My 2004 Pontiac Grand Prix barely moves!!!!

the "Reduced Engine Power", problem causes the PCM to disable "Service Stability Control" and "Traction Control" turning on the warning lights to come on for those systems . The reduced engine power is because of a problem with the electronic throttle control system or as GM calls it TAC system . Reduced Engine Power Mode
When the PCM detects a condition with the TAC system, the PCM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The PCM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
• Limited throttle mode--The PCM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
• Throttle default mode--The PCM will turn OFF the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The PCM will perform the following actions:
- Limit engine speed to idle by positioning the TP, or by controlling the fuel and spark if the throttle is turned OFF.
- Ignore the accelerator pedal input.
• Engine shutdown mode--The PCM will disable fuel and de-energize the throttle actuator.
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Drive by Wire training Your best bet , take it to a GM dealer

You may have to have the harness replaced. Be sure the connector innards stay dry.When they get wet the contacts will oxidize and start shorting to each other and also the oxide is an insulator causing connections to open. Good Luck, I had a water problem with a Ford Flex and even though covered under warranty since I was the second owner they would not honor it. It cost me about three grand so price things out before getting it fixed, the car may not be worth the investment.

run fault codes to determine the failing sensor.

Have the fault codes read as a reduce power message means that something is wrong either in the engine or the gear box. check oil and coolant levels and treat the message seriously as it is intending to stop costly damage

O2 sensors can cause this and often they clear up after a good run.

hey guys, im going through the exact same thing with my 2004 pontiac grand prix. and i did my research and found a recall that described these issues. I contacted pontiac about this and they advised me to take the car to get a diagnois to make sure its a problem that relates to the recall and they will reimburse me the money it costed to get the dx and pay full cost for the problem. below im going to copy and paste all of the recall info. Hope this helps for all of us

Recall ID # 51199 - SERVICE BRAKES, HYDRAULIC

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Recall Date:

JUN 23, 2004

Model Affected:

2004 Pontiac Grand Prix

Summary:

CERTAIN PASSENGER VEHICLES WERE PRODUCED WITH LOWER THAN SPECIFIED TORQUE ON BOTH FRONT BRAKE CALIPER TO STEERING KNUCKLE ATTACHMENT BOLTS. WITH IMPROPER TORQUE, THE CLAMP LOAD AT THE JOINT MAY NOT BE ADEQUATE TO PREVENT MOVEMENT BETWEEN THE CALIPER BRACKET AND KNUCKLE.

Consequences:

DEPENDING ON WHETHER ONE OR BOTH BOLTS BACKS OUT OR FRACTURES, THE RESULT CAN BE LOCKING OF THE AFFECTED WHEEL DURING BRAKING AND AN ABRUPT STEERING INPUT IN THE DIRECTION OF THE LOCKED WHEEL, REDUCED BRAKING AND NOISE FROM THE AFFECTED WHEEL, OR SEVERING OF A BRAKE HOSE, INCREASED BRAKE PEDAL TRAVEL, AND REDUCED STEERING CONTROL. REDUCED BRAKING OR STEERING CONTROL COULD CAUSE A CRASH.

Remedy:

DEALERS ARE TO TIGHTEN BOTH BOLTS TO THE SPECIFIED TORQUE. OWNER NOTIFICATION BEGAN ON JUNE 28, 2004. OWNERS SHOULD CONTACT CHEVROLET 1-800-630-2438 OR PONTIAC 1-800-620-7668.

Potential Units Affected:

47991
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Original Launch X431 Master

I think you can take a OBD2 code reader to have a check, and you will know what problem cause the lights on.
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car diagnostic tools

a bad reading from a wheel speed sensor will cause the problem you need a scan toll to see what one is bad they also had a problem with the harness connectors so using a scan tool makes it a must

I had the same problem with my car. I cleaned the throttle body and when i installed everything back, the car would throw 2 OBD codes: P0120 at start up and P0507 when it stalled at a red light. Took it to the dealership and they had to install a new throttle body because the throttle position sensor is internal. Cost = $718.00 out the door. Part is about $480 and labor is 1.8 hours at $99.00/hr (bunch of ****). There is only a 12 month/12,000 mile warranty for work from the dealer so I would recommend doing the work yourself if possible. There is only 2 bolts on top, 2 nuts on bottom, 1 electrical connection, and 1 hose clamp.

i have an ABS, Traction Control, and Variable Steering warning lights come on right after i put the car in drive and move forward.
2005 Pontiac Grand Prix