix P0402 myself? You can often handle the first steps yourself. Remove the valve, look for carbon holding it open, and clean it with throttle body cleaner and a plastic scraper. If the seat is worn, the motor has failed, or the sensor data needs a scan tool to interpret, a shop is the better choice. ### What are the symptoms of too much EGR flow? The most common signs of too much EGR flow are a rough or shaky idle, stalling when coming to a stop, and hesitation when pulling away. Symptoms are often worst with a warm engine at idle and may fade at cruising speed. The check engine light usually follows after two drive cycles. ### Can P0402 cause idle or misfire codes? Yes, excess EGR flow can upset the idle enough that the computer also sets idle control codes such as P0505 or P0506, or even misfire codes. Fix the EGR problem first, then clear all codes and see which ones return. The idle codes often stay away once exhaust stops leaking in. ### Will cleaning the EGR valve fix P0402? Cleaning often fixes P0402 if carbon is the only thing holding the valve open. If the valve seat is worn or pitted, the pintle is bent, or the electronic motor is failing, the valve will keep leaking and needs replacing. Retest the idle after cleaning to see whether the problem is really gone. ### What is the difference between P0401 and P0402? P0401 means the computer saw too little EGR flow, while P0402 means it saw too much. Too little flow usually causes pinging and high NOx, while too much causes a rough idle and stalling. Both can come from carbon, but in opposite ways, with blocked passages versus a valve held open. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other emissions codes - [P0400 Exhaust Gas Recirculation "A" Flow](https://diagxcar.com/codes/p0400) - [P0401 Exhaust Gas Recirculation "A" Flow Insufficient Detected](https://diagxcar.com/codes/p0401) - [P0403 Exhaust Gas Recirculation "A" Control Circuit](https://diagxcar.com/codes/p0403) - [P0404 Exhaust Gas Recirculation "A" Control Circuit Range/Performance](https://diagxcar.com/codes/p0404) - [P0405 Exhaust Gas Recirculation Sensor "A" Circuit Low](https://diagxcar.com/codes/p0405) - [P0406 Exhaust Gas Recirculation Sensor "A" Circuit High](https://diagxcar.com/codes/p0406) - [P0410 Secondary Air Injection System "A"](https://diagxcar.com/codes/p0410) - [P0411 Secondary Air Injection System "A" Incorrect Flow Detected](https://diagxcar.com/codes/p0411) - [P0420 Catalyst System Efficiency Below Threshold (Bank 1)](https://diagxcar.com/codes/p0420) - [P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)](https://diagxcar.com/codes/p0421) ## Symptoms - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) ## Repair costs - [EGR valve replacement cost](https://diagxcar.com/cost/egr-valve-replacement) ## Terms explained - [What is EGR valve?](https://diagxcar.com/glossary/egr-valve) --- Source page: https://diagxcar.com/codes/p0402 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.