Circuit Description
The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade angle.
The TP sensor signal voltage varies from about 0.5 volts at idle to about 4.5 volts at Wide Open Throttle (WOT). The TP sensor signal is one of the most important inputs used by the VCM for controlling the fuel 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 0 throttle angle. The measures the percent throttle from this point on. The DTC is a type A DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | Engine running |
| • | TP sensor voltage is less than 0.15 volts |
Action Taken When the DTC Sets
Important: The scan tool will not indicate a default value.
The VCM sets the DTC P0122. The VCM turns ON the MIL when DTC P0122 is reported, and 1 failure has occurred.
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 the 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 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 the throttle is closed, to over 4.5 volts (4500 mV) when the throttle is held at the Wide Open Throttle (WOT) position.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the TP signal measures less than 0.15 volt, then the fault exists.
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This test simulates the DTC P0123 (high voltage). If the VCM recognizes the high signal voltage, the VCM and the wiring are okay.
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This test simulates a high signal voltage in order to check for an open in the TP signal circuit.
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This step checks the 5 volt reference circuit for an open, short to ground, or a poor connection, or a faulty VCM.
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The VCM terminals GR12 and GR27 are spliced together inside the VCM. When checking the 5 volt reference for a short to ground, both the 5 volt reference circuits and all the components on the 5 volt reference circuits must also be checked.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 |
Important: Before clearing the DTCs use the scan tool to record the Freeze Frame and the Failure Records data. This data will be lost when the Clear Info function is used. Was the On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool display a throttle position signal less than the specified value? | 0.15 V | |||
Does the scan tool display a throttle position signal greater than the specified value? | 4.0 V | |||
Probe the TP sensor signal circuit with a test lamp connected to the B+. Does the scan tool display a throttle position signal over the specified value? | 4.0 V | |||
5 | The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables. | -- | Go to The Applicable DTC Table | |
Check for an open in the 5 volts reference circuit. Was a problem found? | -- | |||
Check the 5 volt reference for a short to the 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 the ground. Was a problem found | -- | ||
10 | Check for a faulty connection at the VCM. Was a problem found? | -- | ||
11 | Repair the circuit as necessary. Is the repair complete? | -- | -- | |
12 | Replace the faulty 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 . Is the replacement 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 |
