Description of DTC code P0404

The EGR (Exhaust Gas Recirculation) valve is used to reduce NOx (Nitrogen Oxides) emissions. To do this, it feeds small portions of exhaust gas into the combustion chamber. It is worth mentioning that NOx (Nitrogen Oxides) is caused by high temperature. High temperature is reduced when the air/fuel mixture is diluted with the exhaust gases.

The design of the EGR (Exhaust Gas Recirculation) valve allows exhaust gases to be accurately supplied to the engine without using the vacuum in the intake manifold. Exhaust flow into the intake manifold is distributed by the EGR valve through an orifice that controls the PCM (Powertrain Control Module).

If you have the DTC code P0404 OBD2 set, this means that the EGR valve is electrically controlled. This valve has a feedback process, which notifies the PCM (Powertrain Control Module) of the position of the EGR valve, i.e. whether it is open, closed, or perhaps somewhere in between. This data is required by the PCM, as this provides proof of the EGR valve's function.

In case the PCM decides that the valve must be running, but the feedback loop indicates that the valve is not open, (applies in the opposite direction as well) the fault code P0404 is set.

Symptoms of fault code P0404

  • The Check Engine light comes on.
  • There may be pre-ignition in the acceleration.
  • The engine can be run at no load.
  • If the EGR valve does not open, the combustion temperature will be higher.

Causes of OBD2 P0404

The factors leading to the establishment of the P0404 OBD II diagnostic code are

  • An amount of accumulated carbon.
  • 5-volt EGR (Exhaust Gas Recirculation) valve reference circuit may be shorted.
  • A short circuit to ground in the EGR (Exhaust Gas Recirculation) valve circuit.
  • The EGR valve is defective.

Possible solutions of the DTC code P0404

The steps to follow to repair the problems of code P0404 are:

  • By using the scanner of your choice, you must command the EGR valve to open, then observe the actual position. The actual position of the EGR valve should be close to the desired position. If it is, the problem is intermittent, perhaps because of some carbon element that has come off.
  • If the desired position is not close to the actual position, disconnect the EGR valve, and check that the reference voltage is present at the connector (5 volts). If not, a short in the reference circuit is indicated, proceed to repair it.
  • If the reference voltage is present, activate the EGR valve with the scanner, monitor the ground circuit with the help of a digital multimeter. The result should be a good ground. If not, repair the ground circuit.
  • If there is no problem in the ground circuit, check the control circuit. The voltage should vary according to the function of the EGR valve. That is, the more open the EGR valve is, the higher the voltage should be. If so, the problem is in the EGR valve. Change it.
  • If the control circuit voltage does not change according to the EGR valve, this indicates a problem in the circuit. Repair it.

Codes related to P0404

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