99 Deville Error Codes P0300 & P0405.

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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 99 Deville Error Codes P0300 & P0405. in Past Cadillac Vehicle Discussion; I have a 99 Cadillac Deville with trouble codes P0300: CADILLAC Cylinder Misfire Detected Random Cylinders & P0405: Exhaust Gas ...
  1. #1
    Jooseman is offline Cadillac Owners Member
    Automobile(s): 99 Cadillac Deville
    Join Date
    Dec 2012

    99 Deville Error Codes P0300 & P0405.

    I have a 99 Cadillac Deville with trouble codes P0300: CADILLAC Cylinder Misfire Detected Random Cylinders & P0405: Exhaust Gas Recirculation (EGR) A Circuit Low. The car is not idling properly, surging, and hesitating. The car will not accelerate past 35 mph, even when I push the gas pedal to the floor. I've changed the spark plugs, spark plug wires, and ignition coils. Now I can't get access to the EGR valve. There is a metal clamp attached to some fuel lines blocking my access to a bolt. Do I need to take the whole throttle body off to access this screw? I wanted to take the EGR valve off and try cleaning it. Has anyone had these codes before simultaneously? Was it the EGR valve? Help anyone!!

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  3. #2
    Ranger's Avatar
    Ranger is online now Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
    Join Date
    Jun 2004
    Woodstock Ill.

    Re: 99 Deville Error Codes P0300 & P0405.

    You need to depressurize and remove the fuel rail. Based on that DTC I'd guess that your EGR valve DOES need a cleaning. Might also check your fuel pressure and check for a clogged CAT, either of which could explain not being able to accelerate past 35 with your foot to the floor.

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