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Pontiac Grand Prix DTC P1811

Q. Hi: We have a 1999 Pontiac Grand Prix GT. It is a 3.8 liter engine, automatic transmission. with 83,000 miles on it. It has a shifting problem in that it seems to shift from first to second okay, but then immediately goes into another higher gear either third or lockup, not sure. At times when cold after running three or four minutes maybe, it can die and seems to come to an abrupt halt like the brakes are on, but are not.

Pontiac Grand Prix DTC P1811

It seems to start okay again but is a bad deal in the middle of an intersection. It threw out a code P1811 and replaced the "Throttle Position Sensor". That did not fix the problem. I have heard this particular model has an internal transmission problem. Do you have any information on this?


A. I've seen a few bulletins on new design pressure control solenoids for this transmission. Sounds like yours may be a candidate! Do you have an extended warranty?

Section: 07 - Transmission/Transaxle
Bulletin No.: 0O-07-30-002B
Date: July, 2002

Slips, Harsh Upshift or Garage Shifts, Launch Shudders, Flares, Erratic Shifts and Intermittent Concerns, DTC P1811 or P0748 Set (Replace Pressure Control Solenoid Valve Assembly)

1997-1999 Buick Riviera
1997-2002 Buick Park Avenue
1998-2002 Buick LeSabre
1999-2002 Buick Regal
2000-2002 Buick Century
2002 Buick Rendezvous
1997-2001 Chevrolet Lumina
1997-2002 Chevrolet Monte Carlo
1999-2002 Chevrolet Venture
2000-2002 Chevrolet Impala
1997-1999 Oldsmobile Eighty Eight
1997-2002 Oldsmobile Silhouette
1998-2002 Oldsmobile Intrigue
2001-2002 Oldsmobile Aurora (3.5L)
1997-2002 Pontiac Bonneville, Grand Prix
1999-2002 Pontiac Transport/Montana
2001-2002 Pontiac Aztek
with Hydra-Matic 4T65-E (RPOs MN3, MN7, M15, M76)

Some owners of the above vehicles with a HydraMatic 4T65-E transaxle may comment on harsh upshifts or harsh garage shifts, soft shifts, shudders on hard acceleration, or shifts erratic. These conditions may appear intermittently or set a DTC P1811 or P0748. During diagnosis, a low or high line pressure (actual versus desired) may be observed.

The above condition may be due to any one of the following which may affect line pressure output:

  • Sediment inside the pressure control (PC) solenoid valve, causing the PC solenoid valve to mechanically bind.
  • Sediment in the valve body, causing the torque signal regulator valve to stick.
  • Incorrect transaxle oil level.

Additional Information provided courtesy of AllDATA

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