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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Savana 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 DTC P0121

Circuit Description

The throttle position (TP) sensor is a potentiometer.

The powertrain control module (PCM) supplies the TP sensor:

  1. a reference voltage
  2. a signal
  3. low reference circuits

When the throttle is depressed, the TP sensor signal rises to near the reference voltage. When the throttle is released, the TP sensor signal decreases from the reference voltage. The control module monitors the TP sensor signal circuit voltage in order to determine the throttle blade angle, or openin

This diagnostic trouble code (DTC) determines if the throttle position (TP) sensor signal input to the powertrain control module (PCM) does not closely match what the predicted value for the TP sensor should be. The PCM calculates what the TP signal voltage should be based on engine RPM. If the TP sensor voltage and the predicted TP sensor values do not closely match, this DTC will be set.

Conditions for Running the DTC
    • DTCs P0112, P0113, P0122, P0506, or P0507 are not set.
    • The engine is running.
    • The barometric pressure (BARO) is not in default.
    • The throttle position is steady.

Conditions for Setting the DTC

Stuck High Test

The TP is more than the calculated throttle position for more than 5 seconds.

Stuck Low Test

The TP is less than the calculated throttle position for more than 5 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

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.

Diagnostic Aids

The scan tool displays theTPin volts. The scan tool should display about 0.45-0.85 volts with the throttle closed and the ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward wide open throttle (WOT).

The scan tool will read the throttle angle percentage. 0 percent equals closed throttle. 100 percent equals WOT.

Inspect the condition of the connector and the sensor terminals for moisture or corrosion, and clean or replace the terminals as necessary. If corrosion is found, inspect the condition of the connector seal and repair or replace the seal as necessary. If DTC P0121 is intermittent, refer to Intermittent Conditions .

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

DTC P0121 TP Sensor System Performance

Step

Action

Values

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

Important: : If any other DTCs are set, diagnose those DTCs first.

  1. Turn ON the ignition with the engine OFF.
  2. Observe the TP sensor angle parameter on the scan tool while slowly opening the throttle to wide open throttle WOT.
    • Closed throttle value is the first value.
    • WOT value is above the second value.

Does the TP Angle increase steadily and evenly from the Closed Throttle value to above the WOT value?

0%

98%

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the TP sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the TP sensor voltage parameter.

Does the scan tool indicate TP sensor voltage at the specified value?

0 V

Go to Step 5

Go to Step 6

5
  1. Turn OFF the ignition.
  2. Connect a fused jumper wire between the 5-volt reference circuit and the signal circuit at the TP sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the TP sensor voltage parameter.

Does the scan tool indicate TP sensor voltage at the specified value?

5 V

Go to Step 9

Go to Step 7

6

With a DMM, test the TP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

7

With a DMM, test the TP sensor 5-volt reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step  15

Go to Step 8

8

Test the TP sensor signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

9

Test the TP sensor low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 10

10

Test the TP sensor 5-volt reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

11

Inspect for a poor connection 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 15

Go to Step 13

12

Inspect for a poor connection 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  15

Go to Step 14

13

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

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15
  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 16

Go to Step 2

16

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