DTC P0121 Throttle Position (TP) Sensor Performance. Buick Riviera 1999

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1999 🢒 Riviera 🢒 DTC 🢒 DTC P0121 Throttle Position (TP) Sensor Performance

Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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 between 50 kPa and 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 or 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 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

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 .

•	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 .

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 P1121 Throttle Position (TP) Sensor Circuit Intermittent High Voltage diagnostic may isolate the cause of the fault.

Test Description

Number(s) below refer to the step number(s) 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 OBD Diagnostic 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.