P0401 and p0402

Maintenance/Repairs
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1

i have a 98 toyota camry that i cant get these two codes to go away any help

2

Have you tried cleaning the EGR valve?

Tester

1 Like
3

yes and than replaced it

4

p0401 (for the 4 banger engine) is saying the computer is commanding the EGR valve on, but when it measures the intake manifold vacuum, the vacuum reading there isn’t consistent with the EGR being on. When the EGR turns on, that’s sort of like a vacuum leak, so the intake manifold vacuum should diminish a little. On your engine the vacuum reading isn’t going down sufficiently to please the computer for some reason.

My Corolla’s EGR configuation is pretty much identical to the 4-banger version fro the 98 Camry

The computer’s control of the EGR is via an electric-selenoid operated vacuum switching valve (VSM). When the VSM is commanded on, the amount of EGR to actually apply is determined by another gadget, the EGR modulator. The EGR modulator has vacuum hose inputs from the throttle body, and a vacuum hose output to the EGR valve. So the problem pretty much has to be one of these

  • VSM faulty
  • EGR Modulator faulty
  • Computer faulty
  • Wires from computer to VSM faulty
  • EGR valve faulty
  • Problem w/ vacuum hoses between throttle body and modulator and EGR
  • Device that measures manifold vacuum is fault (MAP)
  • Throttle body problem
  • Manifold vacuum is incorrect, but this would usually create other very noticeable problems

One other idea, if this is a Calif car (like mine), it probably has a special Calif EGR. The Calif EGR contains a thermistor to measure the EGR’s temperature. This measurement is also used by the computer to verify the EGR recirculation is correct. So if a Calif car, that part has to be working too.

Where I’d start w/that problem is connect a hand-held vacuum pump to the EGR vacuum input, warm the engine to normal operating temperature, and see if applying vacuum to the valve turns it on and stalls the engine or not. If the EGR valve is working I’d guess the problem is the VSM, its electrical connections, or the vacuum hoses. It’s very easy to get those vacuum hoses connected to the wrong place. Ask me how I know … lol …