Circuit Description
The throttle position (TP) sensor is a potentiometer. The control module supplies the TP sensor a reference voltage, a signal, and ground 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 TP sensor signal input to the vehicle control module (VCM) does not closely match what the predicted value for the TP sensor should be. The VCM 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
| • | No active manifold absolute pressure (MAP) DTCs |
| • | The engine is running. |
| • | BARO is not in default |
| • | The throttle position is steady. |
Stuck High Test
The MAP is less than 50 kPa.
Stuck Low Test
| • | The Stuck High Test has passed. |
| • | The MAP is more than 60 kPa. |
| • | The idle air control (IAC) is between 10-340 counts. |
Conditions for Setting the DTC
Stuck High Test
The throttle position value is more than the predicted throttle position value based on engine RPM for more than 25 seconds.
Stuck Low Test
The throttle position value is less than the predicted throttle position value based on engine RPM for more than 25 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
The scan tool displays the throttle position in volts. It should display between 0.45 volts and 0.85 volts with the throttle closed and ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward the wide open throttle (WOT) position.
Also, the scan tool displays the throttle angle percentage. Zero percent equals closed throttle. One hundred percent equals wide open throttle (WOT).
A MAP related DTC could set if the TP throttle angle is skewed or stuck at a value of less than 20 percent.
Check the condition of the connector and sensor terminals for moisture or corrosion, and clean or replace the terminals as necessary. If corrosion is found, check the condition of the connector seal and repair or replace as necessary. If DTC P0121 is intermittent, refer to Symptoms .
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.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The TP sensor has an auto zeroing feature. If the voltage reading is within the range of about 0.2-0.9 volt, the VCM 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.
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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.
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With the TP sensor disconnected, the TP sensor signal voltage should go low if the VCM and the wiring are okay and a DTC P0122 may set.
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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 | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
Does the scan tool display the throttle angle more than the specified value? | 2% | |||||||
|
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% | |||||||
4 | Release the throttle. Does the scan tool display the throttle angle more than the specified value? | 2% | ||||||
5 | The DTC is intermittent. Are any additional DTCs set? | -- | Go to the applicable DTC table | Go to Diagnostic Aids | ||||
Disconnect the TP sensor harness connector. Does the scan tool display the TP sensor at the specified value? | 0 V | |||||||
7 |
Is the test lamp ON? | -- | ||||||
8 |
Is the voltage more than the specified value? | 5.2 V | ||||||
9 |
Is the voltage more than the specified value? | 0 V | ||||||
10 |
Does the scan tool display the throttle angle at the specified value? | 100% | ||||||
11 |
Is the voltage near the specified value? | 5.2 V | ||||||
12 |
Is the resistance near the specified value? | 0ohms | ||||||
13 | Repair the short to voltage on the TP sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
14 | Repair the open in the TP sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
15 | Repair the short to voltage in the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
Repair the low voltage condition on the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||||||
17 | Check for a poor connection at the TP sensor. Did you find a problem? | -- | ||||||
18 | Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
Check the throttle shaft, linkage, throttle, and cruise cables for the following conditions:
Did you find a problem? | -- | |||||||
20 | Repair the throttle shaft, linkage, or cables as necessary. Is the action complete? | -- | -- | |||||
21 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | -- | |||||
22 |
Did you find a problem? | -- | ||||||
23 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |||||
24 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||
25 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
