What is p0401 in Toyota Camry 2001?

Answer 1

It means that you have insufficient flow in your exhaust gas recirculation (EGR) system.

3 key components, EGR valve, vacuum modulator, and vacuum valve (VSV). Can be any of these. To diagnose start with following. I just fixed my 2000 Camry LE 4 cyliner ( p401 code ) per below. Get the emissions diagram on line or from a Hayness manual if you don't know where these components are.

1. Reset the trouble light by removing the EFI fuse for a few minutes. Its located in the major fuse box next to the battery - black squarish fuse. Make sure you really have a problem and not a fluke. My light came on again after 3 start/stop cycles.

2. Assuming the trouble light returns, start with cleaning the vacuum modulator valve filter. The plastic cover snaps off. Clean the small round filter with compressed air or if you don't have that I used a can of computer keyboard cleaner. Check the modulator valve with engine on and at 2500 rpm to make sure flow is open and closed. If modulator doesn't work right, replace it (about $50 at Toyota).

3. Check and blow through all vaccum lines to make sure there are no obstructions.

4. Reset the trouble light again and hope problem is resolved. This was all I did to fix my Camry. If light still on -

5. VSV is next most likely culprit. From reading other posts this is common problem on Camrys and challenging to replace (Google procedure) as tight location. Before replacing either the VSV or the actual EGR valve follow the procedure for testing the EGR (need vacuum gauge to make sure EGR is functioning.

6. Assuming EGR is functioning, its probably time to attack/test and or replace the VSV.

good luck