DTC P0121 Throttle Position (TP) Sensor Performance. Buick GL7 (Export) 2000

For 1990-2009 cars

### Circuit Description

The throttle position (TP) sensor circuit provides a voltage signal that changes relative to the throttle blade angle. The signal voltage will vary from less than 1.0 volt at closed throttle to more than 4.0 volts at wide open throttle (WOT).

When the manifold absolute pressure (MAP) reading is less than 50 kPa (7.3 psi) the diagnostic checks for a skewed-high TP sensor. When the MAP reading is more than 70 kPa (10.2 psi) 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 (7.3 psi) and 70 kPa (10.2 psi).

### Conditions for Running the DTC

• | No active TP sensor circuit or MAP sensor DTCs.

• | The engine has been running for at least 120 seconds.

• | The ECT sensor temperature is more than 75°C (167° F).

• | The MAP reading is less than 50 kPa (7.3 psi).

• | The MAP reading is more than 70 kPa (10.2 psi).

• | The MAP is steady for 5 seconds or more.

### Conditions for Setting the DTC

• | The TP sensor reading is more than the predicted value when the MAP is less than 50 kPa (7.3 psi).

• | The TP sensor reading is less than the predicted value when the MAP is more than 70 kPa (10.2 psi).

• | 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 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

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. Check for an unusually low or high MAP reading. This condition can cause DTC P0121 to be set. Refer to DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage .

• | A poor connection at the PCM or the TP sensor. Inspect the harness connectors for the following conditions:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal-to-wire connections

• | Use a corresponding mating terminal to test for proper tension.

• | Refer to Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals and Connector Repairs in Wiring Systems

• | A 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 the connectors and the 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 Failure Records data can be useful in determining the 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

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

1. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.

#### DTC P0121 - TP System Performance

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

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

1. Turn ON the ignition, leaving the engine OFF.
2. Observe the TP Angle reading on the scan tool while slowly opening the throttle.

Does the TP Angle increase steadily and evenly from the closed throttle value to the wide open throttle value?

• | The closed throttle value is the first value.

• | The wide open throttle value is the second value.

0%

100%

Go to Diagnostic Aids

Go to Step 3

3

1. Turn OFF the ignition.
2. Disconnect the TP sensor.
3. Turn ON the ignition, leaving the engine OFF.
4. With a scan tool, observe the TP voltage parameter.

Is the TP voltage near the specified value?

0 V

Go to Step 4

Go to Step 5

4

1. Turn OFF the ignition.
2. 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.
3. Turn ON the ignition, leaving the engine OFF.
4. With a scan tool, observe the TP voltage parameter.

Does the TP voltage equal the specified value?

5 V

Go to Step 8

Go to Step 6

5 | Test the signal circuit of the TP sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11
6 | Test the 5 volt reference circuit of the TP sensor for high resistance or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7
7 | Test the signal circuit of the TP sensor for high resistance or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11
8 | Test the ground circuit of the TP sensor for high resistance or a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9
9 | Inspect for poor connections at the harness connector of the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10
10 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
11 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 12 | --

12

1. Review and record the scan tool Failure Records data.
2. Clear the DTCs.
3. Operate the vehicle within the Failure Records conditions as noted.
4. Using a scan tool, monitor the Specific DTC info for DTC P0121.

Does the scan tool indicate DTC P0121 failed this ignition?

--

Go to Step 2

System OK