Code P0496 - what to do?

[hesster]

I have posted numerous times on a issue of a No start or Start and die on my 2010 Whipple Blown SS. Never had any codes UNTIL NOW. So I was chasing my tail looking for root cause, and have had a few different Tuners try to address it. So this may be a long post, but looking for input from my fellow members.

When leaving the local Cruise night last Monday the car did not start until the 4th attempt, and only started after mashing the Throttle a few times. Got home and hooked up the HP Tuner and there it was - finally- a clue as to what the issue may be.

P0469 which is Purge Solenoid Valve Leak
"If the evaporative emission (EVAP) purge solenoid valve does not seal properly fuel vapors could enter the engine at an undesired time. If the control module detects that the EVAP system vacuum increases above a calibrated value, DTC P0496 will set."

Yep - that seems to possibly be a reason for the hard starts, as maybe the Purge Solenoid is stuck open or PCM is keeping that open, puking Fuel Vapors into the Blower, and that makes it hard to start. AND, when I mash the Throttle, that opens the TB Blade and that "airs out" the vapors, and allows the car to start?

So why the Code now? My current Tuner said my previous Tuner(s) turned any EVAP Codes OFF, so that hid any chance of seeing this issue. His tune turned these codes BACK ON.

My options are to maybe figure out how to use the HP Tuner Scanner's "Controls and Special Functions" feature to cycle the Solenoids and observe Fuel Tank Pressure as a indicator of a fault. Don't know how to exactly do this, and don't want to damage anything.

Or just REPLACE the (2) Solenoid Valves. Maybe start with the easy one in the Engine Bay, then attempt the one at the Charcoal Cannister which is a nightmare for access. Gotta figure out correct Part numbers for these.

Whatever it takes, and any input is welcome!

[gtstorey]

I would chase the loss of ECM power as mentioned on HPT forum before I would worry about the Evap system. Verlon is one of the smartest guys on there for GM stuff.

[gtstorey]

Verlon: "Yes, it's a Powertrain Relay. Try connecting #194 bulb to the relay coil and look will the light go out when the engine stalls."

Visual inspection only goes so far. Even voltage checks can be misleading since a voltmeter doesn't load a circuit. I would probably start with the bulb attached to the switch side of the relay vs the coil side, but Verlon may have a reason for pointing to the coil. But eventually my may need to check throughout the harness to find a problem.

[gtstorey]

No clue on which relay it is without looking at the fuse box label or service manual.

Easiest way to test and connect would be a "Relay Buddy" or tester (basically a relay breakout harness) or make your own. Beyond that, you can tap into the harness, probably with some sort of piercing probe.

[gtstorey]

Back to the original purge valve question, You could probably cap and/or disconnect it to check whether it is causing the hard start.

And this could be a simple tuning issue. And have you checked fuel pressure especially when it doesn't start? Have you checked to see if it isn't firing when it won't start. Are the plugs wet when it won't start? etc...

[gtstorey]

Data log pressure isn't a replacement for a diagnostic fuel gauge.

Whether it is actually firing won't show up in a data log. Try spraying it with some flammable brake cleaner when it won't start.

New plugs and looked fine don't really answer the question "are they wet with gas" when it won't start.

BCM isn't the same as ECM.

At some point you have to try and figure out what is not there to make it not start. No Fuel, no spark, too much fuel, etc. I know this can be hard to figure out on an intermittent problem.

But 0 volts to the ecm will definitly do it.

[acutron42]

I pulled this from alldata, not sure if it will help or not. I deleted the hot links as they would make the post confusing. If you need any other info let me know.

Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0496
Evaporative Emission (EVAP) System Flow During Non-Purge

Circuit/System Description
This DTC tests for undesired intake manifold vacuum flow to the evaporative emission (EVAP) system. The engine control module (ECM) seals the EVAP system by commanding the EVAP purge solenoid valve OFF and the vent solenoid valve ON. The ECM monitors the fuel tank pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is more than a predetermined value within a predetermined time, this DTC sets.


The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP purge and vent solenoid valves.

ECM Command EVAP Purge Solenoid Valve EVAP Vent Solenoid Valve
ON Open Closed
OFF Closed Open


Conditions for Running the DTC
DTCs P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0464, P0608, P0609, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138 are not set.
The ignition voltage is between 11–32 V.
The barometric pressure (BARO) is more than 70 kPa.
The fuel level is between 10–90 %.
The engine coolant temperature (ECT) at start-up is less than 35°C (95°F).
The engine off time is 8 h or more.
The intake air temperature (IAT) is between 4–30°C (39–86°F).
DTC P0496 runs once per cold start and no more than 17 min when the above conditions are met.
Conditions for Setting the DTC
The ECM detects more than 10 in H2O vacuum for 5 s during a non-purge condition.


Circuit/System Verification
Ignition ON, engine OFF, seal the EVAP system using the Purge/Seal function with a scan tool.
Start the engine.
Observe the FTP sensor with a scan tool. The FTP sensor parameter should be less than 1.7 V after 90 s.

If the FTP sensor parameter is greater than the specified range, go to Circuit/System Testing.

Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.
Circuit/System Testing
Ignition ON, engine OFF.
Seal the EVAP system using the Purge/Seal function with a scan tool.
Start the engine.
Observe the FTP sensor with a scan tool. The FTP sensor parameter should be less than 1.7 V after 90 s.

If the FTP sensor parameter is greater than the specified range, replace the Q12 evaporative emission purge solenoid valve.

Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.