Trouble Code P0401?

Po 300 means multiple misfire any # 1 2 3 or 4 ck plugs, wires and ck compression. And po401 I guess is egr system malfunction. Replace vacum switch valve for egr wich is on the back of the engine close to power stering pump around that area. Did help?

Retrieved code P0401 insufficiant egr flow detected. Would like to know correct repair procedure.

1999 Toyota Camry 4 cyl Front Wheel Drive Automatic

code p0401 will not go away. Changed all the components of the egr system and made shure all the passages were clear. Code p0401 still comes back. What is the problem and what monitors the egr flow?

My car has had the check engine light on. Excessive exhaust smell inside car. Throws code p0401. I have changed EGR valve. The air intake hose has a pretty bad leak too. I need to replace. Could this be causing all the trouble? I am going to replace regardless, but want to know if there may be another issue I am missing. I also had replace a part next to the EGR valve that has three vacuum lines hooked up into it. It does not bolt on or anything just snaps into a bracket that holds it in place.

I keep getting this code, even though I have now replaced ALL the components in the EGR system: EGR valve, EGR modulator, EGR Vacuum Switching valve (VSV), and all 5 of the EGR vacuum hoses. I used genuine Toyota parts. All ports and pipe are clear. Both EGR gaskets were replaced. I am getting 12 volts at one of the two terminals that connects to the VSV. Don't know what else I can do. I'm having no other codes or problems with the car. Could it be the ECU is bad anyway, even though there are no other issues? P0401 code

Yes, I know all of those tests. THE PARTS ARE ALL NEW GENUINE TOYOTA PARTS. The hose from the intake to the MAP sensor is not leaking, or plugged, and the MAP sensor holds vacuum when applied. I erased the codes and went on the Toyota EGR drive cycle and followed it exactly. It always trips the pending code during the drive cycle and the it becomes a current code on the 2nd drive cycle. The 5 EGR vacuum hoses are routed correctly.

Yes, I did. All the parts are new Toyota parts anyway. Nothing is plugged up. Is there a way to check using a multimeter to see if the ECU is switching the VSV on/off? I do get 12 volts at one of the terminals on the plug that connects to the VSV. Is the other terminal supposed to get 12 volts at times to "ground side switch" it? I'm not sure how that can be tested. Is there a way to test the ECU first?

It was the ECU. I went to the junkyard and found one for $39. I installed it and the car started and drove fine. After completing the EGR drive cycle, the readiness monitor completed and there is now no more P0401 code. I didn't have any problem with security or anything else with replacing the ECU by myself. Maybe it's newer cars in which that is the case. Anyway, the problem is fixed with a replacement ECU.

My engine is throwing a P0401 Insufficient EGR Flow error code. The engine was running smoothly, but with the error code I would not pass California smog inspection. The engine was running very smoothly so it was obviously not a major issue with how the engine was running.

After troubleshooting the EGR Valve, vacuum switching valve, and vacuum modulator, I found that the vacuum modulator was defective.

I replaced the vacuum modulator and drove two hundred miles of mostly city driving to reset the computer. Even though the engine was running pretty smoothly previously, I noticed that the engine was running even smoother after replacing the vacuum modulator.

When I brought it back to the smog test center, it immediately threw the P0401 error code again. The technician suggested cleaning the EGR down tube and driving another two hundred miles mostly city miles to let the computers reset.

What do you suggest I test next?

Also, I have noticed some mechanics refer to a bottom mounted vacuum switching valve but mine appears to be top mounted. Are there two vacuum switching valves on this vehicle, or are some top mounted while other Camry's have them on the bottom?

It has been many years since I have done my own auto repair. Back in the 1980's and early 1990's, I enjoyed do my own work on mostly 1960's to mid 1970's cars. This is my first time working on a car with (relatively) modern emissions controls. I have an engineering BS and MS and working knowledge of automotive systems, and consider myself a mid-level home mechanic.

Thank you!

I noticed that the two vacuum hoses connecting the throttle body and the vacuum modulator are showing aging signs (surface cracks) but appear to hold vacuum. They seem to be easy parts to replace to rule out vacuum leaks there. Do you concur? If I were to replace them, do I need to use genuine Toyota parts, or can I use equivalent lengths of generic tubing from my local parts store?

Thank you HMAC300. Do I need to remove the EGR Valve from the intake manifold to clean the EGR tube, or can the EGR tube be removed/cleaned with the valve in place?

My previous tests applying vacuum to the EGR valve caused the engine to stumble and/or stall. I think the EGR valve is working okay. I will take a closer look when I have removed it. The nuts to the intake manifold studs came off easily. I am currently soaking the bolts that hold it to the bottom tube in penetrating oil as they are quite frozen.

I have changed the two Vacuum Modulator to Throttle Body tubes.