Circuit Description
The DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage diagnostic detects an out of range sensor signal. The TP sensor is a potentiometer whose resistance value changes along with the throttle valve position. The powertrain control module (PCM) provides a 5-volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and uses the voltage to calculate the percentage of throttle valve opening. The TP sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. The TP sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease.
Throttle Opening | TP Resistance | TP Percentage | TP Signal Voltage |
|---|---|---|---|
Large | High | High | High |
Small | Low | Low | Low |
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0123 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
The TP sensor input to the PCM is more than 4.9 volts for at least 5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions that were present when the DTC set as Freeze Frame data. |
| • | The TP sensor angle will default to 0 percent. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run, and the fault condition is no longer present. |
| • | A DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | On a good TP sensor the scan tool will typically display a TP angle of 8-10 percent at idle, and 76-77 percent at wide open throttle (WOT). |
| • | An intermittent malfunction may be caused by fault in the TP sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems. |
| • | The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Diagnostic System Check - Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step determines if DTC P0123 is the result of a hard failure or an intermittent condition.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | ||
With the throttle closed, select the TP sensor parameter on the scan tool. Is the TP sensor percentage within the specified value? | 7-11% | Go to Step 3 | Go to Step 4 | |
3 |
Does DTC P0123 set? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 | Is a DTC P0118 or P0453 also set? | -- | Go to Step 7 | Go to Step 5 |
5 |
Did the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 |
6 |
Did you find and repair a condition? | -- | Go to Step 13 | Go to Step 12 |
7 |
Did you find and correct a condition? | -- | Go to Step 13 | Go to Step 11 |
8 |
Did you find and correct a condition? | -- | Go to Step 13 | Go to Step 9 |
9 |
Did you find and correct a condition? | -- | Go to Step 13 | Go to Step 10 |
10 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
11 |
Did you find and repair a condition? | -- | Go to Step 13 | Go to Step 12 |
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
