P0402 OBD-II Trouble Code: Exhaust Gas Recirculation Flow Excessive Detected

P0402 code definition

Exhaust Gas Recirculation Flow Excessive Detected

What the P0402 code means

P0402 is an OBD-II generic code that the engine control module (ECM) has detected indicating the engine exhaust gas recirculation (EGR) valve is flowing too much recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.

What causes the P0402 code?

  • The EGR valve is opening all the way or more than needed due to a blocked vacuum diaphragm in the EGR vacuum back pressure valve.

  • The EGR temperature sensor is registering too much of a temperature change when the EGR valve is opened from a partly blocked exhaust catalyst causing excessive back pressure in the EGR system.

  • The EGR is stuck open due to binding or carbon deposits holding the valve open.

What are the symptoms of the P0402 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.
  • The engine could be running rough if the valve is stuck open.
  • The engine EGR system may have exhaust leaks at the back pressure transducer.

How does a mechanic diagnose the P0402 code?

  • Scans codes and documents the freeze frame data in order to verify the problem.

  • Clears the engine and ETC codes and road tests to verify that the code comes back.

  • Visually checks the vacuum hoses, wiring, connections to the EGR valve, and control solenoid, along with the EGR temperature sensor and back pressure transducer.

  • Disconnects and checks to see if the EGR valve vacuum can be controlled to the valve when the control solenoid opens on light-to-medium acceleration and not just when it is open fully.

  • Checks the exhaust catalyst for damage or excessive back pressure on the EGR system.

  • Removes EGR valve and temperature sensor to check for carbon holding the EGR valve open or the EGR bleed port not being blocked with carbon not allowing the valve to bleed off vacuum.

Common mistakes when diagnosing the P0402 code

  • Replacing the EGR valve without checking the EGR pressure transducer to see if it can control the EGR valve opening.

  • Not checking to see if the EGR valve is being held open mechanically by a piece of carbon before replacing it.

How serious is the P0402 code?

  • An EGR that has excessive flow can cause the engine to hesitate or stall on acceleration or have a very rough engine idle.

  • The Check Engine Light on will cause the vehicle to fail emission testing.

  • If the catalyst is blocked causing code, then it could cause engine to lose power or not start.

What repairs can fix the P0402 code?

  • Replacing the stuck open EGR valve

  • Replacing a broken catalyst in the exhaust

  • Replacing an EGR temperature sensor or cleaning the carbon off of it to repair it if it registers too much of a temperature change

  • Replacing the EGR backpressure control valve

Additional comments for consideration regarding the P0402 code

Code P0402 is triggered when the EGR temperature sensor sees more of a temperature change than the EGR has commanded to open. This is usually caused by the EGR backpressure control valve getting a burnt diaphragm from the exhaust backpressure over time or from a partly blocked catalyst.

Need help with a P0402 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

More related articles

P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222 code means The manufacturer specifies a range of acceptable voltage to be produced from the throttle position...
Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...

Related questions

Q: The car with the sensor reference, low circuit and ceased voltage doesn't start

The first thing you want to do is have a certified mechanic unplug the main computer and test the wires coming out of it. Either the wiring is bad, or the computer's connectors have a little condensation and corrosion, which...

Q: After 'check engine' light, diagnostic revealed P0171 and P0402

The first code, P0171, is an indication the engine is running lean. This code can indicate anything from clogged air and fuel filters to problems with O2 sensors and mass air flow sensors to intake gaskets. The other code,...

Q: Getting random misfire code.

Your Chrysler sets a P0300 random or multiple misfire code when more than a 1.8% misfire rate is measured during two trips. Countless issues can set this code, from a vacuum leak to a bad coil pack. Your engine is...