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P0400 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 Malfunction
P0400 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) valve is not flowing recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.
The EGR valve is not opening due to no vacuum opening the valve from the EGR control solenoid or the EGR not holding vacuum.
The EGR temperature sensor is not registering a temperature change when the EGR valve is opened.
The EGR passages are blocked and will not allow 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 car to verify whether the code comes 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 vacuum to the valve when the control solenoid opens on light to medium acceleration.
Checks for EGR temperature sensor change and engine to bog down when the EGR is opened.
Removes EGR valve and temperature sensor to check for excessive carbon buildup or blockage of EGR tubes.
Replacing the EGR valve before checking for carbon build up on the EGR temperature sensor.
Replacing the EGR valve without checking the EGR pressure transducer for proper function.
A failed EGR valve can cause the engine to have excessive 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.
Code P0400 is triggered when the EGR temperature sensor does not see 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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