Circuit 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 that changes relative to throttle plate angle. The TP sensor signal voltage at idle is less than 0.5 volt. The TP sensor voltage is typically near 0 volt at idle, but could be as high as 0.5 volt. The TP sensor voltage should increase to above 4 volts at wide open throttle (WOT). If the ECM detects an excessively high signal voltage, DTC P0123 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 running. |
| • | DTC P0123 runs continuously once the above condition is met. |
Conditions for Setting the DTC
Important: The scan tool displays a voltage near 0.0 volts. Do not use the scan tool voltage parameter to determine if there is a TP sensor condition.
The ECM detects that the TP sensor signal voltage is more than 4.9 volts for a total of 2.5 seconds during a 5 second time period.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Test Description
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 | |||||||
2 |
Is the percentage more than the specified value? | 15% | Go to Step 4 | Go to Step 3 | ||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||
Is the percentage less than the specified value? | 15% | Go to Step 5 | Go to Step 7 | |||||||
5 | Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground. Does the voltage measure more than the specified value? | 5.2 V | Go to Step 9 | Go to Step 6 | ||||||
6 | Measure the resistance between the low reference circuit of the TP sensor and the engine control module (ECM) housing with a DMM. Is the resistance less than the specified value? | 2 ohms | Go to Step 10 | Go to Step 8 | ||||||
7 | Test the signal circuit of the 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 14 | Go to Step 11 | ||||||
8 |
Important: The ECM and TP sensor may be damaged if the circuit is shorted to battery positive voltage. Test the low reference circuit of the TP sensor for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
|
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 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 14 | Go to Step 11 | |||||||
10 | Test for an intermittent and for a poor connection at the TP sensor. 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 14 | Go to Step 12 | ||||||
11 | Test for an intermittent and for a poor connection 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 14 | Go to Step 13 | ||||||
12 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
13 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
