Refer to Engine Controls Schematics
Cell 21: Engine Data Sensors
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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 and 70 kPa.
Conditions for Running the DTC
| • | No active TP, 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 second consecuitive trip in which the diagnostic has been run and failed. |
| • | If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been 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 the 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. This condition can cause DTC P0121 to be set. Refer to Manifold Absolute Pressure Sensor Circuit Diagnosis . |
| • | 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 Intermittents and Poor Connections Diagnosis 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 Fail 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 P1122 Throttle Position (TP) Sensor Circuit Intermittent Low Voltage diagnostic may isolate the cause of the fault.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table:
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An incorrect MAP signal may cause the PCM to incorrectly calculate the predicted TP sensor value during high engine load situations. Test for an unusually low MAP reading. This condition can cause DTC P0121 to be set.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain OBD System Check performed? | -- | ||||||
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?
| -- | Go to Diagnsotic Aids | |||||
3 |
Does the scan tool indicate that the TP Sensor voltage is equal to the the specified value? | 0.0V | ||||||
4 |
Does the scan tool indicate that the TP Sensor voltage is equal to the the specified value? | 5.0V | ||||||
5 | Test the TP Sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||||||
6 | Using J 39200 DMM measure the voltage between 5 Volt Reference A circuit and a known good ground at the TP Sensor harness connector. Does the voltage measure less than the specified value? | -- | ||||||
7 | Test the 5 Volt Reference A Circuit for high resistance between TP Sensor and PCM, or a poor connection at the PCM. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||||||
8 | Test the TP Sensor Signal Circuit for high resistance between TP Sensor and PCM, or a poor connection at the PCM. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||||||
9 | Test the TP Sensor Ground Circuit for high resistance between TP Sensor and PCM, or a poor connection at the PCM. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs . Was a problem found? | -- | ||||||
10 | Inspect for poor and intermittent connections at the TP Sensor Harness Connector. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , Connector Repairs , and Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||||||
11 | Replace the TP sensor. Refer to TP Sensor Replacement . Is the action complete? | -- | -- | |||||
|
Important: : Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | ||||||
13 |
Does scan tool indicate DTC P0121 failed this ignition? | -- | System OK |
