Pontiac Grand Prix P0420 Catalyst And P1811 Transmission Codes

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.

pontiac grand prix

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.

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.

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