DTC P0121
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Joined: 26 Oct 2004
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PostPosted: Mon Apr 04, 2005 9:07 am    Post subject: DTC P0121 Reply with quote

DTC P0121

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is potentiometer sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor from the closed throttle position to the wide open throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. When the Conditions for Running this DTC are met, the PCM will use the manifold absolute pressure (MAP) sensor in order to determine if the predicted operating range of the TP sensor is correct. When the TP sensor voltage is out of this predicted range, this DTC sets.

DTC Descriptors

This diagnostic procedure supports the following DTC.

DTC P0121 Throttle Position (TP) Sensor Performance

Conditions for Running the DTC
  • DTCs P0106, P0107, P0108, P0122, P0123, P1122, and P1123 are not set.
  • The engine is operating for more than 10 seconds.
  • The engine coolant temperature is more than 0°C (32°F).
  • The idle air control (IAC) valve is between 0-255 counts.
  • The MAP is less than 55 kPa. OR
  • The MAP is more than 65 kPa.
  • The MAP is steady.
Conditions for Setting the DTC
  • The predicted throttle angle does not match the actual throttle angle.
  • The condition exists for 20 seconds.
Action Taken When the DTC Sets
  • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
  • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
  • A skewed MAP sensor may cause this DTC to set. If the TP sensor is operating properly, and if this DTC continues to set, test the MAP sensor for proper operation.
  • The PCM 5-volt reference circuits are internally connected within the PCM. If all the TP sensor circuits are OK, inspect the MAP sensor for malfunctions.
  • If DTC occurs intermittently, performing the DTC P1121 diagnostic test may isolate the cause of the fault. Refer to DTC P1121 .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step  2

Go to Diagnostic System Check - Engine Controls

2

Important:

If any other DTCs are set, diagnose those DTCs first.

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the TP sensor angle parameter on the scan tool while slowly opening the throttle to wide open throttle (WOT).
  • Closed throttle value is the first value.
  • Wide open throttle (WOT) value is above the second value.

Does the TP Angle increase steadily and evenly from the Closed Throttle value to above the Wide Open Throttle value?

0%

98%

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

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

Does the scan tool indicate TP sensor voltage at the specified value?

0 V

Go to Step 5

Go to Step 6

5

  1. Turn OFF the ignition.
  2. Connect a fused jumper wire between the 5-volt reference circuit and the signal circuit at the TP sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the TP sensor voltage parameter.

Does the scan tool indicate TP sensor voltage at the specified value?

5 V

Go to Step 9

Go to Step 7

6

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

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

7

Test the 5-volt reference circuit of the TP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step  15

Go to Step 8

8

Test the signal circuitof the TP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

9

Test the low reference circuit of the TP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 10

10

Test the 5-volt reference circuit of the TP sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

11

Test for an intermittent and for a poor connection at the TP sensor harness connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

12

Test for an intermittent and for a poor connection at the PCM harness connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step  15

Go to Step 14

13

Replace the TP sensor. Refer to Throttle Position (TP) Sensor Replacement .

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 16

16

Observe the Capture Info with a scan tool.

Are there any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK

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