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

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Cost of diagnosing the P0402 code

P0402 is a diagnostic trouble code (DTC) for "Exhaust Gas Recirculation Flow Excessive Detected". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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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?

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