What is the meaning of codes P0401 and P0301 - 2003 Chevrolet Impala

Code P0301 indicates a misfire in cylinder 1 of your 1996 Toyota Corolla 1.6L1. The most common causes of this issue are faulty spark plugs, worn-out spark plug coil packs, or faulty ignition system 123. You mentioned that you have already replaced the spark plugs, spark plug wires, distributor cap, and rotor button. However, it is possible that the new parts you installed are faulty or not installed correctly. You may want to double-check that the spark plugs are gapped correctly and that the spark plug wires are connected to the correct spark plugs

Code P0401 indicates a problem with the exhaust gas recirculation (EGR) system . The EGR system is responsible for reducing the amount of nitrogen oxide (NOx) emissions from the engine. The most common causes of this issue are a faulty EGR valve, clogged EGR passages, or a malfunctioning EGR vacuum modulator . Since you have already replaced the PCV valve, it is possible that the new part is faulty or not installed correctly. You may want to double-check that the PCV valve is installed correctly and that the EGR valve is functioning properly. If these two code problems persist, it is best to take your car to a trustworthy repair shop to diagnose the issue as quickly and accurately as possible .

Here's a link on your P0301 code. P0301 OBD II Trouble Code Here's the link for the P0401 code. P0401 Saturn Exhaust Gas Recirculation Flow Insufficient your egr passage may be blocked.

P0401 is EGR problem
P0300 is a cylinder 3 misfire.
Replace EGR valve and do a full tune-up.

P0401 Code:
Exhaust Gas Recirculation (EGR) Flow Insufficient
https://curateview.com/p0401-code/

P0155: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
P0301: Cylinder 1 Misfire Detected
P0401: Exhaust Gas Recirculation Flow Insufficient Detected

Code P0301 ts Cylinder 1 Misfire Detected. Check the spark plug and wire on cylinder #1.

p0136 and p0141 are o2 sensors and p0401 is a egr flow and the p0171 means its running lean on low bank 1

There could be a hundred causes for a check engine light. First step is to hook up a computer scan tool and see what codes the computer has. The next step depends on the codes.

A code P0303 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

A. P0401 "Exhaust Gas Recirculation Flow Insufficient Detected" that there is not enough exhaust gas being admitted to the engine.
There are a number of things you can check, and others you need a scan tool to check.
What you can do is check for vacuum to the EGR valve. You can remove the EGR valve and see if it is stuck closed. Test it with a hand vacuum pump and see if it opens smoothly. Check the EGR valve orifice and make sure it is free and clear. Check and clean the EGR passages in the going to and from the EGR valve.
If this checks out, then the Differential Pressure Feedback EGR system will need to be scanned to check the EGR sensors and switches

A code P0301 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

P0401 Exhaust Gas Recirculation Insufficient Flow Detected

P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0305 Cylinder 5 Misfire Detected


I would check out the EGR valve. That maybe what is causing all the misfires.