DTC P0121 Throttle Position (TP) Sensor Performance. Pontiac Grand Prix 2000

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2000 🢒 Grand Prix 🢒 Body and Accessories 🢒 Wiring Systems 🢒 DTC P0121 Throttle Position (TP) Sensor Performance

Refer to Engine Control Schematic

A/C Refrigerant Pressure Sensor, TP, MAP, ECT and IAT Sensor

Handling ESD Sensitive Parts Notice
Fuel Tank
Handling ESD Sensitive Parts Notice
Engine Controls Components
Powertrain Control Module Description
HO2S #1 and HO2S #2
Fuel Injectors
OBD II Symbol Description Notice
.

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 when MAP is between 50 kPa and 70 kPa.

Conditions for Running the DTC

•	No active TP sensor circuit or MAP sensor DTC.

•	The engine is running for longer than 2 minutes.

•	The ECT sensor temperature above 75°C (167° F).

•	The MAP reading is below 50 kPa for a TP sensor skewed high.

•	The MAP reading is above 70 kPa for a TP sensor skewed low.

•	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.

•	The 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/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

Inspect 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. Monitor the scan tool 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

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

•	Loose terminal connection

-	Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

•

Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

•	Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Test Description

The number below refers to the step number on the diagnostic table:

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.

DTC P0121 - TP System Performance

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Important: If any other DTCs are set, diagnose the other DTCs first.

Turn ON the ignition, with the engine OFF.
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?

•	Closed throttle value is the first value.

•	Wide open throttle value is the second value.

100%

Go to Diagnostic Aids

Go to Step 3

Turn OFF the ignition.
Disconnect the TP sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP voltage parameter.

Does the scan tool indicate that the TP voltage parameter is near the specified value?

Go to Step 4

Go to Step 5

Turn OFF the ignition.
Connect a 3 amp fused jumper wire between the 5 volt reference circuit of the TP sensor and the signal circuit of the TP sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP voltage parameter.

Does the scan tool indicate that the TP voltage parameter is at the specified value?

Go to Step 8

Go to Step 6

Test the signal circuit of the TP sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems.