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2004 Reduced power and won't drive

01-27-2008, 10:34 AM
2004 Pontiac Grand Prix, not supercharged, 61,000 miles. Reduced engine power message and service traction control message. Will start put nothing happens when pushing the gas pedal, pulled codes p0120 and p1516. I saw another thread about changing the throttle body but hoping maybe there is another cause. Any help would be appreciated.

01-27-2008, 11:28 AM
p1516?? I couldn't find any info on that DTC. Maybe the following will help for P0120.

Document ID# 1214909
2004 Pontiac Grand Prix
DTC P0120
Circuit Description

The throttle body assembly contains the following components:

* The throttle blade
* The throttle actuator motor
* The throttle position (TP) sensor 1 and 2
* The throttle actuator control (TAC) module

The TAC system monitors the throttle position with 2 sensors. If the powertrain control module (PCM) receives a message from the TAC module that indicates TP sensor 1 voltage is outside a predetermined range, DTC P0120 will set.
Conditions for Running the DTC

* DTCs P0606, P1518, P2108 are not set.
* The ignition switch is in the crank or the run position.
* The ignition voltage is more than 5.23 volts.
* The communications between the TAC module and the PCM must be valid.

Conditions for Setting the DTC

The TP sensor 1 voltage is less than 0.376 volts or more than 4.506 volts.


The PCM learns a minimum throttle position of more than 0.714 volts.


The TP sensor reference voltage is less than 4.54 volts or more than 5.21 volts.
Action Taken When the DTC Sets

* The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
* The control module commands the TAC system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.






Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views


Did you perform the Diagnostic System Check-Engine Controls?


Go to Step 2

Go to Diagnostic System Check - Engine Controls


1. Turn ON the ignition, with your foot OFF the accelerator pedal and the engine OFF.
2. Observe the TP sensor voltage parameter with a scan tool.

Does the scan tool indicate voltage within the specified range?

0.38-0.71 V

Go to Step 3

Go to Step 5


Fully depress the accelerator pedal.

Does the scan tool indicate the voltage is within the specified values?

0.71-4.51 V

Go to Step 4

Go to Step 5


1. Observe the DTC Info with the scan tool.
2. Depress the accelerator pedal to wide open throttle (WOT), then return the pedal to closed throttle.

Did this DTC fail this ignition?


Go to Step 5

Go to Intermittent Conditions


Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?


Go to Step 6



1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?


Go to Step 2

Go to Step 7



Be aware that repairing one individual condition may correct more than one DTC.

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?


Go to Diagnostic Trouble Code (DTC) List

System OK
Document ID# 1214909
2004 Pontiac Grand Prix

01-27-2008, 01:16 PM
Thanks for the quick reply Headnsouth. That looked like a lot of work so I took off the throttle body, cleaned it up good and put it back on. Cleared the codes and now everything is good, don't know if maybe the connector had worked itself loose or something.

01-27-2008, 01:37 PM
Kewl! Glad that fixed it. :)

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