Technical Definition:

Exhaust Gas Recirculation (EGR) Control Circuit Range / Performance

Technical Description:

The EGR (Exhaust Gas Recirculation) system’s purpose is to redirect exhaust gas back into the cylinders. Since exhaust gas is inert, it displaces oxygen and fuel, thereby lowering cylinder temps, which, in turn, lowers oxides of nitrogen emissions. 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. (Too much EGR and the engine won’t idle).

Possible Causes:

• Open or short in the 5 Volt reference circuit
• Open or short in the ground circuit
• Open or short in the PCM controlled voltage circuit
• Bad PCM (less likely)

Possible Symptoms:

There may be no symptoms of a P0404 obd code other than the MIL (malfunction indicator lamp) or check engine light. However, Exhaust Gas Recirculation systems are inherently problematic due to carbon buildup in the intake manifold, etc. This normal buildup can lodge in an EGR valve, holding it open when it should be closed. If this is the case, the engine 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 Nox emissions. But the latter symptoms aren’t going to be noticeable to a driver.

Exhaust Gas Recirculation Circuit Range/Performance

Possible Solutions:

• Using a scan tool command the EGR valve to open while watching the actual EGR position (it will probably be labeled “desired EGR” or something similar). The actual EGR position should be very close to the “desired” EGR position. If it is, then the problem is likely intermittent. It may have been a lodged piece of carbon that has since dislodged, or it could be a bad EGR valve winding that intermittently 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 the connector. If it doesn’t show a reference voltage, repair an open or short in the 5 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 should indicate 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 indicate voltage that varies according to the percentage that the EGR is open. As it’s open more, the voltage should increase accordingly. If it does, then replace the EGR valve.
• If the voltage doesn’t increase incrementally, then repair open or short in EGR control circuit.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– EGR volume control solenoid valve
– EGR volume control solenoid valve harness is open or shorted
– EGR volume control solenoid valve circuit poor electrical connection
– EGR temperature sensor and circuit

Specific Makes:

– Engine hesitation