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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 2WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage

Object Number: 50793 Size: SF
Engine Controls Components
Cell 20: MAP, IAT, TPS and ECT Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Powertrain Control Module (PCM) supplies a 5.0 volt reference signal and a ground to the sensor. The TP sensor sends a voltage signal back to the PCM relative to the throttle plate opening. The voltage will vary from approximately 0.35 volt at closed throttle, to over 4.65 volts at wide open throttle (WOT).

Conditions For Running The DTC

The engine is running.

Conditions for Setting the DTC

The TP sensor reads less than 0.20V for 6.25 seconds.

Action Taken When the DTC Sets
    • The Malfunction Indicator Lamp (MIL) illuminates after two consecutive igntion cycles with the malfunction present.
    • The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers stores this information.
    • A history DTC is stored.
    • The TP angle will default to 0% when the vehicle speed is less than 2 mph. The TP angle defaults to 10% when the vehicle speed is more than 2 mph. The scan tool shows the defaulted value.

Conditions for Clearing the MIL/DTC
    • The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
    • A history DTC will clear after 40 consecutive warm up cycles without a fault.
    • Use a scan tool to clear the DTCs.

Diagnostic Aids

If a DTC P0122 cannot be duplicated, the information included in the Freeze Frame data can be useful. Use the scan tool DTC information data in order to determine the status of the DTC. If the DTC occurs intermittently, use the DTC P0105 Diagnostic table in order to help isolate the problem.

Test Description

The number(s) below refer(s) to the step number(s) on the Diagnostic Table.

  1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

    2.

  2. The TP sensor has an auto zeroing feature. If the voltage reading is between 0.20 Volts and 0.90 Volts, the PCM will automatically assume this as a closed throttle position (0 percent).

    3.

  3. This simulates a DTC P0123. If the PCM recognizes the high voltage signal, this indicates that the PCM and the wiring are OK.

    4.

  4. This simulates a high voltage signal which will identify an open in the signal circuit.

    5.

  5. Important: The Powertrain Control Module (PCM) uses a single internal 5.0 volt power supply to supply power to all the engine control components. If one component shorts its 5.0 volt reference circuit to ground or battery voltage, the other 5.0 volt reference circuits will also have a low or high voltage.

    If any additional DTCs are set, check the 5.0 Volt reference circuits for a short to ground.

    6.

  6. If the test light illuminates while probing the TP signal circuit terminal in step 5, then the TP signal circuit is shorted to ground.

    7.

  7. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and the Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.

DTC P0122-Throttle Position (TP) Sensor Circuit Low Voltage

Step

Action

Value(s)

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

  1. Turn ON the ignition switch leaving the engine OFF.
  2. Install a scan tool.

Is the TP sensor voltage below the specified value?

0.2 V

Go to Step 4

Go to Step 3

3
  1. Review the Freeze Frame data and record the parameters.
  2. Start the engine.
  3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting the DTC as specified.

Is the TP sensor voltage below the specified value?

0.2 V

Go to Step 4

Go to Step 12

4

  1. Turn OFF the ignition switch.
  2. Disconnect the TP sensor electrical connector.
  3. Connect a jumper wire between the following circuit terminals in the TP sensor electrical connector:
    4. • 5.0 Volt reference circuit terminal
    • TP sensor signal circuit terminal
  4. Turn ON the ignition switch leaving the engine OFF.

Is the TP sensor voltage greater than the specified value?

4.0 V

Go to Step 10

Go to Step 5

5

Connect a test light between the following circuit terminal at the TP sensor electrical connector.

    • Battery terminal
    • TP sensor signal circuit terminal

Is the TP sensor voltage greater than the specified value?

4.0 V

Go to Step 6

Go to Step 8

6

Important: The Powertrain Control Module (PCM) uses a single internal 5.0 volt power supply to supply power to all the engine control components. If one component shorts its 5.0 volt reference circuit to ground or battery voltage, the other 5.0 volt reference circuits will also have a low or high voltage.

  1. Turn OFF the ignition switch.
  2. Check for the following conditions in the 5.0 V reference:
    3. • Open circuit
    • Short to ground
  3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 7

7
  1. Check the 5.0 V reference circuit for a poor electrical connection terminal(s) at the PCM electrical connector.
  2. Replace the terminal(s) as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 11

8

  1. Turn OFF the ignition switch.
  2. Check for the following conditions in the TP sensor signal circuit:
    3. • Open circuit
    • Short to ground
  3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 9

9
  1. Check the TP sensor signal circuit for a poor electrical connection at the PCM electrical connector.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 12

Go to Step 11

10
  1. Turn OFF the ignition switch.
  2. Check the TP sensor electrical connector for a poor electrical connection.
  3. If the TP sensor electrical connection is not malfunctioning, replace the TP sensor. Refer to the Throttle Position Sensor Replacement .

Is the action complete?

--

Go to Step 12

--

11

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

Is the action complete?

--

Go to Step 12

--

12
  1. Clear the DTCs with the scan tool.
  2. Start the engine.
  3. Idle the engine at the normal operating temperature.
  4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan indicate that this diagnostic ran and passed?

--

Go to Step 13

Go to Step 2

13

Check to see if any additional DTCs are set.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to applicable DTC table

System OK