GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P1121: Throttle Position (TP) Sensor Circuit Intermittent High Voltage

DTC P1122: Throttle Position (TP) Sensor Circuit Intermittent Low Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open

Short to Voltage

5-Volt Reference

P0122, P1122

P0122, P1122

P0123, P1121

Throttle Position Sensor Signal

P0122, P1122

P0122, P1122

P0123, P1121

Low Reference

--

P0123, P1121

--

Typical Scan Tool Data

TP Position Sensor

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: The engine is operating at idle.

Parameter Normal Range: TP Position Sensor 0%

5-Volt Reference

0%

0%

99%

Throttle Position Sensor Signal

0%

0%

99%

Low Reference

--

99%

--

Circuit/System Description

The throttle position (TP) sensor is used by the engine control module (ECM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with the following 3 circuits:

    • A 5-volt reference
    • A low reference
    • A signal

The ECM provides the TP sensor with 5 volts on the 5-volt reference circuit, and a ground on the low reference circuit. The TP sensor provides a signal voltage feedback that changes relative to throttle plate angle.

Conditions for Running

    • The ignition is ON or the engine is running.
    • The DTCs runs continuously when the above condition is met.

Conditions for Setting the DTC

P1121

The ECM detects that the TP sensor voltage is less than 0.3 volt intermittently.

P1122

The ECM detects that the TP sensor voltage is greater than 4.9 volts intermittently.

Action Taken When the DTC Sets

DTCs P1121 and P1122 are Type C DTCs.

Conditions for Clearing the MIL/DTC

DTCs P1121 and P1122 are Type C DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Engine running, observe the DTC Information with a scan tool. DTCs P0122 or P0123 should not set.
  2. If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  3. Observe the DTC Information with a scan tool. DTCs P1121 or P1122 should not set.
  4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Engine running, observe the scan tool throttle position (TP) sensor parameter while moving the related wiring harness and harness connectors. The reading should not change abruptly.

If the reading changes abruptly, repair the wiring harness and harness connectors.

Component Testing

  1. Ignition OFF, disconnect the harness connector at the TP sensor.
  2. Test for 1,160-1,175 ohms between the 5-volt reference terminal 2 and the low reference terminal 1.
  3. If not within the specified range, replace the TP sensor.
  4. Test the resistance between the signal terminal 3 and the low reference terminal 1. Sweep the TP sensor through the entire range. The resistance should vary between 1,530-630 ohms without any spikes or dropouts.
  5. If not within the specified range or is erratic, replace the TP sensor.
  6. Apply 5 volts and ground to the applicable terminals of the TP sensor, and measure the voltage between the signal terminal 3 and the low reference terminal 1. Sweep the TP sensor through the entire range. The voltage should vary between 4.3-0.6 volts without any spikes or dropouts.
  7. If not within the specified range or is erratic, replace the TP sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Throttle Position Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming