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  1. #1

    Question Code P0446 Confusion

    '99 Sierra 1500, 4.3l. Problems began this time last year. Several codes came up, including p0446 and a couple of others (misfire & vacuum leak stuff). At that time, replaced plugs, wires, distributor cap & rotor, vapor canister, vc purge solenoid valve (per TSB), gas cap, & intake manifold gaskets. All codes cleared, except for p0446. Scanner indicated 2 codes, p0446 & p0446 pending. Was planning to get another emissions waiver for this year (as we're at a loss as to what to do next), so went to the inspection station & got the truck failed a couple of days ago. Then yesterday, the MIL went out. Was ready to rush back to station to get emissions passed, but decided to scan first. Scanner now gives p0446, but the p0446 pending is gone. Also, MIL is lit (stays on, not like the brief flash of all dash indicator lights) with key in on position, but goes off when the truck is cranked. Previous freeze frame data indicated p0420, & now that pending DTC is gone, freeze frame data indicated p0171 Very confused. Any ideas on where to go from here?

  2. #2
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    I moved your thread here as your issue could apply to more that just your model truck. In widening your audience, you should start getting responses/opinions.

    Welcome to the Club and good luck!


    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

    SUSPENSION: Rancho 4" Suspension Lift; Rancho RS9000XL Shocks; Rancho Skid Plates; Rancho MyRide Wireless Shock Controller;
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    ACCESSORIES: Westin Brush/Grill Gaurd; Westin Nerf Bars; Truxedo Tonneau; 20% Tint; Tow Mirrors w/Heat & Signals

  3. #3

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    Here's a long thread on the topic:
    http://www.gmtruckclub.com/forum/sho...nt-circuit-low

    Use of the search tool on this site may reveal others that are useful, too, and that may be your best bet as it's a springtime holiday weekend in the U.S. and site traffic tends to be lower on busy holiday weekends like this one.

  4. #4

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    SurrealOne, thank you for the advice. Researched on the forums and internet prior to posting.

  5. #5
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    your problem can be a tough one to fix. some it is just a bad fuel cap. a simple fix. with what you replaced [threw parts at it , no leak testing] this can occur.

    What is occurring most likely is the fuel tank/vapor lines have a leak. the fuel filler can / is a possible item. happened to me at the metal fill neck where the neck had welded metal bracket for mounting. used metal mender.

    If the tank/vapor lines etc has no leaks , then the fuel tank/pressure sender [wires/connector] may be defective. this does occur in the older vehicles.

    The vapor lines being metal and in some areas hard to see need be tested for leaks.

    disconnect both ends plug the line ends and add some air pressure like 3 -5 psi. see if it holds pressure.

  6. #6

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    Last year we had some more specific codes & took care of them. Thanks for the ideas. Will let you know results when we get to it. : )

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