P0446 Lexus

2002 Lexus Evaporative Emissions Diagnostics (Codes P0440, P0441 and P0446)

Anyone who works on an evaporative emissions code knows there are as many possible causes as there are ways to determine the failure, says Import Specialist ­Contributor Frank Scandura, who discusses the strategy he used on a 2002 Lexus SC 430 that came in with a check engine light and evap codes P0440, P0441 and P0446.

Evaporative Emissions Diagnostics: Start With The Basics

Across the country, it’s common for car lovers to meet in random groups with their rides, hang out and share their stories, ideas and dreams — it’s something I really enjoy.

If you take a quick walk around some of these classic rides, you will soon remember what it was like to be around them all the time when they were only a few years old. It’s that strong fuel smell that reminds me of a day when fuel tanks were vented to the atmosphere. (I don’t know how more cars didn’t catch fire back then.)

We don’t have that obvious smell in vehicles anymore, as they’ve had some sort of an evaporative fuel capture system for many years.

We’ve come a very long way in reducing evaporative emissions from computer monitoring, to slosh control, non-return fuel systems. And that’s a good thing. It makes sense to stop picking up that engine heat and bringing it to the fuel tank, causing fuel to expand!

Fast-forward to Today

Laws change and technology advances. Now, we can actually “monitor” the evaporative emissions system. There are pressure sensors, electric vacuum switches, and computer-controlled activation and monitoring. But, anyone who works on an Evaporative Emissions code knows that there are as many possible causes as there are ways to determine the failure. Proper equipment and testing procedures are critical to prevent comebacks and a frustrated customer.

Recently, we had a 2002 Lexus SC 430 in for a check engine light with evaporative emissions codes P0440 – “Evaporative Emission Control System Malfunction;” P0441 – “Evaporative Emission Control System Incorrect Purge Flow;” and P0446 – “Evaporative Emission Control System Vent Control Circuit Malfunction.”

This situation reminded me of when I taught engine performance at a local community college. I always told the students that I had four rules for automotive repair:

1. Check the basics

2. Check the basics

3. Check the basics

4. See rule #1

In this case, these rules proved true (and beneficial) again. The first order of business for us when we have multiple codes for the same system (or multiple codes in general) is to determine the common factors. Our research of the code numbers revealed that all of the shared vacuum hoses or a defective fuel tank cap were the most likely trouble areas. After determining this, a basic inspection was in order, as was checking all of the shared items, starting again with the basics.

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