Circuit Description
The throttle body assembly contains a throttle position (TP) sensor. The TP sensor is mounted externally on the throttle body assembly. The TP sensor is a potentiometer which provides a signal voltage that changes relative to the throttle blade angle. The engine control module (ECM) supplies the TP sensor with a common 5-volt reference circuit, a common low reference circuit, and a signal circuit. The TP sensor signal voltage decreases from more than 4 volts at idle to less than 1 volt at wide open throttle (WOT).
If the ECM detects the TP sensor signal voltage is too high, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage
Conditions for Running the DTC
| • | The ignition is ON or the engine is operating. |
| • | DTC P0123 runs continuously once the conditions above are met. |
Conditions for Setting the DTC
The ECM detects that the TP sensor voltage is more than 4.9 volts.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records. |
| • | A history DTC is stored. |
| • | The TP angle will default to 0 percent when the vehicle speed is less than 3 km/h (2 mph) and 10 percent when the vehicle speed is greater than 3 km/h (2 mph). The scan tool will not display the default value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 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. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnecting the ECM battery feed for more than 10 seconds. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that a condition exists.
-
This step tests for a condition in the signal circuit of the TP sensor. If the TP sensor voltage parameter displays a voltage after the throttle body is disconnected, test for a short to voltage in the signal circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module 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 Intermittent Conditions |
Is the voltage less than the specified value? | 4.9 V | Go to Step 3 | Go to Step 4 | |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
Is the voltage less than the specified value? | 0.1 V | Go to Step 5 | Go to Step 8 | |
5 | Measure the voltage between the 5-volt reference circuit of the TP sensor and the ECM housing with a DMM. Is the voltage less than the specified value? | 5.2 V | Go to Step 6 | Go to Step 9 |
6 | Measure the voltage between low reference circuit of the TP sensor and the ECM housing. Is the voltage less than the specified value. | 1 V | Go to Step 7 | Go to Step 13 |
7 |
Is the resistance less than the specified value? | 10 ohms | Go to Step 11 | Go to Step 10 |
8 | Test the signal circuit of 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 16 | Go to Step 12 |
9 |
Important: The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors. Test the 5-volt reference circuit of the TP sensor and all shared 5-volt reference circuits 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 16 | Go to Step 12 |
10 | Test the low reference circuit of the TP sensor for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
11 | Test for shorted terminals and for poor connections at the throttle body assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
12 | Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 |
13 |
Important: The control module and/or the throttle body assembly may be damaged if the circuit is shorted to battery positive voltage. Repair the short to voltage in the low reference circuit of the TP sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
14 | Replace the TP sensor. Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
16 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 17 |
17 | Are there any DTCs that have not been diagnosed? | -- | System OK | |
