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. An incorrect MAP signal may cause the PCM to incorrectly calculate the predicted TP sensor value during high engine load situations. Check for an unusually low MAP reading. This condition can cause DTC P0121 to be set. |
| • | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT 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. |
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 and DTC P1121 Diagnostic Charts 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. Check 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? | -- | ||||||
Is MAP reading less than the specified value? | 55 kPa | |||||||
3 |
Is the MAP reading Greater than the specified value? | 95 kPa | ||||||
4 |
Was the MAP signal circuit open or shorted? | -- | ||||||
5 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | -- | |||||
6 | Observe the TP Angle reading on the scan tool while slowly opening the throttle. Does TP Angle increase steadily and evenly from the closed throttle value to the wide open throttle value?
| 0% 100% | Go to Diagnostic Aids | |||||
7 |
Is the TP sensor reading near the specified value? | 0.0V | ||||||
8 |
Is the TP sensor reading at the specified value? | 5.0V | ||||||
9 | Check the following items:
Was a problem found? | -- | ||||||
10 | Check the following items:
Was a problem found? | -- | ||||||
11 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | -- | |||||
Replace the PCM. Important: : Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . | -- | -- | ||||||
13 |
Does scan tool indicate DTC P0121 failed this ignition? | -- | Repair complete |
