For 1990-2009 cars

### 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 P0121: Throttle Position (TP) Sensor 1 Performance
DTC P0122: Throttle Position (TP) Sensor 1 Circuit Low Voltage
DTC P0123: Throttle Position (TP) Sensor 1 Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
TP Sensor 1 Signal | P0122 | P0121 | P0122 | P0123 | --
TP Sensor 5-Volt Reference | P0122 | P0121 | P0122 | P0123 | --
TP Sensor Low Reference | -- | P0121 | P0123 | -- | --

### Typical Scan Tool Data

#### TP Sensor 1

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Parameter Normal Range: 4.63-0.18 V
TP Sensor 1 Signal | 0 V | 0 V | 5 V
TP Sensor 5-Volt Reference | 0 V | 0 V | 5 V
TP Sensor Low Reference | -- | 5 V | --

### Circuit/System Description

The throttle body assembly contains 2 throttle position (TP) sensors. The TP sensors are mounted to the throttle body assembly and are not serviceable. The TP sensors provide a signal voltage that changes relative to throttle blade angle. The engine control module (ECM) supplies the TP sensors with a common 5-volt reference circuit, a common low reference circuit, and 2 independent signal circuits.

The TP sensors have opposite functionality. TP sensor 1 signal voltage decreases from above 4 volts at idle to below 1 volt at wide open throttle (WOT). TP sensor 2 signal voltage increases from below 1 volt at idle to above 4 volts at wide open throttle.

The ECM compares the signal of the TP sensor 1 and TP sensor 2 through the entire range. If the ECM detects a predetermined difference between sensor 1 and sensor 2, or a predetermined difference from the predicted range, this DTC sets.

### Conditions for Running the DTC

• | The system voltage is more than 7 volts.

• | The TP sensor 1 voltage is between 0.18-4.63 volts.

• | DTC P0121 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

#### P0121

• | The TP sensor 1 disagrees more than 6.3 percent from TP sensor 2 for over 140 ms.

• | The TP sensor 1 disagrees more than 9 percent from the throttle position calculated from mass air flow (MAF) signal for over 280 ms.

#### P0122

The TP sensor 1 voltage is less than 0.18 volt for over 140 ms.

#### P0123

The TP sensor 1 voltage is more than 4.63 volts for over 140 ms.

### Action Taken When the DTC Sets

• | DTC P0121 is a type B DTC.

• | DTC P0122 and P0123 are type A DTCs.

• | The control module commands the TAC system to operate in the Reduced Engine Power mode.

• | A message center or an indicator displays Reduced Engine Power.

### Conditions for Clearing the DTC

• | DTC P0121 is a type B DTC.

• | DTC P0122 and P0123 are type A DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module 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

Scan Tool Data List

### Circuit/System Verification

1. Ignition ON, observe the TP sensor 1 voltage parameter. The reading should be between 0.18-4.63 volts and change with accelerator pedal input.
2. Observe the TP sensor 1 and 2 parameter. The scan tool should indicate agreement.
3. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.

⇒ | If DTC P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, or P0699 are set, refer to DTC P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 .

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the throttle body. Allow sufficient time for the ECM to completely power down.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal C and ground.

⇒ | If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.

⇒ | If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒ | If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.

⇒ | If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit terminal E of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.

⇒ | If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

6. Ignition OFF, disconnect the harness connector at the ECM.
7. Test for less than 5 ohms of resistance on the TP sensor circuits between the following terminals:

• | ECM C1 5-volt reference circuit terminal 39 to terminal E.

• | ECM C1 signal circuit terminal 90 to terminal D.

⇒ | If greater than 5 ohms, repair the affected circuit.

8. Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor 2 signal circuit terminal F.

⇒ | If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit.

9. If all circuits test normal, replace the throttle body.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for ECM replacement, setup, and programming

• | Throttle Body Assembly Replacement