WHERE IS THE app SENSOR AND HOW TO CHANGE - 2003 Dodge Ram Pickup 1500

DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

P2138
• The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 0.23 volt, 0.25 volt for LLT, with the pedal released.
• The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 0.29 volt, 0.31 volt for LLT, with a partially pressed pedal.
• The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 1.66 volts, 1.70 volts for LLT, with a fully pressed pedal.
• Any of the above conditions exist, then a 5 second delay for MIL ON.

Diagnostic Aids
Test the current output of the 5-volt reference circuits if you suspect high resistance in the circuit. The current output should be greater than 80 mA for APP 1 and greater than 50 mA for APP 2.


If you don't know how to test the 5 volt reference circuits you need to take it to a qualified repair shop.


Circuit/System Verification
Ignition ON, observe the DTC information with a scan tool. DTC P0651, P0652, P0653, P0697, P0698, or P0699 should not be set.
? If a DTC is set, refer to DTC P0641-P0643, P0651-P0653, or P0697-P0699.
Observe the scan tool APP Sensor voltage parameters. Verify both of the APP sensor voltages are between 0.74-4.82 V.
Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release pedal. Repeat the procedure several times. DTCs P2122, P2123, P2127, P2128, or P2138 should not set.
Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times. DTCs P2122, P2123, P2127, P2128, or 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, remove the fuse that supplies B+ to terminal 56-X2 of the ECM.
Disconnect the harness connector at the accelerator pedal assembly.
Test for less than 5 ? between the appropriate low reference circuit of the APP sensor and ground.
? If greater than the specified range, test the low reference circuit of the APP sensor for a short to voltage, or an open/high resistance. If the circuit/connections test normal, replace the ECM.
Install the fuse that supplies B+ to terminal 56-X2 of the ECM.
Note: The 5-volt reference circuit voltage can be within the specified range with a high resistance in the circuit. If this condition is suspected, refer to Diagnostic Aids.
Ignition ON, test for 4.8-5.2 V between the appropriate 5-volt reference circuit of the APP sensor and ground.
? If less than the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.
? If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
Observe the appropriate scan tool APP sensor voltage parameter. Verify the voltage is less than 0.3 volt.
? If greater than the specified range, test the signal circuit of the applicable APP sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.
Connect a 3 A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit of the APP sensor. Verify the APP sensor voltage parameter is greater than 4.8 V.
? If less than the specified range, test the appropriate signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
? If both APP sensor voltage parameters display greater than 4.8 V test the signal circuits of the APP sensors for a shorted together condition. If the circuit/connections test normal, replace the ECM.
If all circuits/connections test normal, test or replace the accelerator pedal assembly.

These codes appear to relate to your throttle poistion sensor(s) - check your throttle cable linkages and in particular the position sensor on the throttle body.

code p 0125 refers to insufficient coolant temperature for closed loop fuel control===causes ---wiring --- cooling system---coolant thermostat---ECT sensor---ECM
code p1285 for isuzu refer to accelerator pedal position sensor 3 circuit
the accelerator pedal position (APP) sensors are located within the throttle actuator control (TAC) module assembly
The TAC module assembly is mounted to the accelerator pedal bracket
There are 3 individual APP sensors within the TAC module
3 separate signal circuits, low reference circuits , and 5 -volt references circuits are used in order to determine the APP
The APP signal voltage increases when the accelerator pedal is depressed

.The control module provides the APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensor then provides the control module a signal voltage proportional to pedal movement. The APP sensor 2 signal voltage is low at rest and increases as the pedal is depressed. When the control module detects that the APP sensor 2 signal or the APP sensor 5-volt reference voltage is outside the predetermined range, DTC P2125 sets.

The control module provides the APP sensors a 5-volt reference circuit and a low reference circuit. The APP sensors then provide the control module signal voltages proportional to pedal movement. The APP sensor 1 signal voltage is low at rest and increases as the pedal is depressed. The APP sensor 2 signal voltage is also low at rest and increases as the pedal is depressed. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. Two APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. However, if two or more DTCs are set involving more than one APP sensor, DTC P1125 will set.

code p 2138 refers to throttle position (TP) sensor/switch D/E-- voltage correlation=== causes --- wiring -- tp sensor /switch

code p 2122 refers to accelerator pedal (APP) sensor /switch D --low input===causes --wiring short to ground --APP sensor/ switch

also refers to engine control module (ECM) , idle control ---high input===causes ---wiring short to positive --TP sensor--ETS control valve (ETS----electronic throttle system)

Reduced Engine Power Mode When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
?€¢
Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.

?€¢
Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.

?€¢
Throttle default mode--The ECM will turn OFF the throttle actuator motor and the throttle will return to the spring loaded default position.

?€¢
Forced idle mode--The ECM will perform the following actions:

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Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF

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Ignore the accelerator pedal input

?€¢
Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.
Did you have it checked for DTC's - diagnostic trouble code's related to the reduced engine power ?
All so has APP sensor gas pedal !
Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
?€¢
A 5-volt reference circuit

?€¢
A low reference circuit

?€¢
A signal circuit

The APP sensors are used to determine the pedal angle. The engine control module (ECM) provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at rest position is less than 1 volt and increases to more than 4 volts as the pedal is actuated. The APP sensor 2 signal voltage at rest position is less than 0.6 volt and increases to more than 2 volts as the pedal is actuated.
Your best bet is take your vehicle to the dealer !
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Were the APP codes there BEFORE they replaced the BCM? APP codes usually are an indicator the throttle body needs to be replaced. As a precaution, some recommend to replace the throttle body AND the sensor on the gas pedal together. Unfortunately, this is a dealer only repair most o the time, since the ECM will have to be flashed to sync the new sensors.

First of all a scan tool is need for this not a code reader, you need to view scan data after you find what code is stored in the PCM. It could have a problem with the powertrain control module, wiring, or the Accelerator Pedal Position (APP) Sensors. Here are a few codes that could set .
DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit

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

Your vehicle has electronic throttle control . Position sensor's in the gas pedal an the throttle body , inputs to the Throttle Actuator Control Module
The TAC module is the control center for the throttle actuator control system. The TAC system is self-diagnosing and provides diagnostic information to the PCM through a dedicated serial data line. The TAC achieves throttle positioning by providing a pulse width modulated voltage to the TAC as directed by the PCM.

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system components include the following:
• The accelerator pedal position (APP) sensors
• The throttle body assembly
• The throttle actuator control module
• The powertrain control module (PCM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal assembly contains 2 individual APP sensors within the assembly. The accelerator pedal position (APP) sensors 1 and 2 potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The APP sensors are used to determine the pedal angle. The control module provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors then provide the control module with signal voltage proportional to pedal movement. APP sensor 1 signal voltage is low at the rest position and increases as the accelerator pedal is applied. APP sensor 2 signal voltage is high at the rest position and decreases as the accelerator is applied.
Throttle Body Assembly
The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle actuator motor. The throttle body functions similar to a similar to a conventional throttle body with the following exceptions:
• An electric motor opens and closes the throttle valve.
• The throttle blade is spring loaded in both directions and the default position is slightly open.
• There are 2 individual TP sensors within the throttle body assembly.
The TP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

Flickering light's could be caused by a bad diode in the alternator . Fluctuating idle could be caused same alternator problem or dirty throttle plate.
Throttle Body Cleaning To Restore Idle Quality

Throttle/Pedal Position Sensor/Switch "D" Circuit Low
P2122 - APP Sensor 1 Low Input

Probable Causes:
1 - Failed APP Sensor 1
2 - Open or short circuit condition
3 - Poor electrical connection

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P2138 - APP Sensor Performance Condition Fault

Probable Causes:
1 - Failed APP Sensor
2 - Open or short circuit condition
3 - Poor electrical connection
I hope this helps you and thank you