How to Test and Repair your EVAP Valve

Ready to test and repair your EVAP Valve?

The purge valve is a common failure item on the Volvo 850/x70 series. This is a great how-to with easy-to-follow pictures for a fix to avoid buying a new valve.

I have adapted this from my original tutorial for the BMW M30 engines. They both use Bosch systems and the valve is identical. What happens is that at startup the valve stays open to draw fumes caught in the charcoal canister. The fumes are there because they evaporate from the fuel tank. This is why your gas cap is usually checked at emissions inspections and why the manual says you may have a temporary check engine light when you fill up with the car on. The only place evaporating gas can go is the charcoal canister which is then pulled into the intake at startup.

This is pretty much always the P0455 code.

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I have adapted this from my original howto for the BMW M30 engines. They both use Bosch systems and the valve is identical. What happens is that at startup the valve stays open to draw fumes caught in the charcoal canister. The fumes are there because they evaporate from the fuel tank. This is why your gas cap is usually checked at emissions inspections and why the manual says you may have a temporary check engine light when you fill up with the car on. The only place evaporating gas can go is the charcoal canister which is then pulled into the intake at startup.

This is pretty much always the P0455 code.
http://www.obd-codes.com/p0455

how to test it according to the official service manual

Get a 12v source with some alligator clips – I used a power supply for an external hard drive. It was 3 amps but you should be able to use 1 amp.

Get a vacuum source – preferably with a gauge on it. Attach it to the larger port on the valve.

Energize the valve with your 12v source, then pump the vacuum up. It should hold at least 50 milibar for 20 seconds. It probably won’t. You don’t need a vacuum gauge, just get a rubber squeeze bulb, squeeze it, and it ought to stay deflated. If it doesn’t, you should fix or replace it.

You can also test the harness to make sure it isn’t an electrical problem. The two pins ought to have 12 volts always when the car is running.

What you need:

• Tube of RTV. I used sensor safe Ultra Black but you can probably use anything, that’s what I had on hand.
• Thin blade flat head jeweler’s screwdriver.
• Some Q-tips.

Procedure

1. Open it up. This is a pain but if you take your time you should be fine. Get a jeweler’s screwdriver and stick it between the seam of the valve. You will be breaking the glue seal so you need to use some force but don’t get sloppy – just take your time and pry all around gradually.

2. You will have two halves – one side has a little plastic thing that holds a spring against a rubber stopper. Not sure what this is supposed to do – maybe prevents backflow.

The other side has the business end. This is the electromagnet that causes the valve to close. The coil energizes and pulls the flap in the middle closed.

3. Pry it out gently. You will see there is an o-ring which is probably petrified. I suppose if you wanted to, you could find an o-ring that fits and use it instead of the RTV fix. I had RTV on hand an no o-ring so I went that route. You will still need to seal it back together with RTV but you don’t have to glop it in to seal the bottom.

The slots are for using a screwdriver to adjust the gap for the flap (on the metal spring on the other side, don’t mess with it).

4. Get your RTV and Q-tips. Put a reasonable amount of RTV in the housing for the electromagnet. Don’t forget to put some in down the inside of the hose barb but not too much that it might seal it shut.

I had tried to reassemble without the O-ring but it wasn’t keeping a seal because there was too much empty space.

5. Stick the electromagnet back in, you will see there is a cutout for the connector, it is in the bottom right on the picture above.

6. You can test now by applying a vacuum and 12v. It should hold vacuum.

. Reassemble the two halves, make sure the little rubber plunger thing works – just stick the jeweler’s screwdriver in and you should feel it move.

7. Slather on some RTV around the seam and let it sit overnight.

8. You’re DONE!!!

Read the rest of this fine tutorial w/ photos: How to test and repair your EVAP valve

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Last Updated on March 16, 2022