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P0401 is a diagnostic trouble code (DTC) for "Exhaust Gas Recirculation Flow Malfunction". 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.
Exhaust Gas Recirculation Flow Insufficient Detected
P0401 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) valve is not flowing enough recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.
The EGR valve is not opening all the way due to a low vacuum opening the valve from the EGR control solenoid or the EGR not being able to hold vacuum.
The EGR temperature sensor is not registering enough of a temperature change when the EGR valve is opened.
The EGR passages are partly blocked and will not allow enough flow of exhaust gases into the intake manifold.
Scans codes and documents the freeze frame data in order to verify the problem.
Clears the engine and ETC codes and road tests the vehicle to verify whether the codes come back.
Visually checks the vacuum hoses, wiring, and connections to the EGR valve and control solenoid along with the EGR temperature sensor.
Disconnects and checks the EGR valve is getting enough engine vacuum to the valve when the control solenoid opens on light-to-medium acceleration.
Checks for EGR temperature sensor changes and engine to bog down when the EGR is opened.
Removes EGR valve and temperature sensor to check for excessive carbon buildup or partial blockage of the EGR tubes from the valve to the intake manifold.
Failing to check and clean the EGR passages when replacing a defective EGR valve.
Condemning a good EGR valve when the EGR temperature sensor has excessive carbon buildup on it causing the failure code.
Failing to check to see if the EGR control solenoid will hold vacuum before replacing the EGR valve.
A failed EGR valve can cause the engine to have excessive ignition pre-ignition that can cause internal engine damage to the piston and valves.
The Check Engine Light on will cause the vehicle to fail emission testing from excessive NOx gases.
Replacing the leaking or clogged EGR valve
Replacing a broken vacuum line to the EGR valve or control solenoid
Replacing an EGR temperature sensor or clean the carbon off of it to repair it if it does not register enough of a temperature change
Cleaning carbon out of EGR tubes to intake manifold to clear any blockages
Code P0401 is triggered when the EGR temperature sensor does not see enough of a temperature change when the EGR is commanded to open. These sensors tend to get a lot of carbon buildup that causes them to lose sensitivity to the heat from the EGR gases.
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