Code Urgency and Drivability
The P2104 code indicates a serious issue with the throttle actuator control (TAC) system that is forcing the engine to remain at idle. When this code is triggered, the vehicle will have very limited or no throttle response and may fail to start. Driving the vehicle is not advisable as the engine is essentially locked in a "limp home" mode. It's best to have the vehicle towed to a dealer or repair shop for diagnosis.
In our workshop, we've encountered the P2104 code quite frequently across various car makes. Just last week, a customer brought in their 2012 BMW 328i with complaints of reduced engine performance and the check engine light on. Upon scanning, we found the P2104 code. After some troubleshooting, we traced the issue to a faulty accelerator pedal position sensor. Replacing the sensor resolved the problem. Similarly, we've seen this code pop up on several Volkswagen and Audi models, often due to wiring issues or a failing throttle actuator control motor. In my experience, while the P2104 code can affect any vehicle with electronic throttle control, it seems to be more prevalent on certain European makes like BMW, Mercedes, VW, and Audi compared to American or Asian brands.
Code Details
P2104 is a generic powertrain code that applies to vehicles with drive-by-wire electronic throttle control, including many models from Ford, GM, Toyota, Dodge, Chevy, Subaru, and others. The code definition is:
- P = Powertrain
- 2 = Manufacturer controlled
- 1 = Fuel and air metering
- 04 = Specific fault index
While the basic definition is universal, the exact failure thresholds and conditions that trigger a P2104 can vary between vehicle makes and models. Always refer to the manufacturer's service information for the specific vehicle when diagnosing this code.
Parts Involved
The main components related to a P2104 code are:
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- Throttle actuator control (TAC) motor – Controls the throttle plate position based on input from the accelerator pedal position sensor and PCM
- Accelerator pedal position (APP) sensor – Detects accelerator pedal movement and sends a signal to the PCM
- Powertrain control module (PCM) – Controls the TAC system and monitors for faults
Common Causes
A P2104 code can be triggered by several issues, including:
- Faulty electronic throttle body (ETB) or TAC motor
- Damaged APP sensor
- Wiring issues between APP sensor, TAC motor, and PCM
- Stuck or binding throttle plate
- PCM failure
In many cases, a P2104 will be accompanied by other related codes like P2110, P2105, or P2106.
Diagnosis Steps
- Scan for all codes and document freeze frame data.
- Visually inspect the ETB, wiring harness, and connectors. Look for corrosion, loose pins, or damaged wires.
- Check power and ground circuits to the ETB/TAC motor.
- Perform an ETB relearn procedure if applicable.
- Test the APP sensor and verify the correct voltage signal to the PCM.
- If no wiring or component faults are found, suspect a faulty PCM.
Repair Options
- Replace a faulty ETB/TAC motor assembly
- Repair damaged wiring or connectors
- Replace the APP sensor if it has failed
- Reflash or replace the PCM if it is faulty
Prevention and Cost
Proper maintenance like replacing the air filter and cleaning the throttle body can help prevent a P2104 code. However, most occurrences are caused by an electronic fault that cannot be prevented.
Repair costs will depend on the root cause:
- Throttle body cleaning: $75-150 / €65-130
- Throttle body replacement: $300-600 / €260-520
- APP sensor replacement: $100-300 / €85-260
- PCM replacement: $500-1500 / €430-1300
Related Codes
Other codes that may appear along with P2104 include:
- P2110 – TAC system forced limited power
- P2105 – TAC system forced engine shutdown
- P2106 – TAC system forced limited RPM
- P2135 – APP sensor circuit malfunction
- P0121 – APP sensor range/performance
By understanding the P2104 code definition, common causes, and diagnostic steps, technicians can efficiently troubleshoot and repair throttle actuator control system faults. Proper repair will restore normal throttle operation and allow the vehicle to be driven safely again.
Frequently Asked Questions About P2104
What does the P2104 code mean?
The P2104 code indicates that the throttle actuator control system has detected a malfunction and is limiting engine operation to an idle state as a failsafe measure. The engine control module (ECM) has forced the throttle to remain at idle regardless of accelerator pedal input.
What are the symptoms of a P2104 code?
Common symptoms of a vehicle with a P2104 code include:
- Engine stuck at idle speed and will not rev up
- Little to no throttle response
- Check engine light illuminated
- Reduced engine performance
- Vehicle may not start
Can I still drive with a P2104 code?
It is not advisable to continue driving a vehicle that has set a P2104 code. The throttle is essentially locked at idle which will make the vehicle very difficult to operate, especially at highway speeds. The underlying issue should be diagnosed and repaired as soon as possible.
What causes a P2104 code?
Potential causes of a P2104 code include:
- Faulty throttle body or throttle actuator motor
- Damaged accelerator pedal position sensor
- Wiring issues between accelerator pedal, throttle actuator, and ECM
- Stuck or binding throttle plate
- ECM failure
How do you diagnose a P2104 code?
To properly diagnose a P2104 code:
- Scan for all codes and document freeze frame data.
- Visually inspect throttle body, wiring, and connectors for damage.
- Check power and ground circuits to the throttle actuator motor.
- Perform a throttle body relearn procedure if applicable.
- Test accelerator pedal position sensor output.
- Check for ECM communication faults.
Can a bad throttle position sensor cause a P2104?
Yes, a faulty throttle position sensor that is not reading the throttle plate angle correctly can cause the ECM to set a P2104 code. The throttle position sensor is integral to the throttle actuator control system.
How much does it cost to fix a P2104 code?
The cost to repair a P2104 code will depend on the root cause:
- Throttle body cleaning: $75-150
- Throttle body replacement: $300-600
- Accelerator pedal sensor replacement: $100-300
- Wiring harness repair: $50-200
- ECM replacement: $500-1500
Can a vacuum leak cause a P2104 code?
No, a vacuum leak will not directly set a P2104 code as it deals with the electronic throttle control system. However, a large vacuum leak could cause idle issues that may result in related throttle control codes being set.
What does forced idle mean?
Forced idle refers to when the ECM commands the throttle plate to stay closed at the base idle position regardless of driver accelerator pedal input. This is a failsafe mode to prevent unintended acceleration if a throttle system fault is detected.
What is a throttle actuator?
The throttle actuator, also known as the throttle control motor, is the component that physically opens and closes the throttle plate. It receives a signal from the ECM that is based on accelerator pedal position.
Can low battery voltage cause a P2104?
Low battery voltage can potentially cause a P2104 if it drops below the normal operating threshold for the throttle actuator circuit. This could cause the throttle control motor to malfunction.
Can a bad accelerator pedal cause a P2104?
Yes, a faulty accelerator pedal position sensor can send an incorrect signal to the ECM which could set a P2104 code. The pedal sensor tells the ECM how far the driver is pressing the accelerator.
What does the throttle body do?
The throttle body contains the throttle plate which controls the amount of air entering the engine. This regulates engine speed and power output. The throttle plate is opened and closed by the throttle actuator motor.
What is limp mode?
Limp mode, also called failsafe mode, is when the ECM detects a major malfunction and limits vehicle performance to protect the engine. With a P2104 code, limp mode will keep the throttle closed so the engine remains at idle.
Can a clogged catalytic converter cause P2104?
No, a clogged catalytic converter will not directly cause a P2104 code. This code deals with the throttle control system on the intake side of the engine, while the catalytic converter is an exhaust component.
What does the accelerator pedal position sensor do?
The accelerator pedal position (APP) sensor monitors accelerator pedal movement and sends a corresponding voltage signal to the ECM. The ECM uses this signal to determine how much to open the throttle plate via the throttle actuator.
What other codes may be set along with P2104?
Related codes that may accompany P2104 include:
- P2135 APP sensor circuit malfunction
- P2138 APP sensor circuit low voltage
- P2101 throttle actuator circuit range/performance
- P2111 throttle actuator control system stuck open
- P2110 throttle actuator control system forced limited power
How do you do a throttle body relearn?
The throttle body relearn procedure varies by vehicle make and model. It typically involves:
- Scanning for codes
- Erasing codes
- Turning the ignition on and off
- Depressing the accelerator pedal
- Starting the engine and letting it idle
Consult the factory service manual for the exact procedure.
Can a bad mass airflow sensor cause a P2104 code?
A faulty mass airflow (MAF) sensor will not directly set a P2104 code, as the MAF is a separate component from the electronic throttle control system. However, significant inaccuracies in the MAF sensor reading could lead to drivability issues that may result in throttle control related codes being set.
What is the difference between P2104 and P2135?
While both codes deal with the electronic throttle control system, they indicate different issues:
- P2104 means the throttle is stuck at idle due to a system malfunction
- P2135 indicates a problem with the APP sensor signals being sent to the ECM
It is possible for both codes to be set simultaneously if the APP sensor is the component that has failed.