DTC P0121. Generic Unit Repair 2002

For 1990-2009 cars only

Makes 🢒 Generic 🢒 2002 🢒 Unit Repair 🢒 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 a reference voltage, a signal, and 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 opening.

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

•	BARO not in default

•	The throttle position is steady

Conditions for Setting the DTC

Stuck High Test

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

Stuck Low Test

The throttle position 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 the throttle position in volts. The scan tool should display about 0.45 volts to 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 wide open throttle (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 Symptoms - Engine Controls.

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

•	A poor connections

•	Rubbed through wire insulation

•	A broken wire inside the insulation

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

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

Test Description

The numbers below refer to the step numbers on the diagnostic table.

The TP sensor has an auto zeroing feature. If the voltage reading is within the range of about 0.2-0.9 volt, the PCM uses that value as a closed throttle. If the reading is out of the auto zero range at the closed throttle, check for a binding throttle shaft or a damaged linkage. If the throttle shaft and the linkage are okay, continue with the diagnosis.

The TP sensor throttle angle should range smoothly from 0-100 percent when the throttle is slowly depressed to the wide open throttle (WOT) position. If not, a skewed out of range TP sensor, low reference voltage or a poor connection could be possible causes.

With the TP sensor disconnected, the TP sensor signal voltage should go low if the PCM and the wiring are okay and a DTC P0122 may set.

Reference voltage less than 4.5 volts could cause a poor TP performance condition. Be sure to check both 5 volt reference circuits for conditions that could cause low voltage on the TP sensor circuit.

The throttle shaft, throttle linkage or accelerator cable not closing due to sticking or binding could cause a TP sensor poor performance condition.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame/Failure Records for reference. The control modules data is deleted once the Clear Info function is used.

Did you perform the Diagnostic System Check-Engine Controls ?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Install the scan tool.
Turn ON the ignition, with the engine OFF.

Does the scan tool display the throttle angle more than the specified value?

Go to Step 6

Go to Step 3

Important: The engine must remain OFF for this step.

Depress the throttle slowly to wide open throttle (WOT) while watching the throttle angle increase through the specified range.

Does the TP sensor range reach the maximum specified value?

0-100%

Go to Step 4

Go to Step 10

Release the throttle.

Does the scan tool display the throttle angle more than the specified value?

Go to Step 6

Go to Step 5

The DTC is intermittent.

Are any additional DTCs set?

Go to Diagnostic Trouble Code (DTC) List

Go to Diagnostic Aids

Disconnect the TP sensor harness connector.

Does the scan tool display the TP sensor at the specified value?

0 V

Go to Step 7

Go to Step 9

Turn OFF the ignition.
Probe the TP sensor ground circuit with a test lamp connected to B+.

Is the test lamp ON?

Go to Step 8

Go to Step 14

Turn ON the ignition, with the engine OFF.
Probe the TP sensor 5 volt reference circuit at the TP sensor harness connector with a DMM connected to a ground.

Is the voltage more than the specified value?

5.2 V

Go to Step 15

Go to Step 19

Turn OFF the ignition.
Disconnect the PCM C2 connector.
Turn ON the ignition, with the engine OFF.
Probe the TP sensor signal circuit at the TP sensor harness connector with a DMM connected to a ground.

Is the voltage more than the specified value?

0 V

Go to Step 13

Go to Step 22

Turn OFF the ignition.
Disconnect the TP sensor harness connector.
Jumper the TP sensor 5 volt reference circuit to the TP sensor signal circuit at the TP sensor harness connector.
Turn ON the ignition, with the engine OFF.

Does the scan tool display the throttle angle at the specified value?

100%

Go to Step 17

Go to Step 11

Turn ON the ignition, with the engine OFF
Probe the TP sensor 5 volt reference circuit with a DMM connected to a ground.

Is the voltage near the specified value?

5.2 V

Go to Step 12

Go to Step 16

Turn OFF the ignition.
Disconnect the PCM C2 connector.
Check the resistance in the TP sensor signal circuit between the TP sensor harness connector and the PCM connector with a DMM.

Is the resistance near the specified value?

0ohms

Go to Step 22

Go to Step 18

Repair the short to voltage on the TP sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Repair the open in the TP sensor ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Repair the short to voltage in the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Repair the low voltage condition on the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Check for a poor connection at the TP sensor.

Did you find a problem?

Go to Step 18

Go to Step 19

Repair the circuit as necessary. Refer toWiring Repairs orConnector Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Check the throttle shaft, linkage, throttle and cruise cables for the following conditions:

•

Binding

•

Sticking

Did you find a problem?

Go to Step 20

Go to Step 21

Repair the throttle shaft, linkage, or cables as necessary.

Is the action complete?

Go to Step 24

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

Is the action complete?

Go to Step 24

Check for a poor connection at the PCM. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find a problem?

Go to Step 24

Go to Step 23

Replace the PCM. Refer to Powertrain Control Module Replacement .
Perform the Passlock Reprogramming Procedure. Refer to PASSLOCK Reprogramming Seed and Key in Theft Deterrent.
Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

Go to Step 24

Using the scan tool, clear the DTCs.
Start the engine.
Allow the engine to idle until the engine reaches normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number that was set.
Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

Go to Step 25

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to Diagnostic Trouble Code (DTC) List

System OK