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PO449 code

Indy

By Indy
in Ask A GM Technician

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Indy Enthusiast

Indy

Posted
Posted

I have had a code PO449 for a long time now. I replaced both the front and rear vent valves and solenoids (the one on the engine and the one on top of the gas tank). I also replaced the gas cap. The check engine light still comes on every second cycle after resetting it. I don't want to spend a fortune at the dealer but the light is bugging me. Once the light is on for this minor problem, I have no way of knowing if another problem is present until I read the code.

I have a '99 GMC Sierra 5.3 auto 4x4.

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

The one on the tank is the one that's involved in that DTC. The one on the engine is the purge solenoid and not involved. The gas cap or a leak somewhere has nothing to do with this DTC. It's purely a control issue.

 

P0449 says that the PCM is not seeing the voltage potential it wants to see when the vent valve is off or commanded on. Could be the solenoid, which you've replaced and eliminated I'd say, so that leaves wiring or the PCM itself. PCM would be my very last choice, but it remains a possibility.

 

Do you have power at the pink wire of the vent solenoid connector when the key is on? If so, that leaves the control circuit as the suspect. You may have an open somewhere in that wire from the solenoid to the PCM. Or it could be right at one of the terminals in the connector at the vent valve or at the PCM. There's also an inline connector that's under the UBEC (underhood fuse box).

Indy Enthusiast

Indy

Posted
  • Author
Posted

I tested the only pink wire I could find leading to the back of the truck and got 9V. I can't get to the vent solenoid without major labor. I removed the fuse box cover and found 2 connectors that seem to lead to the back of the truck. Is that them or do I have to remove the fuse block itself to get underneath?

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

I've never had to look for the connector under the UBEC, so I couldn't say exactly where it's located.

 

9 volts is low. Most pink wires are ignition power and should be very near to whatever battery voltage is.

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