P0402 Excessive Exhaust Gas Recirculation Flow Detected

P0402 - Technical Description

Excessive exhaust gas recirculation (EGR) flow detected.

P0402 is a generic OBD-II code detected by the engine control module (ECM) indicating that the engine exhaust gas recirculation (EGR) valve is allowing too much recirculated exhaust gas when commanded to open the intake manifold gas flow.

What does trouble code P0402 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle exhaust system and is used to reduce combustion temperature and pressure in order to control nitrogen oxides.

Typically, an exhaust gas recirculation system consists of three parts: an exhaust gas recirculation valve, an actuator solenoid and a differential pressure sensor (DPF). These things work together to provide the correct amount of recirculation based on engine temperature, load, etc. A P0402 code means that the OBD has detected an excessive amount of EGR.

Symptoms

You may notice problems with handling, for example, the engine may fail when idling. There may be other symptoms as well.

• The Check Engine light will come on and the code will be stored in the ECM.
• The engine may run rough if the valve is stuck in the open position.
• The engine's EGR system may have exhaust leaks at the backpressure sensor.

Causes of the P0402 code

The P0402 code most likely means that one or more of the following events have occurred:

• The DPFE (Differential Pressure) sensor is defective and needs to be replaced.
• Exhaust gas recirculation clogged (most likely carbon build-up).
• Exhaust gas recirculation valve defective
• The exhaust gas recirculation valve may not open due to lack of vacuum.

Possible solutions

In the case of P0402, people usually replace the EGR valve, but the problem comes back. The most likely solution is to replace the DPFE sensor.

• Check the voltage at the DPFE sensor at both idle and open EGR.
• Replace DPFE sensor.

Associated EGR Codes: P0400, P0401, P0403, P0404, P0405, P0406, P0407, P0408, P0409

HOW DOES A MECHANIC DIAGNOSTIC CODE P0402?

• Scans data freeze frame codes and documents to confirm the problem.
• Clears engine and ETC codes and road tests to see if the code returns.
• Visually inspect the vacuum hoses, wiring, connections to the EGR valve and control solenoid, and the EGR temperature sensor and back pressure sensor.
• Disables and tests if EGR valve vacuum can be applied to the valve when the control solenoid opens on light to moderate acceleration, not just full open.
• Checks the catalytic converter for damage or excessive back pressure in the EGR system.
• Removes the EGR valve and temperature sensor to check if the carbon is holding the EGR valve open and if the EGR purge port is blocked by the carbon preventing the valve from blowing out of the vacuum.

COMMON ERRORS WHEN DIAGNOSING CODE P0402

• Replace the EGR valve without checking the EGR pressure sensor to make sure it can control the opening of the EGR valve.
• Do not check if the EGR valve is held by a mechanically open piece of coal before replacing it.

HOW SERIOUS CODE P0402 IS?

• Excess gas recirculation with excessive flow can cause the engine to wobble or stall on acceleration, or cause the engine to idle very rough.
• An activated Check Engine light will cause the vehicle to fail the emissions test.
• If the catalytic converter is blocked causing the code, it could result in a loss of power or engine starting.

WHAT REPAIRS CAN FIX CODE P0402?

• Replacing a stuck open EGR valve
• Replacing a broken catalytic converter
• Replacing the EGR temperature sensor or cleaning it from carbon deposits to fix it if it registers too much temperature change.
• EGR Back Pressure Control Valve Replacement

ADDITIONAL COMMENTS TO BE AWARE OF CODE P0402

Code P0402 is triggered when the EGR temperature sensor detects a larger change in temperature than the EGR commanded to open. This is usually caused by the EGR backpressure control valve diaphragm being blown over time by exhaust backpressure or a partially blocked catalyst.

How to Fix P0402 Engine Code in 3 Minutes [2 DIY Methods / Only $4.26]

Need more help with your p0402 code?

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