I’ve been working here with a guy to sort out the causes behind the Christmas tree instrument cluster in his ’01 DII. We did the Option B bypass so the Three Amigos are gone, and he replaced the O2 sensors which addressed the engine management codes.

The only thing left to address is an EVAP code -- P0445 – Purge valve short circuit to ground.

Is the recommended remedy to replace the purge valve, or do we need to start testing circuits?

Redrover has never (not yet?) thrown any EVAP codes, so I’m new to this part of the DII canon. Thanks.

 

Maybe test power lead to ground at the connector. Should be open circuit. The ground lead should also be open circuit, if that is the ECU control wire (need to check diagram). Simple and quick ohmmeter checks right at the canister to rule out a wiring problem.

 

Obligatory mention to make sure the battery is fully juiced before going down the path of more complicated fixes. Too often that solves a lot of strange one off gremlins.

 

Thanks JohnZo. I'm self-taught with the multimeter but it took me a little while to unpack your suggestions.

I can test for 12V power at the connector with the ignition switch in Position II. I get that. What I didn't follow at first is how to check the ground lead.

As I have learned about a lot of systems in the DII (and likely other vehicles), power is supplied constantly to many components and the component operates when the ECM or BCU opens a path to earth (ground). That's the case for the door locks, for example, and according to the RAVE Workshop Manual that's how the purge valve is controlled too.

Since the RAVE description for P0445 is "Purge valve short to ground" I expect that's where the problem is. I guess the way to test the ground would be to check continuity between the purge valve connector and the corresponding cavity on the connector where the wire terminates at the ECM. That would require a looong extension from under the bonnet to the ECM, but that's doable. If there is no continuity, I guess that would mean installing an overlay wire.

I've also seen instances where simply unplugging and reconnecting a connector solves a problem. I've had that happen with an SRS fault and an ABS fault.

In the meantime I thought of another, easy to execute test. I drive Redrover very little, so I may remove the purge valve from my truck and install it in my friend's truck to see what happens. Swapping the purge valve is easy and quick.

 

Your observations regarding making and breaking ground are correct. It's a lot less load on the ECU circuitry to provide ground, the path to + is where the amp draw will be and is more challenging to regulate. "Purge valve short to ground could" simply mean the internal coil has failed and it can't see an open circuit when it's not closing the relay in the ECU, it sees ground all the time even when it shouldn't. Swap for known good is the easiest and cheapest way to pursue this one.

 

First check is the ground terminal at the valve connector (red ohmeter lead, e.g. 20 k ohm scale), then battery negative (black lead). Should get no reading (i.e. infinity). Verify using other higher ohm scales. If not infinity then there is a short to ground in that wire path, which could be fixed by installing a different wire from the ECU, or tracing the existing wire to fine where the rub or melt is and re-insulating it. Hope this is clear enough.

 

Here's an update to maybe close out this thread.

In addition to the P0445 code, the truck was running rough at idle. So based on my friend's experience and intuition, he replaced the fuel pump.

And yes, not only is the rough idle now gone, the P0445 code is gone too. I'll call that a win.