Schematic Reference: Engine Controls Schematics
Circuit Description
The Throttle Position (TP) Sensor is a potentiometer whose resistance value changes along with the throttle valve position. The powertrain control module (PCM) provides a 5 volt reference voltage to the TP sensor. The PCM reads the voltage across the TP Sensor and uses the voltage to calculate the percentage of throttle valve opening. The TP sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. The TP Sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease.
Conditions for Running the DTC
| • | Engine speed is increasing. |
| • | Engine is operating in Closed Loop. |
Conditions for Setting the DTC
Vehicle speed has exceeded 30 km/h (19 MPH), and the output value of the throttle position sensor is out of the applicable range.
Action Taken When the DTC Sets
| • | The PCM illuminates the MIL during the second key cycle in which the DTC sets. |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame Data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Inspect the throttle valve linkage and lever assembly for free and normal movement. Binding or misalignment of the throttle valve can affect TP sensor input. Check that the throttle lever has not been bent or tampered with. Check that the throttle valve opens fully and the lever contacts the throttle stop.
The scan tool will typically display a TP Angle of 8-10% at idle, and 76-77% at wide open throttle (WOT).
An intermittent malfunction may be caused by fault in the TP sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connectors locks. |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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The throttle angle percentage should steadily increase without binding or a large percentage jump.
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This step determines if DTC P0121 is the result of a hard failure or an intermittent condition.
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This check whether there is a short to voltage or the TP sensor is binding.
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When the 5 volt reference circuit is jumpered to the TP sensor input circuit, the scan tool parameter should read near 100%.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
Does the TP angle value increase steadily when the accelerator pedal is depressed and decrease steadily when the pedal is released within the specified range? | 10-80% | |||||||||
Does the DTC P0121 set? | -- | Go to Diagnostic Aids | ||||||||
Is the TP sensor percentage greater than the specified value? | 0% | |||||||||
Is the TP sensor percentage greater than the specified value? | 90% | |||||||||
6 |
Was a problem found? | -- | ||||||||
7 |
Was a repair necessary? | -- | ||||||||
8 | Inspect and adjust the TP sensor as necessary. Refer to Throttle Position Sensor Adjustment . Did the TP sensor require adjustment? | -- | ||||||||
9 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | ||||||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |||||||
11 |
Are any DTCs displayed on scan tool? | -- | Go to the applicable DTC table | System OK |
