Michael Sprague

Try to keep this short but give you a full history (2005 Suburban)

Few months back, wifes car became very hard to full with gas. No engine light on at this time.
replaced purge valve, vent solenoid, charcoal canister, and gas cap over the course of a few days. Charcoal canister had leaked charcoal bits into my evap lines so I used some compressed air to clear the lines.

P0455 comes on (gross leak)

Took the truck into a shop today and ran smoke test. They could not find a leak.
Replaced fuel tank pressure sensor and didnt fix issue
Discovered that the vent solenoid was working intermittently. Replaced again ( I replaced before) but same issue remained.
The auto guy reported the solenoid would stay in the "venting" state and was unresponsive to the snap on tool trying to close it. He would disappear for 10 minutes or so and when he came back it would be working fine. When he tried to run the evap test, the computer would almost freeze up and the solenoid would not be able to close. He has never seen this before, wants me to take the truck to a chevy Dealer.

Any help here before I do just that?

Michael Sprague

Too add, truck now does better with filling up with gas, but still shuts off before it is full.

tech2

tank filling: the vent solenoid is normally open and only closes for evap leak testing. the entire evap vent line must be clear for refueling...the path is: from the tank...to the evap cannister...out the evap vent solenoid...out to the evap fresh air filter. the fresh air filter and hoses can fill with dirt. gm has relocated them from the filler neck to the top of the transmission bell housing to protect them from dirt.


the p0455 monitor is a test for a large leak detection and purge operation. the pcm runs the test by opening the purge solenoid, closes the vent and expects to see a drop in pressure from the fuel tank pressure sensor. If the pressure sensor does not change:
it sets a the code.
-is there a leak? the vent must stay closed during this test. I am not sure if it times out after ten minutes?
-so can the system pull vacuum thru the purge line?
-does the fuel tank pressure sensor have reference voltage, grd and signal wiring intact...unplug the sensor and it should set a sensor high code. check the reference voltage to the sensor...probably should be 4.88volts. with a fused jumper wire, jumper the reference to signal...should set a low code...this confirms the wiring is all good.

Michael Sprague

Thank you so much for your reply.

My my understanding is that during the test, the pcm was not able to close the valve therefore reporting a large leak. This was reported to me from the auto shop.
i will see if I can get more info when I get home, currently working so this is short.

Michael Sprague

code came back yesterday after being off since my last post where we took the truck into a mechanic and he replaced the fuel pressure sensor.

During the evap test, he was having issues forcing the vent valve closed. His snap on tool would freeze up trying to close it but then after ab out 10 minutes of hanging, he said it would work fine. Whenever he attempted to run the test, it would do the same thing. He tried a different snap on diagnostic computer and also replaced the vent valve with the same exact results.

He thinks its a PCM issue and wants me to take it to the Chevy dealer. Any thoughts?

Due for an inspection this month.

tech2

i would be checking voltages and grd at the vent valve and out of the pcm. if the voltages are bad out of the ecm; maybe a ecm issue. gotta check the wiring first before replacing a module.

the ecm supplies battery power at all times (at key on) to the vent valve...closing it requires the pcm to grd the circuit; so verify its doing both

your tech can't change a pcm...dealer programming required. the dealer will replace the part on request but if they don't diagnose it...and your guy is wrong...your stuck in the middle.

Michael Sprague

thanks again for your reply. i will try to figure out how to check this and then report back
i do not have access to a diagnostic machine outside of the shop I went too but can test wiring

Michael Sprague

Pulled the connector from the solenoid today and inspecting it. No loose wires or fraying that I can see in the immediate vicinity of the connector.
I checked voltage and the hot wire gives me 12 volts, the ground wire nothing. My understanding is the ground wire should also be giving me 12 volts unless the pcm is trying to close the valve. Is my thinking correct? Next step trace the ground wire as far as I can go to see if I can find an issue?

Michael Sprague

Made a mistake, with the connector plugged into the solenoid, bout wires read 12v correctly. Just dont have a way to close the vent solenoid unless i can find a cheap scanner to do the trick.

tech2

with the connector unplugged and key on...
one wire will have battery voltage
the other wire will have no voltage
this circuit should be tested with a incandescent test light...this simulates a load to ensure the circuit can handle a load. a dvom or led test light won't do that.
=unplug the connector- back probe the power wire and grd the test light, the test light should be bright
=jumper the test light in series with the circuit.....the test light should illuminate when the scan tool commands the solenoid closed.