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Hi,
I have a 1997 Neon and have a check engine light with the extracted code being 31 (a fault in the evap purge solenoid circuit). I pulled out the solenoid and checked it with a 12v source and it is fine. When 12v is applied it clicks and I can blow through it, when I remove the 12v I cannot blow through it. I checked the resistance and it is approx. 30 Ohm.

After reinstalling the solenoid:
When I turn the key to the start position (or turn engine on) I read 12v (or higher) on the wires going into the solenoid when disconnected from the solenoid. However, the moment I connect it to the solenoid, the voltage drops to zero right away (no clicking or anything). It is as if the PCM is supplying voltage, but is unable to supply the current needed to activate the solenoid. Is something wrong with the PCM / is there anything I can do to fix it ?

Also, with the engine running I checked the hoses going into the solenoid and one is definitely pulling a vaccuum, so I think that is fine. Also, on the wires going into the solenoid, one wire is definitely to chasis ground and the other is not (as I would expect). I also looked for an worn away / shorted wires, but could not find any.

Any ideas,
Mike
 

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Welcome to Allpar. It does sound like a poor connection or high resistance is causing the 12 volts to drop when a load is placed on it or that the purge solenoid return wire is grounded all the time.
The 12 volts into the purge solenoid is supplied on the Gn/Wt wire from fuse #10 (15A) in the underhood fuse/relay box (PDC). This circuit also supplies the t/converter lock-up clutch solenoid, LDP (leak detection pump), EGR transducer solenoid and fused ign into the PCM. If these other components are receiving good power, then there may be a high resistance in splice S109 or more likely a grounded return wire from the solenoid back to the PCM.
The PCM turns the purge solenoid on and off (a duty cycle)through the ground-side of the solenoid, a Pk/Bk wire. This wire should not read chassis ground, I believe that you have a pinched or rubbed-through wire if this is the case.
The hoses sound OK, one side is manifold vacuum switched by the solenoid and the other comes from the charcoal canister.
 

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You have a wiring short somewhere. Pulling the voltage down to ground indicates a short circuit. Since the solenoid itself tests OK, it must be the wiring harness.
 
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