OBD-II Code P0402 — What It Means & How to Fix It

What Does This Error Mean?

P0402 means the EGR (Exhaust Gas Recirculation) system is flowing more exhaust gas than expected. The EGR system recirculates a small amount of exhaust back into the intake to reduce emissions. Too much EGR flow causes a rough idle, stalling, and hesitation. The most common cause is an EGR valve stuck in the open position.

Affected Models

All vehicles 1996+
Common in Toyota Camry, Corolla, and Tacoma
Common in Honda Civic and Accord
Common in Ford Focus and Escape
Common in Chevrolet Silverado and Colorado

Common Causes

EGR valve stuck open and flowing exhaust gas constantly
Stuck EGR position sensor reporting incorrect valve position
Carbon buildup holding the EGR valve slightly open
Vacuum leak in the EGR control line keeping the valve open
Faulty EGR control solenoid not properly regulating flow

How to Fix It

Locate the EGR valve on your engine. It's typically a round or rectangular metal valve bolted to the intake manifold with a vacuum or electrical connector. On many vehicles it's clearly visible from above.

EGR valves are often covered in carbon soot after years of use — this is normal and expected.
Remove the EGR valve and inspect it. Look for carbon buildup keeping the valve plate from closing fully. Use EGR cleaner spray and a small brush to clean the valve seat and disc thoroughly.

Soak the valve in EGR cleaner for 15-30 minutes if the carbon is heavy. Avoid getting cleaner on rubber components or electrical connectors.
With the valve removed, clean the EGR passage in the intake manifold as well. Carbon often builds up inside the passage and can restrict or affect flow even after the valve is cleaned.

A pick tool and throttle body cleaner work well for cleaning the intake manifold passage.
If the EGR valve has an electronic position sensor, test the sensor output with a multimeter or scan tool while manually moving the valve. Compare readings to spec. A stuck or erratic sensor can cause a false P0402 reading.

On many modern vehicles, the EGR valve and position sensor are an integrated assembly — replace as a unit if the sensor is faulty.
Check the EGR vacuum line (on vacuum-operated valves) for cracks, kinks, or disconnection. A cracked vacuum line can hold the valve open. On electronic EGR systems, inspect the solenoid connector and test solenoid resistance.

EGR solenoid resistance is typically 20-70 ohms — check your service manual for the exact specification.

When to Call a Professional

If cleaning the EGR valve doesn't help, have a mechanic test the valve and solenoid electrically. A technician can command the EGR valve open and closed using a scan tool to verify operation. This quickly identifies a stuck valve vs. a sensor or solenoid problem. Diagnosis typically costs $80-$130. EGR valve replacement typically runs $150-$400 depending on vehicle.

Frequently Asked Questions

Why does too much EGR flow cause a rough idle?

Exhaust gas doesn't burn — it's already been through combustion. At idle, the engine needs a precise air-fuel mixture. If too much exhaust gas enters the intake, it dilutes the mixture. The cylinders don't get enough fresh air and fuel to combust properly. This causes a rough, stumbling idle or even stalling.

Can I just delete the EGR system to fix P0402?

Not legally on road-registered vehicles in most countries. Deleting or disabling emissions equipment is illegal and will cause a permanent check engine light. It will also cause automatic failure of emissions testing. The proper fix is cleaning or replacing the EGR valve.

Will P0402 get worse over time if ignored?

It can. A stuck-open EGR valve that can't be cleaned will continue to cause rough idle and stalling. Over time, excess exhaust gas can also cause carbon buildup in the intake manifold. Clean or replace the valve and you'll likely see improved performance and fuel economy.