P0404 Exhaust Gas Recirculation Circuit Out of Range / Performance

DTC P0404 -OBD-II Datasheet

Exhaust Gas Recirculation "A" Range / Performance

What does trouble code P0404 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

An exhaust gas recirculation system is designed to redirect exhaust gases back to the cylinders. Since the exhaust gases are inert, they displace oxygen and fuel, thereby lowering the temperature in the cylinders, which in turn reduces nitrogen oxide emissions. For this reason, it must be carefully metered into the cylinders (via the exhaust gas recirculation valve) in order not to interfere with the operation of the engine. (Too much EGR and the engine won't idle).

If you have a P0404, the EGR valve is most likely an electrically controlled EGR valve and not a vacuum controlled EGR valve. In addition, the valve usually has a built-in feedback system that tells the PCM (Powertrain Control Module) what position the valve is in; open, closed or somewhere in between. The PCM needs to know this in order to determine if the valve is working properly. If the PCM determines that the valve should operate, but the feedback loop indicates that the valve is not open, this code will be set. Or, if the PCM determines that the valve should be closed, but the feedback signal indicates that the valve is open, this code will be set.

Symptoms

DTC P0404 may not show any symptom other than the MIL (Indicator Lamp) or Check Engine Light. However, EGR systems are inherently problematic due to carbon build-up in the intake manifold, etc. This normal build-up can build up in the EGR valve, keeping it open when it should be closed. In this case, the engine may idle roughly or not at all. If the valve fails and does NOT open, the symptoms may be higher combustion temperatures and, as a result, higher NOx emissions. But the latter symptoms will not be visible to the driver.

Causes of the P0404 code

Typically, this code indicates either a build-up of carbon or a faulty EGR valve. However, this does not exclude the following:

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

Possible solutions

1. Command the EGR valve open with a scan tool while observing the actual EGR position (it will likely be labeled "Desired EGR" or something similar). The actual EGR position must be very close to the "desired" EGR position. If so, then the problem is most likely temporary. It could have been a stuck piece of carbon that has been shifting since then, or it could be a faulty EGR valve coil that periodically opens or closes when the valve temperature changes.
2. If the "desired" EGR position is not close to the "actual" position, disconnect the EGR sensor. Make sure the connector is supplied with a 5 volt reference. If it does not display a voltage reference, repair an open or short in the 5 V reference circuit.
3. If a 5 volt reference is available, activate the EGR with a scanner, monitor the EGR ground circuit with a DVOM (digital volt / ohmmeter). This should indicate good grounding. If not, repair the ground circuit.
4. If there is a good ground, check the control circuit. It should indicate the voltage that varies with the EGR open percentage. The more it is open, the higher the voltage should increase. If so, replace the exhaust gas recirculation valve.
5. If voltage does not increase gradually, repair an open or short in the EGR control circuit.

Associated EGR Codes: P0400, P0401, P0402, P0403, P0405, P0406, P0407, P0408, P0409

How does a mechanic diagnose a P0404 code?

• Scans codes and documents freeze frame data to confirm problem
• Clears engine codes and road tests to see if the problem returns
• Monitors the pid of the EGR sensor on the scanner to see if the sensor indicates the valve is stuck open or not moving smoothly.
• Removes the EGR sensor and manually operates the sensor to isolate a valve or sensor malfunction.
• Removes and inspects the EGR valve to make sure it has not coked, causing incorrect sensor readings.

Common Mistakes When Diagnosing Code P0404

• Do not manually use the EGR position sensor to isolate valve or sensor failure before replacing components.
• Failure to check the wiring harness and connection to the EGR position sensor before replacing the EGR position sensor or EGR valve.

How serious is the P0404 code?

• The EGR system that runs this code, the ECM can disable the EGR system and make it inoperable.
• A lit Check Engine light causes the vehicle to fail an emissions test.
• EGR position is critical for the ECM to properly control the opening and closing of the EGR valve.

What repairs can fix code P0404?

• Replacing the EGR valve if it is partially stuck open due to soot in the pin area and cannot be cleaned.
• Replacing the EGR position sensor if found to be unable to give correct input to the ECM when moved by hand
• Repair shorted or open wiring to the EGR position sensor or connector.

Additional comments to consider regarding code P0404

Code P0404 is triggered when the EGR position is not as expected by the ECM and the most common cause is a partial stuck open EGR valve due to carbon deposits on the valve pin.

How to Fix P0404 Engine Code in 3 Minutes [2 DIY Methods / Only $4.37]

Need more help with your p0404 code?

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