Evap vent solenoid

[sefiroxx]

The a evap circuit is pwm control. When truck is idle, very short or zero opening. When in motion, larger pulse width. The computer monitors afm and if it doesn't see a afm change, it will throw a code. The afm change is based on the assumption that the system is closed and when evap is opened from intake to atmosphere, a leaner condition should result. If it doesn't, then code is set.

If the system is leaking (when assumed to be closed), the lean symptom would not occur when the evap is opened.

The better scan tool is needed to command the computer to introduce a pwm signal on the ground site of the circuit.

You can partially diagnose the system without a scan tool. Disconnect the hose to the canister at the valve and install an vacuum guage. Apply vacuum and see if it holds, if not, the system is leaking elsewhere.

If it holds, connect the vacuum guage to the same hose with a T and reconnect everything. Apply vacuum, if it holds, then the solenoid/valve is sealing. If not, the valve is gone.

If holding, start engine, make sure you are in open loop (engine cold), vacuum should remain. If not, then either computer is failing or ground wire is shorted out.

If vacuum loss, stop everything. Disconnect computer harness. Check for short on the ground site using a ohm meter.

[carnau]

7 minutes ago, sefiroxx said:

The a evap circuit is pwm control. When truck is idle, very short or zero opening. When in motion, larger pulse width. The computer monitors afm and if it doesn't see a afm change, it will throw a code. The afm change is based on the assumption that the system is closed and when evap is opened from intake to atmosphere, a leaner condition should result. If it doesn't, then code is set.

If the system is leaking (when assumed to be closed), the lean symptom would not occur when the evap is opened.

The better scan tool is needed to command the computer to introduce a pwm signal on the ground site of the circuit.

You can partially diagnose the system without a scan tool. Disconnect the hose to the canister at the valve and install an vacuum guage. Apply vacuum and see if it holds, if not, the system is leaking elsewhere.

If it holds, connect the vacuum guage to the same hose with a T and reconnect everything. Apply vacuum, if it holds, then the solenoid/valve is sealing. If not, the valve is gone.

If holding, start engine, make sure you are in open loop (engine cold), vacuum should remain. If not, then either computer is failing or ground wire is shorted out.

If vacuum loss, stop everything. Disconnect computer harness. Check for short on the ground site using a ohm meter.

Again, He doesn't need to be checking for a leak. This isn't a leak code. We are all basically saying the same thing. You need a scanner that you can command the vent on and off. I checked on amazon and actually called the company to see if it has the commands. It does. This is the cheapest one I could find. https://amzn.to/2N3wf3g