P0404 Exhaust Gas Recirculation Circuit Range/Performance

Description and meaning of DTC p0404

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. The EGR (Exhaust Gas Recirculation) system's purpose is to redirect exhaust gasback into the cylinders. Since exhaust gas is inert, it displaces oxygen and fuel,thereby lowering cylinder temps, which, in turn, lowers oxides of nitrogenemissions. For that reason it needs to be carefully metered into the cylinders(via the EGR valve) so as not to adversely affect the engine's performance. (Toomuch EGR and the engine won't idle). If you have a P0404, then the EGR valve islikely an electrically controlled EGR valve instead of a vacuum controlled EGRvalve. Also, the valve will usually have a feedback system built into it thatinforms the PCM (Powertrain Control Module) what position the valve is in open,closed, or somewhere in between. The PCM needs to know this to determine whether ornot the valve is operating as needed. If the PCM determines that the valve should beoperating, but the feedback circuit shows that the valve is not open, this code willset. Or if the PCM determines the valve should be closed but the feedback signalindicates that the valve is open, this code will set.

p0404 diagnostic trouble code symptoms

There may be no symptoms of a P0404 DTC other than the MIL (malfunction indicator lamp) or checkengine light. However, Exhaust Gas Recirculation systems are inherently problematicdue to carbon buildup in the intake manifold, etc. This normal buildup can lodge inan EGR valve, holding it open when it should be closed. If this is the case, theengine may idle rough, or not at all. If the valve has failed and is NOT opening,then symptoms would be higher combustion temps and as a result, higher Noxemissions. But the latter symptoms aren't going to be noticeable to a driver.

DTC p0404 - possible causes

Usually this code points to either carbon buildup or a bad EGR valve. However thatdoesn't rule out the following: Open or short in the 5 Volt reference circuit Open or short in the ground circuitOpen or short in the PCM controlled voltage circuitBad PCM (less likely)

How to fix OBD-II diagnostic trouble code p0404

Using a scan tool command the EGR valve to open while watching the actual EGRposition (it will probably be labeled desired EGR or something similar). Theactual EGR position should be very close to the desired EGR position. If itis, then the problem is likely intermittent. It may have been a lodged piece ofcarbon that has since dislodged, or it could be a bad EGR valve winding thatintermittently opens or shorts as the valve temperature changes. If the EGR desired position is not close to the actual position,then unplug the EGR sensor. Check for a good 5 Volt reference voltage to theconnector. If it doesn't show a reference voltage, repair an open or short in the5 Volt reference circuit. If there is a 5 volt reference voltage, activate the EGR with the scanner,monitor the EGR ground circuit with a DVOM (Digital Volt/Ohm meter). It shouldindicate a good ground. If it doesn't then repair the ground circuit. If there is a good ground, then check the control circuit. It should indicatevoltage that varies according to the percentage that the EGR is open. As it'sopen more, the voltage should increase accordingly. If it does, then replace theEGR valve. If the voltage doesn't increase incrementally, then repair open or short inEGR control circuit. Related EGR codes: P0400, P0401, P0402, P0403, P0405, P0406, P0407, P0408, P0409

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