Circuit Description
The throttle position (TP) sensor circuit provides a voltage signal that changes relative to the throttle blade angle. The signal voltage will vary from less than 1 volt at closed throttle, to approximately 4 volts at wide-open throttle (WOT). The TP signal is one of the most important inputs used by the PCM for fuel control, and for most of the PCM-controlled outputs. When the PCM detects an excessively high signal voltage on the throttle position sensor signal circuit, DTC P0123 will set
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
| • | The TP sensor signal voltage is more than 4.9 volts. |
| • | The above condition is present for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
A malfunctioning TP sensor -- With the ignition ON, and the engine OFF, observe the TP sensor display on a scan tool while slowly depressing the accelerator to wide-open throttle. If a voltage of more than 4.71 volts is seen at any point in the normal accelerator travel, replace the TP sensor.
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
The components that share the TP sensor 5-volt volt reference A circuit include the following devices:
-
When the PCM is replaced, you must program the new PCM.
| • | The EGR valve |
| • | The FTP sensor |
| • | The MAP sensor |
| • | Disconnect these components one at a time while you observe the TP sensor display on a scan tool. If the reading changes drastically when one of these components is disconnected, replace the component that affected the reading. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important: If DTC P1635 5 Volt Reference Circuit is set, perform that diagnostic first.
Is the voltage more than the specified value? | 4.7 V | ||
3 |
Does the DTC re-set? | -- | Go to Diagnostic Aids | |
4 |
Is the voltage at the specified value? | 0 V | ||
5 | Using a DMM, measure the voltage between the 5-volt reference circuit of the TP sensor and a known good ground. Is the voltage at the specified value? | 5.0 V | ||
6 | Connect a test lamp between the ground circuit of the TP sensor and the battery positive voltage. Does the test lamp illuminate? | -- | ||
7 |
Did you find and correct the condition? | -- | ||
8 | Test the signal circuit of the TP sensor for a short to voltage. Refer to Circuit Testing . Repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
Test all 5-volt reference A circuits and the connected components for a short to voltage. Refer to DTC P1635 5 Volt Reference Circuit . Repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | |||
10 | Inspect for faulty connections at the harness connector of the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections . Repair the condition as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
11 | Inspect for faulty connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections . Repair the condition as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
12 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | -- | |
|
Important: You must program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
14 |
Does the DTC reset? | -- | System OK |
