Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P2120: Accelerator Pedal Position (APP) Sensor 1 CircuitDTC P2121: Accelerator Pedal Position (APP) Sensor 1 Performance
DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage
DTC P2123: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage
DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit
DTC P2127: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage
DTC P2128: Accelerator Pedal Position (APP) Sensor 2 Circuit High Voltage
DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation
Diagnostic Fault Information
Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance |
|---|---|---|---|---|---|
APP Sensor 1 5-Volt Reference | P0606* | -- | P2120, P2122 | ** | -- |
APP Sensor 2 5-Volt Reference | P0606* | -- | P2125, P2127 | ** | -- |
APP Sensor 1 Signal | P2120, P2122 | P2121, P2138 | P2120, P2122 | P2120, P2123** | P2138 |
APP Sensor 2 Signal | P2125, P2127 | P2138 | P2125, P2127 | P2125, P2128** | P2138 |
APP Sensor 1 Low Reference | -- | P2138 | P2123, P2138 | -- | -- |
APP Sensor 2 Low Reference | -- | P2138 | P2128, P2138 | -- | -- |
*Engine cranks but won't start **Internal PCM or APP sensor damage may occur if the circuit is shorted to B+ | |||||
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: The ignition is ON and the engine is OFF. Parameter Normal Range: APP Sensor 1 0.75-0.80 volts | |||
5-Volt Reference | * | 0 volts | ** |
APP Sensor 1 Signal | 0 volts | 0 volts | 5.0 volts |
Low Reference | -- | 5.0 volts | -- |
*No scan tool communication with control module **Internal PCM or APP sensor damage may occur if the circuit is shorted to B+ | |||
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: The ignition is ON and the engine is OFF. Parameter Normal Range: APP Sensor 2 1.60-1.65 volts | |||
5-Volt Reference | * | 0 volts | ** |
APP Sensor 2 Signal | 0 volts | 0 volts | 5.0 volts |
Low Reference | -- | 5.0 volts | -- |
*No scan tool communication with control module **Internal PCM or APP sensor damage may occur if the circuit is shorted to B+ | |||
Circuit/System Description
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 greater than 4.8 volts with the accelerator pedal fully depressed.
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | The DTCs runs continuously when the above condition is met. |
Conditions for Setting the DTC
P2120
| • | The PCM detects that the APP sensor 1 voltage is less than 0.2 volts for less than 1 second. |
| OR |
| • | The PCM detects that the APP sensor 1 voltage is greater than 4.8 volts for less than 1 second. |
P2121
| • | The difference between the APP sensor 1 and the APP sensor 2 voltage is less than 0.4 volts for less than 1 second. |
| OR |
| • | The difference between the APP sensor 1 and the APP sensor 2 voltage is greater than 1.2 volts for less than 1 second. |
P2122
The PCM detects that the APP sensor 1 voltage is less than 0.2 volts for less than 1 second.
P2123
The PCM detects that the APP sensor 1 voltage is greater than 4.8 volts for less than 1 second.
P2125
| • | The PCM detects that the APP sensor 2 voltage is less than 0.5 volts for less than 1 second. |
| OR |
| • | The PCM detects that the APP sensor 2 voltage is greater than 4.8 volts for less than 1 second. |
P2127
The PCM detects that the APP sensor 2 voltage is less than 0.5 volts for less than 1 second.
P2128
The PCM detects that the APP sensor 2 voltage is greater than 4.8 volts for less than 1 second.
P2138
| • | The PCM detects that the difference between APP sensor 1 and APP sensor 2 is less than 0.2 volts for greater than 2 seconds. |
| • | The PCM detects that the APP sensor 1 voltage is less than 0.2 volts for greater than 2 seconds. |
| • | The PCM detects that the APP sensor 2 voltage is less than 0.5 volts for greater than 2 seconds. |
Action Taken When the DTC Sets
DTC P2120, P2121, P2122, P2123, P2125, P2127, P2128 and P2138 are Type A DTCs.
Conditions for Clearing the DTC
DTC P2120, P2121, P2122, P2123, P2125, P2127, P2128 and P2138 are Type A DTCs.
Diagnostic Aids
If a shared 5-volt reference circuit is shorted to ground the engine will not start and the PCM will not communicate with the scan tool.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Throttle Actuator Control (TAC) System Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe that the APP sensor 1 scan tool parameter is between 0.75-0.80 volts.
- Ignition ON, observe that the APP sensor 2 scan tool parameter is between 1.60-1.65 volts.
- Observe both APP sensor parameters while pressing the accelerator pedal from the rest position to the floor. Both APP sensor parameters should change.
- Rapidly depress the accelerator pedal from the rest position to the floor and release the pedal. Repeat the procedure several times. DTCs P2120, P2121, P2122, P2123, P2125, P2127, P2128 and P2138 should not set.
- Slowly depress the accelerator pedal to the floor and then slowly return the pedal to the rest position. Repeat the procedure several times. P2120, P2121, P2122, P2123, P2125, P2127, P2128 and P2138 should not set.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the accelerator pedal assembly.
- Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminals listed below and ground G104.
- Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminals listed below and ground.
- Verify both scan tool APP sensor parameters are 0 volts.
- Install a 3A fused jumper wire between the 5-volt reference circuit and the APP sensor signal circuit terminal as listed below. Verify the correct scan tool APP sensor parameter as indicated.
- If all circuits test normal, test or replace the accelerator pedal assembly.
| • | APP sensor 1 terminal 3 |
| • | APP sensor 2 terminal 1 |
| ⇒ | If greater than the specified range, test the low reference circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the PCM. |
| • | APP sensor 1 terminal 6 |
| • | APP sensor 2 terminal 4 |
| ⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the PCM. |
| ⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the PCM. |
| ⇒ | If greater than the specified range, test the appropriate signal circuit for a short to voltage. If the circuit tests normal, replace the PCM. |
Important: The following test must be performed on both APP sensor signal circuits.
| • | APP sensor 1 signal circuit terminal 5--5.0 volts |
| • | APP sensor 2 signal circuit terminal 2--5.0 volts |
| ⇒ | If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the PCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for control module replacement, setup, and programming |
