Circuit Description
The throttle position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from below 1.0 volt at closed throttle to above 4.0 volts at wide open throttle (WOT).
When the MAP reading is below 50 kPa the diagnostic checks for a skewed high TP sensor. When the MAP reading is above 70 kPa the diagnostic checks for a skewed low TP sensor. If the PCM detects an out of range condition, DTC P0121 will be set. The diagnostic will not run between 50 kPa-70 kPa.
Conditions for Running the DTC
| • | No active TP sensor circuit or MAP sensor DTC. |
| • | The engine is running. |
| • | The ECT sensor temperature above 70°C (158°F). |
| • | The MAP reading is below 50 kPa. |
| • | The MAP reading is above 70 kPa. |
| • | The MAP steady for 5 seconds or more. |
Conditions for Setting the DTC
| • | The TP sensor reading is above the predicted value when the MAP is below 50 kPa. |
| • | The TP sensor reading is below the predicted value when the MAP is above 70 kPa. |
| • | Above conditions are present for 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic runs and fails. |
| • | If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Skewed MAP signal or faulty MAP sensor. |
| A skewed MAP signal may cause the PCM to incorrectly determine the TP sensor is out of range. Check for an unusually low or high MAP reading. Refer to Manifold Absolute Pressure Sensor Circuit Diagnosis . This condition can cause DTC P0121 to be set. |
| • | Poor connection at PCM and TP sensor. |
| Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Repairing Connector Terminals and Connector Repairs in Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the TP sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
If DTC P0121 cannot be duplicated, the information included in the Failure Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1121 Throttle Position (TP) Sensor Circuit Intermittent High Voltage diagnostic may isolate the cause of the fault.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
2 |
Important: If any other DTCs are set, diagnose the other DTCs first.
Does TP angle increase steadily and evenly from the closed throttle value to the wide open throttle value?
| 0 percent 100 percent | Go to Diagnostic Aids | |||||
3 |
Does the scan tool indicate that the TP voltage parameter is near the specified value? | 0V | ||||||
4 |
Does the scan tool indicate that the TP voltage parameter is near the specified value? | 5V | ||||||
5 | Test the signal circuit of the TP sensor for a short to voltage. Refer to Measuring Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
6 | Test the 5 volt reference circuit of the TP sensor for high resistance, or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | |||||||
7 | Test the signal circuit of the TP sensor for high resistance, or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | |||||||
8 | Test the ground circuit of the TP sensor for high resistance, or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
9 | Inspect for poor connections at the harness connector of the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | |||||||
10 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | ||||||
11 |
Important: Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | ||||||
Does the scan tool indicate DTC P0121 failed this ignition? | -- | System OK |
