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.
Answer:
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.

The
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.
Pontiac grand Prix P0420 Catalyst Code
P1811 Transmission Codes

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