P0121

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

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.

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 IP 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 consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

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 a scan tool.

DIAGNOSTIC AIDS
Check for the following conditions:
^ Skewed MAP signal or faulty MAP sensor - A skewed MAP signal may cause the PGM 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 MAP Sensor Circuit Diagnosis. Component Tests and General Diagnostics
^ Poor connection at PGM and IP sensor - Inspect harness connectors for the following conditions:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection

Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections, Connector Repairs and Connector Repairs in Diagrams.

^ 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 Diagrams.

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION
The number below refers to the step number on the diagnostic table:
12. 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.