Fault code P0638 – throttle actuator control range/performance (Bank 1)

Fault code P0638 is called “Throttle Actuator Control Range/Performance (Bank 1)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0638

Some newer vehicles are equipped with an electronically actuated throttle body, in which the throttle is controlled by a sensor on the accelerator pedal. The powertrain control module (PCM) receives the signal from the sensor and transmits the command to the electric motor in the throttle body.

Fault code P0638 – throttle actuator control range/performance (Bank 1)

Also, the PCM uses the throttle position sensor (TPS) to monitor the actual throttle position. When the actual position is out of range with the target position, the PCM sets code P0638 for Bank 1.

Most throttle valves of this type are beyond repair and require replacement.

The throttle valve is actuated by a spring to hold it open in the event of an engine failure. In some cases of complete failure, the throttle will not respond and the vehicle will only be able to move at low speed.

OBD-II error P0638 is a generic code that is defined as “Throttle actuator control operating range mismatch (Bank 1)”. It is set when the Powertrain Control Module (PCM) detects a problem with the operation of the throttle control actuator.

When this trouble occurs, the throttle actuator does not operate as expected under a particular set of operating conditions. Or the actual throttle position does not match the desired position under the specified set of operating conditions.

Symptoms of vehicle malfunctions

The main signal that an error P0638 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine light on the control panel will illuminate (the code will be stored as a fault).
  2. Ignition jerking/missing at idle or under load.
  3. The engine stops or starts badly.
  4. Engine cannot be accelerated, throttle response is unresponsive.
  5. Bad acceleration.
  6. Loss of engine power due to slow throttle response.

Error P0638 is considered serious, as it can cause engine and handling problems. If this code is found, it is recommended that you take action to correct the error as soon as possible.

Factors that can cause this error code

The error code P0638 can mean that one or more of the following problems have occurred:

  • Faulty throttle position sensor.
  • Faulty accelerator pedal position sensor.
  • Throttle control motor malfunction.
  • Throttle control circuit failure or bad electrical connection of TPS, PPS and PCM sensors.
  • TPS, PPS sensor wiring harness is shorted.
  • Contamination of throttle body.
  • Throttle choke return spring is jammed.
  • Throttle choke clogging.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0638

Some suggested steps for troubleshooting and fix the error code P0638:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances the error P0638 appeared.
  2. Clear the error codes from the computer memory and test drive the vehicle to find out if the fault reappears.
  3. Visually inspect the electrical wiring and connections relating to the throttle position or accelerator pedal position sensor for looseness and damage.
  4. Test the TPS, PPS sensor.
  5. Check the return spring for proper operation.
  6. Clear error code from computer memory again, test drive vehicle to see if problem is resolved.

Diagnose and repair of problems

If the sensors have been recently replaced, it may be necessary to adjust the TPS, PPS. On some vehicles, the installation instructions require a proper adjustment to prevent the P0638 error from occurring.

If there are no symptoms, the problem may be intermittent, and clearing the code can sometimes temporarily resolve it. In this case, you should definitely check the wiring to make sure it’s not chafing or frayed anywhere, etc.

Accelerator pedal position and throttle position sensor

There are usually three wires on these sensors: a 5V reference voltage supplied by the PCM computer, ground, and a sensor signal. Make sure all connections are secure and there are no loose wires in the harness.

Check grounding reliability with a digital voltmeter set to ohm scale. Also test the reference voltage from the PCM, it should be 5 volts. The position sensor signal should also be tested with a multimeter to determine if the voltage increases smoothly without drooping over the entire range of motion.

The oscillation range should be from 0.5V to 4.5V. The minimum value is displayed when the pedal is not depressed. The maximum when the pedal is fully depressed, when the throttle is in the fully open position.

Throttle actuator motor

The PCM sends a signal to the throttle actuator motor depending on the pedal input position. And also a predetermined output value depending on operating conditions.

Check the throttle motor for proper resistance by disconnecting the wiring harness connector. The resistance should be within factory specifications, if it is too high or too low, the motor may not move to the specified position.

Check the wiring harness for power with a multimeter set to the volt scale. The voltage should be close to the battery voltage when the key is in the on position.

The duty cycle of the signal wire can be checked with a graphing multimeter or oscilloscope set to the duty cycle function. The duty cycle should match the percentage set by the PCM.

It may be necessary to check the set duty cycle from the PCM using an advanced diagnostic tool.

Throttle body

The P0638 error may also appear due to throttle body contamination when something is obstructing the free flow. Therefore, remove the throttle body and check for accumulations of dirt or fouling that could interfere with normal movement.

A dirty throttle body may not respond correctly when receiving a command from the PCM for a certain opening position.

On which vehicles does this problem occur most frequently

Fault code P0638 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (A4, Q5, Q7)
  • Chevrolet (Captiva)
  • Citroen
  • Fiat (Albea, Doblo, Ducato)
  • Hyundai (Elantra, Grandeur, Solaris, Tucson, Veloster, i40, ix35)
  • Isuzu (D-Max)
  • Kia (Ceed, Cerato, Rio, Sportage)
  • Mazda (3, 6)
  • Mercedes-Benz (Sprinter)
  • Mini (Cooper)
  • Mitsubishi (L200, Lancer, Pajero)
  • Nissan (Almera, Terrano)
  • Opel (Antara)
  • Peugeot (Boxer)
  • Porsche (Cayenne)
  • Renault (Duster, Fluence, Logan, Megane, Scenic)
  • Saab (9-3)
  • Skoda (Octavia)
  • Subaru (Forester, Impreza, Legacy, Outback, Tribeca)
  • Suzuki (Grand Vitara)
  • Volkswagen (Golf, Jetta, Passat, Polo, Touareg)
  • Volvo (S80)

Fault code P0638 can sometimes be found with other errors. The most common are the following: P0121, P0130, P0220, P0221, P0403, P0606, P0639, P0642, P0685, P1295, P1690, P2106, P2112.

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