P0402 is an OBD-II trouble code that means your engine computer has detected “excessive EGR flow.” In plain English, the exhaust gas recirculation (EGR) system is letting too much exhaust back into the intake. That can cause rough running, poor fuel economy, and sometimes a check engine light with other codes. You’ll often see this on higher-mileage vehicles or engines that do a lot of short-trip city driving. The fix can be simple, but if you ignore it, you risk drivability issues and potential damage to other components.
What Does P0402 Mean?
P0402 stands for “Exhaust Gas Recirculation Flow Excessive Detected.” The ECU commands a certain amount of EGR flow and then monitors sensors (MAP, MAF, EGR position, O2 sensors) to confirm that flow. When the ECU sees more EGR flow than expected for a given condition, it sets P0402.
This usually points to an EGR valve that’s stuck open, carbon buildup holding the valve off its seat, or a control issue that’s allowing the valve to open when it shouldn’t. On some newer engines with electronic EGR, it can also be a sensor or wiring problem.
Quick Reference
- Code: P0402 – EGR Flow Excessive Detected
- System: Exhaust Gas Recirculation (EGR)
- Severity: Moderate – can affect drivability and emissions
- Common Causes: Stuck EGR valve, carbon buildup, faulty EGR control solenoid
- Typical Repairs: Clean or replace EGR valve, repair vacuum/hoses, update or reflash ECU
Real-World Example / Field Notes
In the shop, I see P0402 a lot on higher-mileage trucks and sedans that spend their life in traffic. A common scenario: customer complains of rough idle, poor fuel economy, and a check engine light. Scan tool shows P0402, sometimes with a misfire code. Pull the EGR valve and it’s caked with carbon, or the pintle is stuck slightly open. After cleaning the EGR passages, verifying vacuum or command from the ECU, and clearing the code, the engine usually idles smooth again and fuel economy improves.
Symptoms of P0402
- Check engine light on: P0402 usually sets the MIL and may be stored as a confirmed or pending code.
- Rough idle: Too much EGR at idle can cause stumbling, shaking, or even stalling at stoplights.
- Hesitation or stumble: You may feel a flat spot or hesitation during light acceleration or cruising.
- Poor fuel economy: Excessive EGR flow can hurt combustion efficiency and reduce MPG.
- Loss of power: The engine may feel weak, especially at low RPM or under light load.
- Hard starting: In severe cases, a stuck-open EGR valve can make the engine hard to start.
- Other codes present: You might see related EGR, MAP/MAF, or misfire codes stored with P0402.
Common Causes of P0402
Most Common Causes
- Stuck-open EGR valve: Mechanical or electronic EGR valves can stick due to wear or carbon, allowing constant flow.
- Carbon buildup in EGR passages: Heavy deposits in the intake or EGR channels can hold the valve off its seat or redirect flow.
- Faulty EGR control solenoid or valve driver: On vacuum-operated systems, a bad solenoid can apply vacuum when it shouldn’t.
- Incorrect EGR valve installation: Aftermarket or mis-installed valves can flow more than the ECU expects.
- ECU calibration issues: Some vehicles need an ECU reflash because factory calibration is too sensitive to EGR flow.
Less Common Causes
- Faulty DPFE or EGR flow sensor: On Ford and some other makes, a bad DPFE sensor can falsely report high EGR flow.
- Wiring or connector problems: Shorted wiring to the EGR valve or sensor can cause incorrect command or feedback.
- MAP/MAF sensor errors: If these sensors are skewed, the ECU may believe EGR flow is higher than it really is.
- Exhaust leaks near EGR feed: Rare, but leaks can change pressure readings and confuse EGR flow calculations.
- Intake manifold issues: Cracks or modifications that alter airflow can cause the ECU to misinterpret EGR behavior.
Diagnosis: Step-by-Step Guide
You’ll want a basic OBD-II scan tool (ideally with live data and Mode $06), a hand vacuum pump (for vacuum-operated EGR), a multimeter, and basic hand tools. Access to a service manual or reliable repair data is also very helpful for pinouts and specifications.
- Confirm the code: Scan the vehicle and verify P0402 is present. Check for additional EGR, MAP/MAF, or misfire codes that can guide you.
- Check freeze frame data: Look at RPM, load, speed, and temperature when P0402 set. This tells you if it happens at idle, cruise, or acceleration.
- Perform a visual inspection: Inspect the EGR valve, vacuum lines, electrical connectors, and wiring harness for cracks, loose plugs, or obvious damage.
- Test EGR valve operation: On vacuum EGR, apply vacuum with a hand pump at idle. The engine should stumble or stall; if it’s already rough with no change, the valve may be stuck open. On electronic EGR, use a scan tool bi-directional control to command the valve and watch RPM and sensor changes.
- Check EGR position or DPFE sensor data: Monitor EGR position or DPFE voltage on the scan tool. Compare to factory specs. A sensor that reads high flow when the valve is commanded closed can trigger P0402.
- Inspect and clean EGR passages: Remove the EGR valve and inspect the ports in the intake and exhaust. Clean out carbon with appropriate tools and cleaner, making sure not to drop debris into the engine.
- Verify vacuum and control signals: On vacuum systems, check for proper vacuum supply and that the control solenoid is not leaking or stuck. On electronic systems, use a multimeter to verify power, ground, and command signal at the EGR connector.
- Check related sensors: Look at MAP/MAF readings before and after commanding EGR. If readings are unrealistic or don’t change, you may have a sensor issue instead of actual excessive flow.
- Review Mode $06 data: Some scan tools let you see EGR monitor test results. This can show borderline EGR performance before the code resets.
- Clear codes and road test: After repairs or cleaning, clear the codes and perform a drive cycle under similar conditions to confirm P0402 does not return.
Pro tip: Don’t just throw an EGR valve at it. On many vehicles, cleaning the valve and passages plus checking the EGR control solenoid or DPFE sensor solves P0402 without expensive parts.
Possible Fixes & Repair Costs
The correct fix depends on what you find during diagnosis. Common repairs include cleaning or replacing the EGR valve, cleaning clogged EGR passages in the intake, replacing a faulty EGR control solenoid or DPFE sensor, repairing vacuum lines, or updating ECU software. Typical repair costs at a shop range from about $120–$250 for cleaning and basic vacuum/solenoid repairs, up to $250–$600 for EGR valve or sensor replacement. Costs vary with vehicle make, engine layout, part quality (OEM vs aftermarket), and local labor rates.
Can I Still Drive With P0402?
In most cases, you can still drive with P0402 without immediate catastrophic damage, but the car may not run well. You might notice rough idle, hesitation, and poor fuel economy. Extended driving with excessive EGR flow can foul spark plugs, stress the catalytic converter, and make the vehicle fail an emissions test. If the engine starts to stall, misfire badly, or lose power, you should avoid driving and have it checked as soon as possible.
What Happens If You Ignore P0402?
If you ignore P0402, the engine will continue to run with incorrect EGR flow, which can lead to long-term carbon buildup, misfires, and potential damage to the catalytic converter. Fuel economy will suffer, drivability can worsen over time, and you’ll almost certainly fail any emissions inspection until the issue is repaired.
Related Codes
- P0474 – Exhaust Pressure Sensor Intermittent
- P0473 – Exhaust Pressure Sensor High
- P0472 – Exhaust Pressure Sensor Low
- P0471 – Exhaust Pressure Sensor Range/Performance
- P0470 – Exhaust Pressure Sensor
- P0469 – EVAP Purge Flow Sensor Circuit Intermittent
- P0468 – EVAP Purge Flow Sensor Circuit High
- P0467 – EVAP Purge Flow Sensor Circuit Low
- P0466 – EVAP Purge Flow Sensor Circuit Range/Performance
- P0465 – EVAP Purge Flow Sensor Circuit
Key Takeaways
- P0402 means the ECU detects excessive EGR flow, usually from a stuck EGR valve or carbon buildup.
- Common symptoms include a check engine light, rough idle, hesitation, and poor fuel economy.
- Proper diagnosis involves checking the EGR valve, passages, control solenoid, and related sensors like DPFE, MAP, and MAF.
- Repairs often involve cleaning or replacing the EGR valve and passages, with typical shop costs in the low to mid hundreds.
- You can usually drive short-term with P0402, but ignoring it can lead to bigger drivability and emissions problems.
Vehicles Commonly Affected by P0402
P0402 shows up across many makes, but some patterns are common in the field. Ford cars and trucks (especially older models with DPFE sensors), GM vehicles (Chevy, GMC, Buick) with vacuum-operated or electronic EGR valves, and many Chrysler/Dodge/Jeep models are frequent visitors. It’s also seen on some Toyota, Honda, Nissan, and Hyundai engines that build up carbon in the intake. High-mileage SUVs, pickups, and city-driven sedans tend to experience P0402 more often due to heat cycles and carbon accumulation.
FAQ
Can P0402 cause misfires?
Yes. If the EGR valve is stuck open or flowing too much at idle or low RPM, it can dilute the air-fuel mixture and cause random or cylinder-specific misfires. You might see misfire codes (P0300–P030X) stored along with P0402.
Is P0402 serious enough to fix right away?
It’s not usually an emergency like a low oil pressure issue, but you shouldn’t ignore it. Excessive EGR flow affects drivability, fuel economy, and emissions. Fixing it sooner prevents carbon buildup, plug fouling, and potential catalytic converter damage.
Can cleaning the EGR valve fix P0402?
Often, yes. If the EGR valve and passages are carboned up but the valve and sensors are otherwise good, a thorough cleaning can restore normal flow and clear P0402. However, if the valve is worn, the solenoid is faulty, or the sensor is inaccurate, you may still need parts replacement.
How do I know if my EGR valve is stuck open?
Common signs include rough idle, stalling at stoplights, poor low-speed power, and sometimes hard starting. With a scan tool or vacuum pump, you can test the valve: if the engine runs poorly even when the valve should be fully closed, it may be stuck open.
Can a bad MAP or MAF sensor trigger P0402?
Yes. The ECU uses MAP and/or MAF readings to calculate EGR flow. If those sensors are skewed, the ECU might think there is more EGR flow than there really is and set P0402. That’s why checking sensor data is an important part of diagnosis, not just the EGR valve itself.