Circuit Description
The engine control module (ECM) supplies a 5-volt reference voltage signal and a ground to the throttle position (TP) sensor. The TP sensor sends a voltage signal back to the ECM relative to the throttle plate opening. The voltage signal will vary from approximately 0.33 volts at closed throttle, to over 4.3 volts at wide open throttle (WOT).
The TP signal is used by the ECM for fuel control and for most of the ECM controlled outputs. The TP signal is one of the most important inputs used by the ECM for fuel control and most of the ECM controlled outputs.
Conditions for Setting the DTC
The TP sensor voltage indicates a throttle voltage greater than 4.9 volts.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The TP angle will default to 0 percent when the vehicle speed is less than 3 km/h (2 mph) and 10 percent when the vehicle speed is greater than 3 km/h (2 mph). The scan tool will not display the default value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
If the DTC P0123 cannot be duplicated, the information included in the Freeze Frame data can be useful. Use a scan tool information data to determine the status of the DTC. If the DTC occurs intermittently, using the diagnostic table may help isolate the problem.
With ignition ON and the throttle at closed position, the voltage should read between 0.2-0.9 volts and increase steadily to over 4.3 volts at WOT.
DTCs P0123 and P0113 stored at the same time could be result of an open sensor ground circuit.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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With the throttle closed, the TP sensor voltage should read less than 0.9 volts. If the TP sensor voltage does not read less than 0.9 volts inspect for a binding or sticking throttle cable.
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With the TP sensor disconnected, the TP sensor voltage should be less than 0.2 volts if the ECM and wiring are OK.
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Probing the ground circuit with a test light inspects the circuit for high resistance which will cause a DTC P0123 to set.
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A shorted 5-volt reference circuit will also set additional DTCs.
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The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | -- | Go to Step 2 | ||
Is the throttle position (TP) sensor voltage greater than the specified value? | 1 V | Go to Step 4 | Go to Step 3 | |
3 |
Is the TP sensor voltage greater than the specified value? | 3.9 V | Go to Step 4 | Go to Step 12 |
Is the TP sensor voltage less than the specified value? | 0.2 V | Go to Step 5 | Go to Step 6 | |
Probe the TP sensor ground circuit, terminal 3 at the TP sensor connector with a test light connected to B+. Does the test light illuminate? | -- | Go to Step 7 | Go to Step 9 | |
6 | Inspect the TP sensor signal circuit for an short to voltage and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
Inspect the 5-volt reference circuit for a short to B+ and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | |
8 | Inspect the TP sensor electric connector for a poor connection and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
9 | Inspect the TP sensor ground circuit for an open and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement Did you complete the repair? | -- | Go to Step 12 | -- |
Did you complete the repair? | -- | Go to Step 12 | -- | |
12 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 13 | Go to Step 2 |
13 | Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
