Circuit Description
The DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage diagnostic monitors the TP 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.
Conditions for Setting the DTC
| • | A high TP sensor voltage is indicated at the PCM. |
| • | The above condition is present for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM enters the Failsafe mode and assumes the engine throttle valve angle is 24.5 degrees (M/T) or 0 degrees (4 speed A/T). |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing cycles without a fault present. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
On a cold engine the TP sensor may indicate 3 percent or more with the throttle closed at idle. After the engine warms up and the plunger of the fast idle-up valve has retracted, the TP sensor will indicate 0 percent at idle.
If a DTC P0123 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool clear DTC information function. Road test the vehicle while monitoring the DTC P0123 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0123 appears in the Not Ran Since Code Cleared list, the DTC P0123 diagnostic has not yet run. When the DTC P0123 does not appear in the Not Ran Since Code Cleared list, the DTC P0123 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0123 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.
An intermittent malfunction may be caused by a fault in the TP sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0123 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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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.
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The percentage of TP sensor movement should not be more than 99 percent when observing the TP sensor parameter from closed throttle position to wide open throttle.
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This step determines whether the malfunction that caused the DTC P0123 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool clear DTC information function, the DTC P0123 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0123 appears in the Not Ran Since Code Cleared list, the DTC P0123 diagnostic has not yet run. When DTC P0123 does not appear in the Not Ran Since Code Cleared list, the P0123 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0123 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.
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The PCM supplies a small bias voltage of 5.0 volt on the TP sensor signal circuit. Because of this bias voltage the PCM sees 5 volts when the TP sensor signal circuit is open and sets a DTC P0123.
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A TP sensor that is out of specifications should be replaced.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0123 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0123 appears in the Not Ran Since Code Cleared list, the DTC P0123 diagnostic has not yet run. When the DTC P0123 does not appear in the Not Ran Since Code Cleared list, the DTC P0123 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0123 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||
Does the TP sensor percentage steadily increase within the specified range? | 0 - 99% | Go to Step 3 | Go to Step 4 | |||||
Did DTC P0123 set? | -- | Go to Step 4 | Go to Diagnostic Aids | |||||
4 |
Does the voltage equal the specified value? | 5 V | Go to Step 5 | Go to Step 8 | ||||
5 | Backprobe the TP sensor ground circuit at the TP sensor harness connector with a test lamp connected to B+. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10 | ||||
6 |
Is the TP sensor signal voltage within the specified range? | 0.35-0.65 V | Go to Step 12 | Go to Step 7 | ||||
Was a repair necessary? | -- | Go to Step 13 | Go to Step 9 | |||||
8 |
Was a repair necessary? | -- | Go to Step 13 | Go to Step 12 | ||||
9 |
Was a repair necessary? | -- | Go to Step 13 | Go to Step 11 | ||||
10 |
Was a repair necessary? | -- | Go to Step 13 | Go to Step 12 | ||||
Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | Go to Step 13 | -- | |||||
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 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 | |||||
