Circuit Description
The DTC P2121 Accelerator Pedal Position (APP) Sensor 1 Intermittent diagnostic detects an out of range APP sensor 1 signal. The accelerator pedal assembly contains 2 APP sensors. The APP sensors are mounted in the pedal assembly and are not serviceable. The APP sensors provide a signal voltage that changes relative to the position of the accelerator pedal. The powertrain control module (PCM) supplies a separate 5-volt reference and low reference circuit for each of the APP sensors.
The APP sensor 1 signal voltage increases as the pedal is depressed, from approximately 0.75 volts at rest to about 4 volts when fully depressed. The APP sensor 2 signal voltage increases as the pedal is depressed, from approximately 1.6 volts at rest to more than 4.8 volts with the accelerator pedal fully depressed.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2121 Accelerator Pedal Position (APP) Sensor 1 Intermittent
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P2121 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
The difference between APP sensor 1 voltage and APP sensor 2 voltage is less than 0.4 volts for less than 1 second.
OR
The difference between APP sensor 1 voltage and APP sensor 2 voltage is more than 1.2 volts for less than 1 second.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions that were present when the DTC set as Freeze Frame data. |
| • | The engine will operate in the reduced power mode and the APP sensor will default to idle. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip in which the diagnostic runs without a fault. |
| • | The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault. |
| • | You use the scan tool Clear DTC Information function. |
Diagnostic Aids
On a good APP sensor 1 the scan tool will typically display a voltage of 0.75-0.80 volts at idle. APP sensor 2 voltage will be 1.60-1.65 volts at idle.
An intermittent malfunction may be caused by fault in the APP sensor electrical circuits. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
Repair any electrical circuit faults that were found. Refer to Wiring Repairs .
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 on the diagnostic table.
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The Diagnostic System Check - Vehicle 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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This step determines if DTC P2121 is the result of a hard failure or an intermittent condition.
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This step inspects for an open or a short in the APP sensor 5-volt reference.
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This step inspects for excessive resistance in the reference voltage circuit. If the test lamp does not illuminate at all, there is resistance in the circuit.
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When the 5-volt reference circuit is jumpered to the APP sensor input circuit, the scan tool parameter should read 5 volts.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||||||
2 | Are there any other accelerator pedal position (APP) sensor DTCs set? | -- | Go to Step 3 | |||||
Does DTC P2121 set? | -- | Go to Step 4 | Go to Diagnostic Aids | |||||
Is the voltage of both APP sensors at the specified value? | 5 V | Go to Step 5 | Go to Step 8 | |||||
Does the test lamp illuminate at least dimly for both sensors? | -- | Go to Step 6 | Go to Step 8 | |||||
Are both APP sensor voltages at the specified value? | 5 V | Go to Step 9 | Go to Step 7 | |||||
7 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||
8 | Locate and repair the high resistance in the suspect reference voltage circuit of the APP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs . Did you complete the repair? | -- | Go to Step 11 | -- | ||||
9 | Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
10 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
11 |
Did DTC P2121 set? | -- | Go to Step 12 | Go to Step 2 | ||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
