P0638 B1 Throttle Actuator Range / Performance
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OBD-II Trouble Code - P0638 - Data Sheet
Throttle Actuator Control Range / Performance (Bank 1)
This Diagnostic Trouble Code (DTC) is a generic OBD-II transmission code. It is considered universal as it applies to all makes and models of cars (1996 and newer), although specific repair steps may differ depending on the model.
What does trouble code P0638 mean?
Some newer vehicles are equipped with drive-by-wire systems where the throttle body is controlled by a sensor on the accelerator pedal, the powertrain control module / engine control module (PCM / ECM), and an electric motor in the throttle body.
The PCM / ECM uses a Throttle Position Sensor (TPS) to monitor the actual throttle position, and when the actual position is out of range with the target position, the PCM / ECM sets DTC P0638. Bank 1 refers to the number one cylinder side of the engine, however most vehicles use one throttle body for all cylinders. This code is similar to P0639.
Most of this type of butterfly valve cannot be repaired and must be replaced. The throttle body is spring-actuated to keep it open in the event of engine failure, in some cases the throttle body will not respond at full failure and the vehicle will only be able to drive at low speed.
Note. If there are any DTCs related to the throttle position sensor, be sure to correct them before diagnosing the P0638 code.
Symptoms
Symptoms of a P0638 trouble code may include:
- Check Engine Light (Malfunction Indicator Lamp) is on
- Vehicle may shake when accelerating
Possible Causes of Code P0638
Reasons for this DTC may include:
- Pedal position sensor malfunction
- Throttle Position Sensor Malfunction
- Throttle Actuator Motor Malfunction
- Dirty throttle body
- Wire harness, loose or dirty connections
- PCM / ECM Malfunction
Diagnostic / repair steps
Pedal position sensor – The pedal position sensor is located on the accelerator pedal. Typically, three wires are used to determine pedal position: a 5V reference signal supplied by the PCM/ECM, ground, and a sensor signal. A factory wiring diagram will be required to determine which wire is being used. Make sure the connection is secure and there are no loose wires in the harness. Use a digital volt-ohmmeter (DVOM) set to ohm scale to test for good grounding by connecting one wire to ground at the sensor connector and the other to chassis ground - the resistance should be very low. Test the 5 volt reference from the PCM using the DVOM set to volts with the positive wire at the harness connector and the negative wire at a known good ground with the key in the run or on position.
Check the reference voltage with the DVOM set to volts, with the red wire at the reference and the negative wire at a well known ground with the key in the run/on position - signal voltage should increase the further you press the gas pedal. Typically, the voltage ranges from 0.5 V when the pedal is not depressed to 4.5 V when the throttle is fully open. It may be necessary to check the signal voltage at the PCM to determine if there is a voltage difference between the sensor and what the PCM is reading. The encoder signal should also be checked with a graphical multimeter or oscilloscope to determine if the voltage increases smoothly without dropouts over the entire range of motion. If an advanced scan tool is available, the position sensor is usually displayed as a percentage of the desired throttle input, verify that the desired value is similar to the actual pedal position.
Throttle position sensor – The throttle position sensor monitors the actual position of the throttle body vane. The throttle position sensor is located on the throttle body. Typically, three wires are used to determine pedal position: a 5V reference signal supplied by the PCM/ECM, ground, and a sensor signal. A factory wiring diagram will be required to determine which wire is being used. Make sure the connection is secure and there are no loose wires in the harness. Use a digital volt-ohmmeter (DVOM) set to ohm scale to test for good grounding by connecting one wire to ground at the sensor connector and the other to chassis ground - the resistance should be very low. Test the 5 volt reference from the PCM using the DVOM set to volts with the positive wire at the harness connector and the negative wire at a known good ground with the key in the run or on position.
Check the reference voltage with the DVOM set to volts, with the red wire at the reference and the negative wire at a well known ground with the key in the run/on position - signal voltage should increase the further you press the gas pedal. Typically, the voltage ranges from 0.5 V when the pedal is not depressed to 4.5 V when the throttle is fully open. It may be necessary to check the signal voltage at the PCM to determine if there is a voltage difference between the sensor and what the PCM is reading. The throttle position sensor signal should also be checked with a graphical multimeter or oscilloscope to determine if the voltage increases smoothly without dropping out over the entire range of travel. If an advanced scan tool is available, the position sensor is usually displayed as a percentage of the actual throttle position, verify that the desired position value is similar to the position setpoint.
Throttle actuator motor – The PCM/ECM will send a signal to the throttle actuator motor based on the input pedal position and a predetermined output value depending on the operating conditions. The pedal position is known as desired input because the PCM/ECM controls throttle position and can limit its performance under certain conditions. Most drive motors have a duty cycle. Test the throttle motor for proper resistance by disconnecting the harness connector with a DVOM mounted on the ohm scale with positive and negative leads at both ends of the motor terminals. The resistance must be within the factory specifications, if it is too high or too low, the motor may not move to the desired position.
Check the wiring by checking for power using the factory wiring diagram to find the right wires. The power wire can be tested with the DVOM set to volts, with the positive wire on the power wire and the negative wire on a known good ground. The voltage should be close to the battery voltage with the key on in the run or on position, if there is a significant power loss the wiring may be suspicious and should be traced to determine where the voltage drop is occurring. The signal wire is grounded through the PCM and is turned on and off by a transistor. Duty cycle can be checked with a graphical multimeter or an oscilloscope set to the duty cycle function with the positive lead connected to the signal wire and the negative lead to a well known ground - a standard voltmeter will only display medium voltage which can be harder to determine if there is any voltage drops over time. The duty cycle must match the percentage set by the PCM/ECM. It may be necessary to check the specified duty cycle from the PCM/ECM with an advanced scan tool.
Throttle body – Remove the throttle body and check for any obstructions or accumulations of dirt or grease around the throttle that could interfere with normal movement. A dirty throttle can cause the throttle to not respond properly when commanded to a certain position by the PCM/ECM.
PCM / ECM - After checking all other functions on the sensors and the engine, the PCM/ECM can be tested for the desired input, actual throttle position, and engine target position using an advanced scan tool that will display the input and output as a percentage. If the values do not match the actual numbers received from the sensors and the motor, there may be excessive resistance in the wiring. The wiring can be checked by disconnecting the sensor harness and the PCM/ECM harness using the DVOM set to the ohm scale with the positive and negative wire at both ends of the harness.
You will need to use the factory wiring diagram to find the correct wires for each component. If the wiring has excessive resistance, the numbers displayed by the PCM / ECM may not match the desired input, target output, and actual output, and a DTC will set.
P0638 BRAND SPECIFIC INFORMATION
- P0638 HYUNDAI Throttle Actuator Range/Performance
- P0638 KIA Throttle Actuator/Range Control
- P0638 MAZDA Throttle Range/Performance
- P0638 MINI Throttle Actuator Control Range/Performance
- P0638 MITSUBISHI Throttle Actuator Range/Performance
- P0638 SUBARU throttle actuator adjustment range
- P0638 SUZUKI Throttle Actuator Control Range/Performance
- P0638 VOLKSWAGEN Throttle Range/Performance
- P0638 VOLVO Throttle Control Range Range/Performance
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