GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1995 🢒 Cavalier 🢒 DTC 🢒 DTC P0121 Throttle Position (TP) Sensor Performance

Circuit Description

The powertrain control module (PCM) supplies a 5-volt reference signal and a ground to the sensor. the throttle position (TP) sensor sends a voltage signal back to the PCM relative to throttle blade opening. Voltage will vary from 0.45 volts at closed throttle to over 4.5 volts at wide open throttle.

Conditions for Setting
    • The manifold absolute pressure (MAP) sensor reads less than 22 kPa.
    • One or more of the following DTCs are not set; DTC P0107, DTC P0108, DTC P0122.
    • If the TP angle is greater than one of the following specified percentages at the given RPM:
       - TP angle is greater than 33 percent at 1,600 RPM.
       - TP angle is greater than 55 percent at 2,400 RPM.
       - TP angle is greater than 60 percent at 3,200 RPM.
       - TP angle is greater than 79 percent at 4,000 RPM.
       - TP angle is greater than 75 percent at 4,800 RPM.
       - TP angle is greater than 99 percent at 5,600 RPM.
    • The PCM detects 50 out of range samples out of 100.

Action Taken
    • The malfunction indicator lamp (MIL) will illuminate after two consecutive drive cycles with the fault active.
    • The TP angle will default to 0 percent when the vehicle speed is less than 2 mph and 10 percent when the vehicle speed is greater than 2 mph. The scan tool will display the defaulted value.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after passing three consecutive diagnostic tests.
    • A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault.
    • History and current DTCs can be cleared by using a scan tool.

Diagnostic Aids

If a DTC P0121 cannot be duplicated, the information included in the Freeze Frame data can be useful. Use the Freeze Frame data to determine how many ignition cycles have passed since last set. If the DTC occurs intermittently, use the DTC P1121 diagnostic chart to help isolate the problem.

Test Description

The number below refers to the step number on the diagnostic table.

  1. The TP sensor has an auto zeroing feature. If the voltage reading is between 0.2-0.9 volts, the PCM will assume the TP sensor is at a closed throttle position. If the reading is out of the auto zeroing range at closed throttle look for a binding or damaged linkage.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Was the On-Board Diagnostic (OBD) System Check perform?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Ignition ON, engine OFF.
  2. Install a scan tool.
  3. Select the TP angle parameter on the scan tool.
  4. Monitor the scan tool while depressing the accelerator pedal to the floor and then slowly release the pedal. Repeat the procedure several times.

Does the TP angle value increase steadily when the accelerator pedal is depressed to the specified value and decrease steadily when the pedal is released to the specified value?

>95%

<2%

Go to Diagnostic Aids

Go to Step 3

3
  1. Disconnect the TP sensor electrical connector.
  2. Select the TP sensor on the scan tool.

Is the TP sensor voltage less than the specified value?

0.5 V

Go to Step 4

Go to Step 5

4
  1. Connect a test light between the 5-volt reference circuit and the TP sensor signal circuit at the TP sensor harness connector.
  2. Monitor the TP sensor voltage on the scan tool.

Is the TP sensor voltage greater than the specified value?

4.5 V

Go to Step 7

Go to Step 6

5
  1. Inspect the following items:
    2. • The TP sensor signal circuit for a short to voltage
    • The TP sensor ground circuit for high resistance between the TP sensor and the PCM
    • The TP sensor electrical connector for proper mating
  2. Repair any problem found.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 8

6
  1. Inspect the following items:
    2. • The TP sensor electrical connector for proper mating
    • The TP sensor circuit for high resistance between the TP sensor and the PCM.
  2. Repair any problem found.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 8

7

Replace the TP sensor.

Is the action complete?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

8

Replace the PCM.

Is the action complete?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

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