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Tim's Auto Repair
Tim's Auto Repair, mechanic
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Experience:  Have owned a repair shop for 25 yrs.
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2003 chevy suburban dtc p1125

Resolved Question:

2003 chevy suburban dtc p1125
Submitted: 7 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 7 years ago.



the problem may be the throttle acuator on the throttle body...this can also cause this code to show up


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Description and Operation


Throttle Body Assembly
The throttle body for the TAC system is similar to a conventional throttle body with a couple of exceptions. One exception being the use of a motor to control the throttle position instead of a mechanical cable.

The other exception is the new design Throttle Position (TP) sensor. The TP sensor mounts on the side of the throttle body opposite the throttle actuator motor. The TP sensor is actually 2 individual TP sensors within one housing. Separate signal, low reference, and 5.0-volt reference circuits are used to connect the

TP sensors and the TAC module. The TP sensor 1 signal voltage increases as the throttle opens, from around 1.0 volt at 0 percent throttle to above 3.5 volts at 100 percent throttle. TP sensor 2 signal voltage decreases as the throttle is opened, from around 3.8 volts at 0 percent throttle to below 1.0 volt at 100 percent throttle.


The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually three individual APP sensors within one housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to connect the accelerator pedal sensor assembly and the Throttle Actuator Control (TAC) module. If only one APP sensor DTC is set, the redundant APP systems allow the TAC system to continue operating normally. This DTC sets if the Powertrain Control Module (PCM) detects a condition with more than one APP sensor. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. Two APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. However, if two or more DTCs are set involving more than one APP sensor, this DTC will set and the Reduced Engine Power message is displayed.


  • DTCs P1517 or P1518 are not set.
  • The ignition switch is in the crank or run position.
  • The ignition voltage is greater than 5.23 volts .


  • Two or more APP sensors are out of range or all three APP sensors disagree or one APP sensor is out of range and the other two APP sensors disagree.
  • All of the above conditions exist for less than 1 second .


  • 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 one of the following Reduced Engine Power modes:
  • The APP indicated angle is limited to a predetermined value to limit the amount of throttle control.


  • The APP indicated angle is limited to 0 percent . The control module only allows the engine to idle.


  • Under certain conditions the control module commands the engine OFF.
  • The message center displays Reduced Engine Power.


  • 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.
  • Use a scan tool in order to clear the MIL and the DTC.


  • Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
  • The APP sensor 1 and the TP sensor 1 5-volt reference circuits are internally connected within the TAC module.
  • The APP sensor 2 and the TP sensor 2 5-volt reference circuits are internally connected within the TAC module.
  • When the TAC module detects a condition within the TAC system more than 1 TAC system-related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.


Steps 1-2
The number below refers to the step number on the diagnostic table.


  1. When the problems are corrected which are causing the APP sensor DTCs to set, the status of this DTC will change to History.
Service and Repair


NOTE: Handle the electronic throttle control components carefully. Use cleanliness in order to prevent damage. Do not drop the electronic throttle control components. Do not roughly handle the electronic throttle control components. Do not immerse the electronic throttle control components in cleaning solvents of any type.


  1. An 8 digit part identification number is XXXXX on the throttle body casting. Refer to this number if servicing, or part replacement is required.
  2. Remove the air induction assembly. IMPORTANT: Cover or plug any openings when servicing the throttle body in order to prevent possible contamination.
  3. Disconnect the throttle actuator motor harness connector.
  4. Disconnect the throttle position (TP) sensor harness connector.
  5. Remove the throttle body attaching nuts. IMPORTANT: Do not reuse the throttle body gasket. Install a new gasket during assembly.
  6. Remove the throttle body and the gasket.
  7. Discard the throttle body gasket.



  1. Install a new throttle body gasket.
  2. Install the throttle body assembly. IMPORTANT: Always use a torque wrench in order to obtain the proper torque.
  3. Install the throttle body attaching nuts.
Tighten the throttle body nuts to 10 N.m (89 lb in) .

IMPORTANT: Ensure that the electrical connector to throttle body motor and the connector seal are properly installed and not damaged.

  1. Connect the TP sensor harness connector.
  2. Connect the throttle actuator motor harness connector.
  3. Install the air induction assembly.
  4. With the vehicle not in reduced engine power, turn ON the ignition with the engine OFF. Inspect for complete throttle opening and closing positions. Use a scan tool to monitor the throttle angles while operating the accelerator pedal to open and close the throttle. The accelerator pedal should operate freely without binding between full closed throttle and wide open throttle.
  5. Start the engine.
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