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 P0122: Throttle Position (TP) Sensor Circuit Low Voltage
DTC P0123: Throttle Position (TP) Sensor Circuit High Voltage
DTC P0222: Idle Speed Control (ISC) Motor Position Sensor Circuit Low Voltage
DTC P0223: Idle Speed Control (ISC) Motor Position Sensor Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
5-Volt Reference | P0122, P0222 | P0510, P2119 | P0122, P0222 | P0123, P0223 | --
Idle Motor Position Signal | P0222 | P2118 | P0222 | P0223 | --
Idle Motor Switch Signal | P0510 | -- | P0510 | -- | --
Throttle Position Sensor Signal | P0122 | P0510 | P0122 | P0123 | --
Idle Motor High Control | P2101, P2118 | P2101, P2118 | P2101, P2118 | P2101, P2118 | --
Idle Motor Low Control | P2101, P2118 | P2101, P2118 | P2101, P2118 | -- | --
Low Reference | -- | -- | P0123, P0223 | -- | --

### Typical Scan Tool Data

#### ISC Motor Position Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: ISC Motor Position Sensor 5%/3.66 Volts
5-Volt Reference | 0%/0.0 Volts | 0%/0.0 Volts | 0%/5.0 Volts
ISC Motor Position Signal | 0%/0.0 Volts | 0%/0.0 Volts | 0%/5.0 Volts
Low Reference | -- | 0 %/5.0 Volts | --

#### TP Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The engine is operating in Closed Loop. Parameter Normal Range: TP Position Sensor 5%/4.2 Volts
5-Volt Reference | 6%/0.4 Volts | 6%/0.0 Volts | 14%/5.0 Volts
Throttle Position Sensor Signal | 6%/0.0 Volts | 6%/0.0 Volts | 6%/5.0 Volts
Low Reference | -- | 6%/5.0 Volts | --

### Circuit/System Description

The throttle body assembly uses an idle speed control (ISC) system that contains a motor, throttle position (TP) sensor, motor position sensor, and an idle switch. The ISC system is used to control engine speed at idle. The engine control module (ECM) uses a high and low control circuit to control the ISC motor. A 5-volt reference and low reference supplied by the ECM is shared by both the TP and ISC motor position sensors. The TP and ISC motor position sensors each have a signal circuit to feedback voltage to the ECM. The ECM commands the ISC motor by pulse width modulating the voltage on the high and low control circuits to adjust the throttle angle for idle speed control. The motor position sensor is used by the ECM to monitor the position of the ISC motor for idle operation. The TP sensor is used by the ECM to monitor the position of the throttle blade. An idle switch is used by the ECM to monitor when the throttle blade is at it rest position to allow the ISC motor to control idle operation. With the throttle blade at the rest position, the idle switch will be closed. When the throttle blade is opened, the idle switch will be open.

The ISC system consist of the following circuits:

• | 5-volt reference

• | ISC motor high

• | ISC motor low

• | ISC motor position sensor signal

• | Idle switch signal

• | Low reference

• | TP sensor signal

### Conditions for Running the DTC

• | The ignition is ON or the engine is operating.

• | The DTCs runs continuously when the above condition is met.

### Conditions for Setting the DTC

#### P0122

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

#### P0123

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

#### P0222

The ECM detects that the ISC motor position sensor voltage is less than 0.257 volt.

#### P0223

The ECM detects that the ISC motor position sensor voltage is greater than 4.9 volts.

### Action Taken When the DTC Sets

• | DTC P0122 and P0123 are Type A DTCs.

• | DTC P0222 and P0223 are Type B DTCs.

### Conditions for Clearing the DTC

• | DTC P0122 and P0123 are Type A DTCs.

• | DTC P0222 and P0223 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### 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 scan tool TP Sensor or the ISC Motor Position Sensor parameters. The readings should be between 0.4-4.5 volts.
2. 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

1. Ignition OFF, disconnect the harness connector at the throttle body assembly.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 8 and ground.

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

Important: The 5-volt reference circuits are internally and externally connected at the ECM. Other component DTCs may be set. If other DTCs are set, review the electrical schematic and diagnose the applicable circuits and components.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground.

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

⇒ | If greater than the specified range, 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/ISC motor position sensor voltage parameter is less than 0.3 volt.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit terminal 2. Verify the scan tool TP sensor/ISC motor position sensor voltage parameter is greater than 4.8 volts.

• | TP Sensor signal circuit terminal 7

• | High Idle switch circuit terminal 4

⇒ | If less than the specified range, test the appropriate signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

6. If all circuits test normal, test or replace the throttle body assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Throttle Body Assembly Replacement

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