GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 S10 Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P1121

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (PCM) in order to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits:

    • A 5-volt reference circuit
    • A low reference circuit
    • A signal 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 less than 1.0 volt to more than 4.0 volts through the signal circuit. If the PCM detects an intermittent and 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

The TP sensor intermittently indicates a throttle position signal of 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 refers to the step number on the diagnostic table.

  1. This test will determine an intermittent faulty TP sensor.

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
  1. Turn OFF the ignition.
  2. Disconnect the TP sensor.
  3. Connect a DMM between the 5-volt reference circuit and ground at the TP sensor harness connector .
  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 the 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
  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
  1. Turn the ignition OFF.
  2. Connect the 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 the resistance. Any change in the resistance indicates the area where an open or a 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 faulty 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 faulty 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 2 fused jumpers at the TP sensor, one at the signal terminal, and one at the 5-volt reference terminal.
  2. With the 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 at the DMM test leads.
  4. Press the MIN MAX button on the DMM.
  5. Slowly depress the accelerator pedal to 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 from the 5-volt reference terminal and connect the jumper to the low reference terminal.
  9. 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. 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