GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 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; 5-volt reference, low reference, and signal. 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, This diagnostic trouble code (DTC) will set.

Conditions for Running the DTC
    • The ignition is ON.
    • DTCs P1635 or P1639 are not set.

Conditions for Setting the DTC

TP sensor intermittently indicates a throttle position signal 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.

DTC P1121 Throttle Position (TP) Sensor Intermittent High Voltage

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Test all 5-volt reference circuits for an intermittent short to voltage.

  1. Turn OFF the ignition.
  2. Disconnect the TP sensor.
  3. Connect a DMM between the TP sensor 5-volt reference circuit at the TP sensor harness connector and ground.
  4. Turn ON the Ignition, with the engine OFF.
  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 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 3

3

Test the TP sensor signal circuit for an intermittent short to voltage.

  1. Turn OFF the ignition.
  2. Connect a DMM between the TP sensor signal circuit at the TP sensor harness connector and ground.
  3. Turn ON the ignition, with the engine OFF.
  4. 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 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 4

4

Test the TP sensor low reference circuit for an intermittent open or high resistance.

  1. Turn OFF the ignition for 30 seconds.
  2. Connect a DMM between the TP sensor low reference circuit at the TP sensor harness connector and ground.
  3. 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 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

Inspect 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

Inspect for poor connections at the 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. Connect two jumper wires at the TP sensor, one at the signal terminal, and one at the 5-volt reference terminal.
  2. With a DMM set to the 40k ohms scale, connect the DMM to the jumper wires.
  3. Ensure a good, proper connection at the TP sensor and DMM test leads.
  4. Press the MIN MAX button on the DMM.
  5. Slowly depress the accelerator pedal to wide open throttle (WOT) and back to the closed throttle position several times.
  6. Press the MIN MAX button and record the MAX reading.
  7. Press the MIN MAX button again and record the MIN reading.
  8. Remove the jumper wire at the 5-volt reference terminal and connect it to the low reference terminal and repeat steps 2 through 7.

Did you record a MAX value of OL or record a MIN value of 0 ohms in either test?

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. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 10

Go to Step 2

10

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK