How to Solve Buick Porthole Trouble Code P2138 Completely

A Buick Porthole 2.0T made 2011 with 82 thousands kilometers,the owner described that vehicle can not accelerate well and there are some warning light on the instrument cluster.Here I will share this real repair case on how to solved Buick Porthole Trouble Code P2138 completely to reader,and hope this article can help you on your technician career.

 

What is the symptoms of P2138 trouble code?

Technician start car to test the symptoms of P2138,and find below:

1. Check engine light on

2. ESC light on

3. Engine power reduced

4. There is massage about “Check ESC” on the instrument cluster massage centre

 

What is P2138 trouble code?

Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation

 

Trouble Disagnose:

Read the trouble code by GDS2,it show P2138.Before repair this issue,we need to learn the konwledge of throttle actuator control system,the control system diagma show below.

The Engine Control Module (ECM) is the control center of the Throttle Actuator Control (TAC) system,ECM judge the purpose of driver according to the input signal of accelerator pedal position sensor,then calcuate the correspinding throttle response value according to the input of the throttle position sensor.The Engine Control Module(ECM) achieve throttle positioning by providing a pulse width modulation voltage to the throttle actuator motor.The engine control module swtich to engine power reduced mode when ECM detecting failure of throttle actuator control system.

 

The accelerator pedal assembly includes two accelerator pedal position(APP) sensor.The accelerator pedal position sensor is located on the accelerator pedal assembly and it is not repairable.The accelerator pedal position sensor provides a signal voltage that varies with the accelerator pedal position.The engine control module (ECM) provides independent 5V reference voltage and low level reference voltage to each accelerator pedal position sensor.

 

The opening angle of accelerator pedal position sensor 1 and 2 change from 0%~100%.When pressing the accelerator pedal,the voltage signal of the accelerator pedal position sensor 1 increases.If press accelerator from original position to full depress position,the voltage will change from 1.0V to 4.10V.When pressing the accelerator pedal,the voltage signal of  accelerator pedal position sensor 2 increases.Original rest position to full depressed positon,the voltage signal will change from 0.49V to 2.04V.The relationship between APP2 and APP2 is nearly 2 times

 

Opening angle:0%~100%

APP1:0.49~4.10

APP2:0.49~2.04

TPS1:4.29~0.80

TPS2:0.67~4.16

 

The control system diagma of throttle actuator show below

 

When does ECM generate P2138 trouble code?

1.The engine control module detects the voltage difference value between accelerator pedal sensor 1 and idling range over 0.25V when releasing the accelerator pedal.

2.The engine control module detects the voltage difference value between accelerator pedal sensor 2 and idling range over 0.31V when releasing the accelerator pedal.

3.The engine control module detects thevoltage difference value between accelerator pedal sensor 1 and 2 over 0.31V when pressing the accelerator pedal partially.

4.The engine control module detects thevoltage difference value between accelerator pedal sensor 1 and 2 over 1.70V when pressing the accelerator pedal fully.

5.The engine control module detects thevoltage difference value between accelerator pedal sensor 1 and 2 over 0.04 and voltage signal APP1 is more than 1.17.

6.The generation time of each of above contion is more than 1s or accumulate to 10s,the P2138 trouble code will generate.

 

Track the voltage curve of accelerator pedal position sensor 1 and 2 in the engine data stream by GDS2 diagnostic tool.(show in below pic).According to the voltage curve,we found voltage signal of APP1 and APP2 difference value are not expressed in multiple relation and the change of accelerator pedal position sensor 2 voltage signal is extremely unstable when failture occuring.

Use multi-meter to detect resistance value between accelerator pedal position sensor 2 to engine contral module,it displayed 0.4Ω,it is normal.This confuse me,what wrong ?

After analyzing,techincian believe that static wire resistance value is normal,but the temperature and shaking make great impact on wire line when vehicle engine running.The bad wire connection will be worse in the situation of changing of temperature and shaking.Technician try to use a jump wire to connect between APP2 and ECM(show below pic),the failure disappeared.So the failure is caused by this bad wire connection.

Failure Solution:Check the wire connection between accelerator pedal position sensor 2 and ECM,and make the wire connection firm.(wipe the conducting resin) After test,the failure disappeared.