Code P0400; EGR System

ANSWER : Hi there. The Exhaust Gas Recirculation (EGR) valve may be not designed for the emissions requirements for U.S. standards. If the EGR is pulling from cylinder number 4 and after replacing the EGR and the computer detects a misfire, then the EGR is malfunctioning and not responding. When you close off the tube to the EGR and the EGR light comes on and the misfire light goes out, then the EGR is not responding to your emissions system. I recommend replacing the EGR with the OEM specified part for the engine and all of the issues should go away. If you need further assistance with your misfire and EGR, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : Hi there. The Exhaust Gas Recirculation (EGR) valve may be the wrong one or the cheap design could be not designed for the emissions requirements for U.S. standards. If the EGR is pulling from cylinder number 4 and after replacing the EGR and the computer detects a misfire, then the EGR is wide open and not responsive. It is clearly the EGR as when you close off the tube that the EGR light comes on and the misfire light goes out. I recommend replacing the EGR with the OEM specified part for the engine and all of the issues should go away. If you need further assistance with your EGR and misfire, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : If your test results for KD5 and KD7 are accurate, there is a short between the PCM and EGR stepper motor. Your readings indicate both a short to ground and power, so my guess is that the four wires inside the harness are shorting against each other as well as to chassis ground somewhere. You’ll need to trace and visually inspect the wiring harness to determine exactly where the problem is. These test results seem odd, so it might be best to have your check engine light problem diagnosed by a professional, such as one from YourMechanic.

ANSWER : If you checked the EGR valve and cleaned it, the first thing to do is to start and idle the engine and use a vacuum pump or source to pull open the EGR valve to see if it makes the engine run rough.

It should cause the engine to run rough if the passages are clear. In the EGR tube there is a temperature sensor that can be removed and cleaned of carbon. If it has carbon build up, it can cause inaccurate EGR readings and code P0400. Run engine warm and at around 2000 RPM’s and see if EGR is being opened by the EGRC or there is vacuum on the hose to the EGR valve. Check the purge valve to see if it’s leaking vapor all of the time.

ANSWER : The code P0405 and a rough idle is most likely due to carbon getting into the EGR pintle. This will hold the EGR open. When you are getting the rough idle you should shut off engine and remove EGR valve. Check to see if carbon is holding the pintle open. If it is then you will have to remove the carbon from the pintle. Then try and clean out the EGR passages by scrapping them using a round wire brush. Afterwards, start the engine for a few seconds with valve removed to blow out loose carbon. You should then spray a small amount of carbon cleaner into the passages to dissolve the carbon. Lastly, reinstall the EGR and reset the light and codes.

If you’d like assistance with this, consider YourMechanic, as a certified professional can come to the vehicles locations to perform these checks and properly diagnose your Check Engine Light.

ANSWER : Code P0400 does not necessarily mean that there is something wrong with the EGR valve itself. The only way to condemn the EGR valve is to directly test it. In particular Code P0400 includes a circumstance where the EGR passages are simply blocked with carbon and thus little or no exhaust gases can flow into the intake manifold. Code P0400 also includes the possibility that the EGR valve is not opening due to no vacuum opening the valve from the EGR control solenoid. If the valve is electronically controlled, there could be a fault in the circuit. If your vehicle is equipped with an EGR temperature sensor, if the sensor is plugged with carbon, it can’t register a temperature change when the EGR valve is opened, signifying flow. The point is Code P0400 can never be interpreted as the EGR valve has failed. The only way to determine if an EGR valve has failed is to directly test the valve. To resolve this, that is perform a complete system diagnostic and find the root cause for the code having set, the recommended service is an EGR system diagnostic. If you request that service, the responding certified mechanic will get this fully resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

ANSWER : Hi there. Look to see where the EGR (Exhaust Gas Recirculation) is plumed into the engine. If the EGR is plumed into the cylinder number 3 and the EGR has a leak, then the cylinder number 3 will be weak and cause a misfire. If the EGR is plumed into the exhaust pipe, then the spark plug on the cylinder number 3 could have failed as the engine changed in temperature when replacing the EGR transducer. If you need further assistance with your engine misfire, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : Hi there, the short answer to your question is no . A PCM with a P0601 (which is a memory module error in the PCM) cannot reliably retrieve codes for the codes you list (P0118 – coolant temp sensor, P0123 – throttle position sensor, P0193 – fuel rail pressure sensor.

Most likely, the P0601 prevents the PCM from getting any codes from the engine sensors. The memory module error may cause in data corruption for collected sensor values, lose of data over multiple sampling periods, or failure of the data collection to work at all. Replacing the PCM was a necessary expense.

If you need assistance with the "new" codes, I would recommend having a Check Engine Light inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose the new error codes and get an accurate assessment of the repairs needed.