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 below 1 volt at closed throttle to about 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 ignition is ON.
Conditions for Setting the DTC
| • | TP sensor signal voltage is greater than 4.9 volts. |
| • | Above conditions are present for longer than 1 second |
Action Taken When the DTC Sets
| • | The PCM will illuminate the MIL during the first 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been 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 the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. 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. |
| • | Malfunctioning TP sensor: With the key ON, 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 seen 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 Chart may isolate the cause of the malfunction.
Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table:
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Components that share the throttle position (TP) sensor 5 volt reference B circuit include the following devices:
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This vehicle is equipped with a powertrain control module (PCM) which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
| • | The exhaust gas recirculation (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 the components is disconnected, replace the component that affected the reading. |
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
2 |
Is the voltage more than the specified value? | 4.7 V | ||||||
3 |
Does the scan tool indicate DTC P0123 failed? | -- | Refer to Diagnostic Aids | |||||
4 |
Is the voltage near the specified value? | 0 V | ||||||
5 | Use a test lamp connected to B+ in order to probe the sensor ground circuit at the TP sensor harness connector. Does the test lamp illuminate? | -- | ||||||
6 |
Is the TP sensor signal circuit shorted? | -- | ||||||
Does disconnecting any of these components cause the TP Sensor display to change? | -- | |||||||
8 |
Is the circuit OK? | -- | ||||||
9 | Test for faulty electrical connections at the TP sensor and replace the terminals if necessary. Refer to Connector Repairs in Wiring Systems. Did you complete the repair? | -- | ||||||
10 |
Was a problem found? | -- | ||||||
11 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the repair? | -- | -- | |||||
|
Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the repair? | -- | -- | ||||||
13 |
Does the scan tool indicate DTC P0123 failed? | -- | System OK |
