GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2003 🢒 Century 🢒 DTC 🢒 DTC P1121

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with three circuits:

    • A 5-volt reference circuit
    • A low reference circuit
    • A TP sensor signal circuit

The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the wide open throttle (WOT) position provides the PCM with a signal voltage from below 1.0 volt to greater than 4.0 volts through the TP sensor signal circuit. If the PCM detects an intermittent excessively high signal voltage, DTC P1121 sets.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The PCM detects that the TP sensor voltage is intermittently more than 4.9 volts.

Action Taken When the DTC Sets
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC
    • 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 non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Test Description

The number below refer to the step number on the diagnostic table:

  1. This test will determine an intermittent faulty TP sensor utilizing the DMMs MIN MAX, 100 millisecond capture mode.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Turn OFF the ignition.
  2. Disconnect the throttle position (TP) sensor electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground with a DMM.
  5. Lightly touch and move the related engine wiring harnesses and connectors for all 5-volt reference circuits while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Refer to Testing for Electrical Intermittents and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 3

3
  1. Measure the voltage from the signal circuit of the TP sensor to a good ground with a DMM.
  2. Lightly touch and move the related engine wiring harnesses and connectors while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Refer to Testing for Electrical Intermittents and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 4

4
  1. Measure the resistance from the low reference circuit of the TP sensor to a good ground with a DMM.
  2. Lightly touch and move the related engine wiring harnesses and connectors while observing resistance. Any change in resistance indicates the area where an open or high resistance may be found. Refer to Testing for Electrical Intermittents , Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 5

5

Test for poor connections at the TP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 6

6

Test for poor connections at the powertrain control module (PCM) harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Measure the resistance between the TP sensor signal terminal and the low reference terminal at the TP sensor using the MIN MAX function on the DMM.
  3. Slowly depress the accelerator pedal to the wide open throttle (WOT) position, then release the pedal back to the closed throttle position several times.

Did you observe a MAX value of infinite ohms or a MIN value of 0 ohms?

Go to Step 8

Go to Intermittent Conditions

8

Replace the TP sensor. Refer to Throttle Position Sensor Replacement .

Did you complete the replacement?

Go to Step 9

--

9
  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 10

10

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