Throttle Actuator Ctrl Sys-Idle Pos Not Learned
This code indicates that the PCM (or one of the other supporting control modules) has detected that the throttle actuator control system has failed to learn an acceptable idle position. These control modules may include (but are not limited to) the transmission control module, the body control module, the antilock brake control module, the instrument panel control module, the fuel injection control module, the turbo control module, the anti-theft module, the cruise control module, the traction control module, proximity alert module, and the climate control module.
Code Set Parameters
In the event that the throttle actuator control system has failed to learn an acceptable idle position, a trouble code will be stored and a service engine soon lamp will be illuminated. Some models require multiple drive cycles (as many as 8) with a failure in order for the service engine soon lamp to be illuminated and others will activate it on the initial failure.
Symptoms may include black smoke at startup, poor/no acceleration, a no start condition, misfire at idle, start and stall If this code is stored, and a service engine soon lamp has not yet been illuminated, the code may be shown as pending.
The most likely cause of this code being stored is caused by a programing error in one or more controllers. Carbon coking on the throttle plate and on the inner bore of the throttle body may also contribute to this code setting condition. The next most common malfunction is a defective manifold air pressure sensor. A defective throttle actuator control, throttle position actuator, throttle position sensor, or an engine vacuum leak could also be the cause of such a code. Other causes may include corroded, open, or shorted wiring or connectors in the CAN Bus harness, a loose control module ground strap or broken ground wire.
Throttle position actuators and sensors are frequently replaced in error when a simple cleaning of the inner throttle bore could have rectified the situation. Drive-by-wire throttle body components are typically not serviceable as individual parts and require replacement of the entire throttle body. Symptoms and stored codes that are present as a reaction to a communication failure are often misdiagnosed and repaired as the cause of the problem. Obviously, this leads to an unsuccessful repair. Engine misfire codes, lean exhaust codes, fuel injector codes, and virtually any other drivability or transmission code that is accompanied by a controller communication code can potentially be a pitfall for misdiagnosis. Follow the rule that says to diagnose codes in the order in which they are stored and you will improve you chances for a successful diagnosis. Utilize freeze frame data to help you determine which codes were stored first.
- Several tools will be instrumental in attempting to successfully diagnose this code
- A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in trying to perform a successful diagnosis
Begin with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
Crank the engine and inspect the vacuum hoses and throttle air inlet tube for vacuum leaks
- Repair or replace defective vacuum lines or components as required then clear the codes and retest the system to make sure the problem is repaired.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- Continue by clearing the code and operating the vehicle to see if it returns
- This will help to determine whether or not the malfunction is intermittent.
After the codes are cleared, test drive the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted
This type of code is only applicable to vehicles with an electronically controlled throttle body
- These types of systems are often referred to as “drive by wire” throttle bodies
- A sensor on the accelerator pedal arm inputs a voltage signal to the PCM (or other related controller) which commands the throttle body opened or closed, depending upon conditions
- Voltage signals from the PCM activate the throttle actuator motor in the direction required by changing voltage levels and polarity
- As the throttle actuator motor turns, it turns a gear in the throttle body that is meshed with a larger gear
- This change in ratio allows the throttle plate to be opened quickly and suddenly or slowly and gradually, depending upon the controller’s commands.
Remove the air intake hose from the throttle body and (with the ignition in the “OFF” position) open the throttle plate
- Inspect the inner bore of the throttle body for excessive amounts of carbon and clean the bore using a suitable solvent
- Clean the edge of the throttle plate, as well
- Clear the code and test drive the vehicle to ensure that your repair was successful
Test voltage and ground signals at the throttle actuator control motor connector, when the motor is activated using the scanner
- If voltage and ground signals are not present, disconnect the connector from the PCM and all related controllers and test individual circuits for resistance and continuity
- Repair or replace open, shorted, or disconnected circuits as required
- Clear the codes and test drive the vehicle to ensure a successful repair
If voltage and ground signals are present at the throttle actuator motor connector, when activated by the scanner, replace the motor, clear the codes, and drive the vehicle to ensure that your repair has been successful
- Most automakers do provide service parts for “drive by wire” throttle bodies
- It is likely that you will need to replace the entire throttle body, which typically includes the actuator motor and the throttle position sensor
- Pedal sensor replacement may also be recommended with throttle body replacement
- Consult the vehicle service manual (or equivalent) for the specific manufacturer’s recommendations
CAN is the abbreviation for “controller area network.” The CAN represents a communication bus that allows multiple microcontrollers to communicate with one another without the need for a host computer
- It is a message based protocol originally designed for automotive use
- The CAN bus network is actually a complex conglomeration of wiring harnesses and connectors used as a pipeline of information shared between two or more automotive control modules
- These controllers control virtually every electrical function of the vehicle, with the PCM being the primary controller
- Control modules receive input data from various sensors and emit output signals to system components and other control modules.
If this proves to be a CAN bus related condition, it could prove very difficult to diagnose by an amateur mechanic
- Unlike other diagnostic codes, this type of code can sometimes be best left to a professional simply because of the bulk of circuitry involved
- An experienced technician with a specialized scanner (Autohex or Tech II) may be able to determine the general area of the malfunction much more rapidly and easily than someone using a code reader and a digital volt ohmmeter
- Disconnecting and testing every single pin of the CAN bus could prove to be extremely time and cost prohibitive
- Additionally, some type of memory saving device must be installed, lest the PCM and other controllers lose their memory and require reprogramming
- A specialized diagnostic CAN scanner will show pin values and control module operation without risking a meltdown
- It can accurately diagnose computer and circuitry problems by monitoring vehicle operation while the vehicle is being operated
- To diagnose this type of code using a digital volt ohmmeter would entail probing thousands of circuits, independently
- One misplaced probe could destroy expensive control modules and require that the vehicle be totally reprogrammed.
At the most, you may attempt to perform a continuity test after all control modules are disconnected, and this could literally require 40-hours or more, depending upon the vehicle
- Some applications are equipped with up to 18 separate control modules.
If you choose to tackle this monumental task, begin with a careful visual inspection of all system circuitry, connectors, and fuses
- Control module ground circuits should be tested for continuity with battery ground
- These types of codes are frequently caused by defective or disconnected system grounds
- An auxiliary ground cable can be helpful in diagnosing system ground discrepancies
- Engine and transmission ground cables, straps, and wires are sometimes left dangling after repairs are performed
- Look for loose or corroded electrical connectors that may increase circuit resistance and cause these types of codes to be stored.
Obtain a CAN bus system wiring diagram and/or pin out value chart, then use the digital volt ohmmeter to test continuity between individual controller connectors
- Compare your findings with the manufacturer’s referenced values and repair open or shorted circuits as required
- It is often much more frugal to replace defective wiring rather than attempting to remove it from the complex web of wiring harnesses