Circuit Description
The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade angle. The signal voltage varies from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT).
The VCM uses the TP signal, one of the most important inputs, for fuel control and for most of the VCM control outputs.
Each time the voltage drops below 1.25 volts and stops, the VCM assumes this value as the 0 throttle angle, and the VCM measures the percent throttle from this point on. The DTC P0123 is a type A DTC. The DTC P1122 is a type D DTC.
The Conditions for Setting the DTC
The DTC sets when the TP sensor is less than 0.25 volts (0.15 volts for 7.4L).
Action Taken When the DTC Sets
The VCM stores the DTC in History if the VCM detects an intermittent problem.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
The scan tool reads throttle position in volts. The TP should read about 0.45 to 0.85 volts with the throttle closed and the ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward Wide Open Throttle (WOT).
An open or short to ground in the 5 volt reference circuit or the TP sensor signal circuit results in a DTC P0122.
Refer to the Intermittent Conditions .
Scan the TP sensor signal while depressing the accelerator pedal with the engine stopped and the ignition ON. The display should vary from below 1.25 volts (1250 mV) when throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at the Wide Open Throttle (WOT) position.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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If the TP signal is less than 0.2 volt, then the fault is present.
-
This step simulates the DTC P0123: (high voltage) - If the VCM recognizes the high signal voltage, the VCM and the wiring are OK.
-
The VCM recognizes the voltage as over 4 volts, indicating that the TP sensor signal circuit and the VCM are OK.
-
This simulates a high signal voltage in order to check for an open in the TP sensor signal circuit.
-
This step checks the 5 volt reference circuit for an open, short to ground, or a poor connection or a faulty VCM.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the freeze frame and the failure records for reference because the Clear Info function will lose the data. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool display a throttle position signal less than the specified value? | 0.15V | |||
Does the scan tool display a throttle position signal greater then the specified value? | 4.0V | |||
Probe the TP sensor signal circuit with a test lamp connected to B+. Does the scan tool display throttle position signal over the specified value? | 4.0V | |||
The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | ||
Check for an open in the 5 volt reference circuit. Was a problem found? | -- | |||
7 | Check the 5 volt reference circuit for a short to ground. Was a problem found? | -- | ||
8 | Check the TP sensor signal circuit for an open. Was a problem found? | -- | ||
9 | Check the TP sensor signal circuit for a short to ground. Was a problem found? | -- | ||
10 | Check for a faulty connection at the VCM. Was a problem found? | -- | ||
11 | Repair the circuit as necessary. Refer to Wiring Repairs in Engine Electrical. Is the repair complete? | -- | -- | |
12 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the replacement complete? | -- | -- | |
13 | Replace the VCM. Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming (With KS Calibration PROM) . Is the action complete? | -- | -- | |
14 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
15 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
