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EGR Trouble Code 0401

EGR valve

This is one of the most common codes thrown on cars made in the 1990s and early 2000s. The code is the exhaust gas recirculation flow warning and is commonly fixed by thoroughly cleaning the EGR valve and its exhaust feed and/or by replacing the sensor/modulator on the valve. Usually the first is tried and then the latter is done when that failed to resolve the problem. But this isn't always a fix.

As displayed in our forums recently by user Dominique and her conversation with Big Block 409 about her 1998 Tacoma, this common fix doesn't always fix the problem.

This means that, most of the time, the problem is a vacuum leak rather than an EGR valve problem and it just happens to be shown to the computer as a symptom related to the EGR. Secondary, exhaust leaks could also be an issue, as BB points out.

So let's go through the process that should have happened here instead.

  1. First, the cleaning of the EGR valve and its feed pipe from the exhaust.
  2. When that didn't work, a vacuum test should have been done.
  3. Then replacement of the EGR valve.

There are other potential problems here as well, of course. Exhaust back pressure for one. Most of the time, though, going through our three-step process will clear any P0401 issues.