2003 Pontiac Grand Prix GT 3.8L Series II 3800.GM Code P0420 (catalyst efficiency low bank 1)
P1811 (max adapt and long shift).

Oil changes every 3k, 2 transmission flushes and a transmission service, and the catalytic converter
was replaced at 105k.

I have a 2003 Pontiac Grand Prix GT with a
3.8L Series II engine. I am having 2 different issues with
this vehicle. First, the transmission has started jerking hard into gears. It seems that it only does it
once the car gets up to a normal operating temperature. I will be stopped at a stop sign or stop light
and once I start going the engine revs to about 1800 rpms and the transmission jerks into 1st and
also shifts hard into 2nd and 3rd. I have had an SES light come a few times and had a friend of
mine who owns his own mechanic shop hook his Snap On Verus (a $10,000 computer scanner) into
it and it listed the codes P0420 which I believe was the catalyst efficiency low bank 1 and P1811
which was maximum adapt and long shift. I have also wondered if the transmission is even shifting
out of 3rd and into overdrive because the RPMs are approximately 3100-3300 while driving
65-70MPH down the highway.

My wife has a 2007 Pontiac Grand Prix GT like mine only with the super charged motor and her car
runs 75MPH and the RPMs are about 2100. My mechanic said it could possibly be the PCM or
Pressure Control Solenoid, but he wasn't all that sure because he doesn't exactly specialize in
transmissions or repairs to them. Any help with this would be much appreciated. And the other issue
I am having that is getting to be a real pain is the ignition. Occasionally, when I go to shut the car off
my key does not turn back to the OFF position for me to remove it. It gets stuck in the ON position. I
have noticed that when you put the car in PARK and let off the brake, you can tap the shift lever
button on the shifter repeatedly and hear a clicking sound coming from the steering column.
Sometimes you hear it and sometimes you wont. I have determined that when you dont hear the
clicking sound by depressing the shift lever button your key will not fully rotate to the OFF position.

Use to, when I would put the car in PARK I would listen for that sound and if I heard it click, my key
would not get stuck in the ignition and when my key would get stuck,I would have to keep tapping
that button on the shifter until I heard that clicking noise coming from the column. Now, my key is
stuck in the ignition every time I shut my car off and try to pull the key out. So I have to keep a little
tool in my car to stick up in the hole on the bottom of the steering column and push up on the
plunger just so I can remove my key. Its very annoying and any help or advice you have for me
would be very much appreciated. Thank you sincerely for your time.

WOW that was a lot to go over. Well, the trans shifting and the code P1811 is usually the pressure
control solenoid.I would suggest removing the pan and look for any debre, as this would be sign
that something internally has failed and caused the P1811, and not the pressure control solenoid.

catalytic converter code may have come back because of the converter. If you installed an
non-factory part, the cheaper ones are know for not cleaning the exhaust good enough. The key
not turning or coming out is one of two common problems. Most common is that the solenoid in the
shifter is faulty. Especially if pop or coffee has ever been spilled down there. Less common is the
actual release solenoid in the column.

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Pontiac grand Prix P0420 Catalyst And P1811 Transmission Codes