Need tip for CEL on 2005 2500 Suburban

[Davis]

I took my 2005 2500 Suburban by a local parts store today to see what code was stored and they said it is a P0496- Evap Flow during a non-purge condition. The CEL came on yesterday. It has the 6.0 engine. Do any of you have some advice on what could be wrong ? Thanks Davis

[ROBERT CROSS]

Purge or vent valve leak, system might need a "smoke" test to know for sure. Stop at a GM Store & ask, they should be able to help.

I would do it myself for you but I've recently been "Bushed" from my retirement job at the Chevy Store.

[SteveH]

I have a friend that got a code simular to that on a Chevy Trailblazer, and the problem was a bad gas cap.

[ROBERT CROSS]

Originally Posted by SteveH

I have a friend that got a code simular to that on a Chevy Trailblazer, and the problem was a bad gas cap.

Yep that'll do it, most locking caps are a no..no.

[Airslide]

That little smoke tester has saved my technicians so many hours its unbelieveable. You will find small leaks everywhere and one major one causing the CEL light to come on. Most of those systems monitor leak detection down to 1mm leakage. Now introduce a fuel cap thats not threaded on correctly or defective and you just introduced a 2inch leak (size of the fuel neck opening)

Some shops have made the investment (around 700 dollars) and most dealerships have it as a required tool. Could also be one of the valves not closing properly to run the test. They should be able to figure it out easily.

Good luck

Vin

[Davis]

Thanks for the replies. The gas cap is the factory one and I have loosened and retightened to make sure it was not at fault unless it has failed in some way.Do the gas caps go bad ?

[Guido]

Originally Posted by Davis

Thanks for the replies. The gas cap is the factory one and I have loosened and retightened to make sure it was not at fault unless it has failed in some way.Do the gas caps go bad ?

Yes. You can also have a vacuum hose cracked, either near the valve or on or near the tank. Most lines in between are steel or hard plastic, and seldom go bad unless damaged by a rock or accident.

[Davis]

I used a scan tool to check the codes myself and it still has the P0496 code in it. The gas cap checks out good. I did see one thing in the data list which was EVAP purge solenoid com 0% and this was at idle and did not change even while revving the engine. I checked this on my wifes suburban with the 5.3 eng and hers did have a reading of 18% while idling and would fluctuate. I am not fluent with the technology of these newer subs so if anyone thinks that this could be the culprit for the P0496 code then I will change the purge valve solenoid. All hoses looked good. Thanks Davis

[Guido]

I did a little research on that code, and it seems to be for either manifold vacuum in the system when it shouldn't be, or loss of vacuum with the truck turned off. Check for a bad or sticking purge valve.
If the Evap purge valve does not seal properly, fuel vapors could enter the engine at an undesired timing causing drivability concerns. The control module tests for this by commanding the EVAP purge valve OFF closed and vent valve ON closed, sealing the system, and monitoring the FTP for an increase in vacuum. If the control module detects that Evap system vacuum increases above a calibrated value, DTC P0496 will be set.

[Davis]

Thanks Guido,
I will check with the local dealer tomorrow and see if they have a purge valve in stock .

[ROBERT CROSS]

[quote=ROBERT CROSS;656960] Purge or vent valve leak, system might need a "smoke" test to know for sure..[/quote

I thought so....

[Davis]

Hi, I replaced the purge valve last Thursday and so far no CEL or any other problems. Thanks for the help everyone.

[Airslide]

It may take several drive cycles for the check engine lite to reappear if the control unit detects a fault. Keep an eye on it. Lots of in town driving with a few freeway trips should get it to post again if its going to be stubborn. Sounds like you got it though.

Vinnie

[ROBERT CROSS]

That goes for the monitors also, it may take several drive cycles to clear them, they can be checked with the TechII. If the light stays off for 100mi you should be good to go.