Circuit Description
The throttle position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from less than 1 volt at closed throttle to more than 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 most of the PCM controlled outputs. DTC P0123 will set when the PCM detects an excessively high signal voltage on the throttle position sensor signal circuit.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The TP sensor signal voltage is more than 4.9 volts. |
| • | The above conditions are present for more than 1 second. |
| . |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic runs and fails. |
| • | If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp. |
| • | 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
Check for the following conditions:
| • | A faulty connection at the PCM--Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper terminal tension. |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the TP sensor display on the scan tool while moving connectors and wiring harnesses related to the TP sensor. A change in the display will indicate the location of the malfunction. |
| • | A malfunctioning TP sensor--With the key ON and the engine not running, observe the TP sensor display on the scan tool while slowly depressing the accelerator to wide open throttle. If a voltage over 4.71 volts is measured at any point in normal accelerator travel, replace the TP sensor. |
If DTC P0123 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1121 diagnostic table may isolate the cause of the malfunction.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Components that share the TP sensor 5 volt reference A circuit include the following devices:
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This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
| • | The EGR valve |
| • | The engine oil pressure sensor |
| • | The manifold absolute pressure (MAP) sensor |
| • | Disconnect these components one at a time while observing the TP sensor display on the 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 | Was the Powertrain On Board Diagnostic (OBD) System Check performed? | -- | ||
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 scan tool indicate DTC P0123 failed? | -- | Go to Diagnostic Aids | |
4 |
Is the voltage equal to the specified value? | 0 V | ||
5 | Use a digital multimeter (DMM) in order to measure the voltage between the 5 volt reference circuit of the TP sensor and a known good ground. Does the voltage equal the specified value? | 5.0 V | ||
6 | Connect a test lamp between the ground circuit of the TP sensor and 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 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 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 and 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 and 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: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .Did you complete the replacement? | -- | -- | ||
14 |
Does the scan tool indicate DTC P0123 failed? | -- | System OK |
