The OBD2 code P2104 is related to the Throttle Actuator Control (TAC) System, where the engine’s control unit (ECU) forces the throttle to idle. This code indicates that the ECU has detected an issue within the throttle actuator or related components, leading to an automatic default mode to prevent engine damage or unsafe conditions.
P2104 quick overview
| Meaning | P2104: Throttle Actuator Control (TAC) System – Forced Idle |
| Is it serious? | Yes, it can lead to drivability issues, including stalling or limited engine power. |
| Possible causes | – Faulty throttle body – Wiring or connection issues in the TAC system – PCM issues (software or hardware) |
| How to diagnose? | Inspect the throttle pedal assembly for issues. Test circuits within the TAC system for faults. Verify continuity and condition of the wiring harness. Consider replacing the throttle body assembly if the wiring and connections are intact. |
P2104 Meaning
For those not familiar with car mechanics, the P2104 code means there’s a problem with the part of your engine that controls how much air mixes with the fuel. This part is called the throttle, and it can be thought of as the “air gate” for your engine. When something goes wrong here, your car’s computer decides to play it safe by not letting the engine rev up, which is why it might just idle or not respond when you press the gas pedal. The issues can range from simple wiring problems to needing a new part for the throttle.
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How to fix P2104 – learn from mechanics
I looked into P2104 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Ford
Vehicle information 2005 Ford E-450 Super Duty 6.8L
Issue + repair history
- Vehicle experiencing severe running issues.
- Previous repair attempt:
- Cleaned connections on the throttle actuator control (TAC) system.
- Cleared trouble codes, temporary resolution.
- Mention of potential need for throttle housing replacement due to observed slop in throttle plate shaft.
Other OBD2 Codes + Test Results
- P2104: Throttle actuator control system forced idle.
- P2112: Actuator system stuck closed.
- P2111: Actuator system stuck open.
Mechanic suggestions
- Inspect throttle pedal assembly for potential issues.
- Test circuits in TAC system.
- Verify continuity through wiring harness.
- Consider replacing throttle body assembly if wiring is intact.
- Suggest consulting repair databases like AllData for detailed information.
Final fix
- Temporary fix: cleaned connections on TAC system.
- Potential future repair: throttle housing replacement if problem recurs due to observed slop in throttle plate shaft.
Case #2: Mercury
Vehicle information 2008 Mercury Grand Marquis GS 4.6L
Issue + repair history
- Taxi involved in a left front tire blowout, damaging the main harness.
- Another shop attempted repairs unsuccessfully.
- Main harness repaired, including data lines.
- Vehicle does not communicate or crank with throttle body motor connector plugged in.
- Throttle plate chatters at 28% duty, does not open when keyed up.
- Codes:
- P2100: TAC motor circuit open.
- P2104: TAC system forced idle.
- P2107: TAC module processor.
- P2110: TAC system forced limited idle.
- Previous repair attempts:
- Repaired wiring harness.
- Replaced PCM.
- Replaced throttle body.
Other OBD2 Codes + Test Results
- Hsc-h: 2.53v
- Hsc-l: 2.41v
Mechanic suggestions
- Pinout wires from ECM to throttle body, check resistance, ensure correct location.
- Ensure proper repair of data lines, recommend replacing harness if necessary.
- Check for cross-spliced wires, particularly if similar color wires are involved.
- Consider replacing harness due to sensitivity of CAN systems and potential for variance in resistance.
- Investigate possibility of etched or re-written processor in PCM due to harness destruction.
- Perform full vehicle scan to assess module communication.
Final fix
- Identified partially damaged wire powering PCM at connector C175b terminals 35 and 36, affecting throttle operation and PCM shutdown.
Case #3: Ford
Vehicle information 2005 Ford Escape Hybrid 2.3L
Issue + repair history
- Vehicle initially came in with heavy engine knock, requiring engine replacement.
- Engine swap performed, including transfer of all parts from old engine to new engine block.
- After swap, engine did not idle and dashboard showed multiple warning lights.
- Codes replaced except for P2104.
- No information available for most codes through AllData.
- Harness checked for any issues, technician found no problems.
Other OBD2 Codes + Test Results
- P0606: PCM Processor Fault.
- P1A10: Hybrid Powertrain control module – battery disabled.
- P1A13: Hybrid Powertrain Control Module Regenerative Braking Disabled.
- P2104: TAC System forced idle.
Mechanic suggestions
- Suggests a possible reflash for PCM to recognize and communicate with all systems.
- Speculates potential PCM damage due to electrical issues during engine swap.
- Raises concern about compatibility of the replacement engine, specifically whether it is a 2.3L Atkinson Hybrid engine.
- Contact information provided for further discussion, especially regarding hybrid powertrain controls.
Final fix
- Low hybrid battery state of charge caused hybrid-related codes.
- No start issue due to over-tightened crank sensor, causing no RPM signal to the computer and shutting down all systems.
- Appreciation expressed to Damian Tedone for assistance.
How to diagnose P2104
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Brief Explanation |
|---|---|
| Clean connections on TAC system | A temporary fix that can improve the issue but may not solve the underlying problem. |
| Inspect throttle pedal assembly | To check for any physical issues that could cause the TAC system to malfunction. |
| Test circuits in TAC system | Ensures that all electrical paths are working correctly, without any breaks or faults. |
| Verify continuity through wiring harness | Confirms that all wires in the throttle system are intact and have a clear electrical path. |
| Consider replacing throttle body assembly | Suggested if the problem persists and wiring is confirmed to be intact, indicating a possible hardware issue with the throttle body. |
| Check for cross-spliced wires | Important in cases where wiring damage is suspected, to ensure no incorrect connections are causing the issue. |
| Ensure proper repair of data lines | Especially critical in modern vehicles with complex electronic systems, to maintain communication between different car parts. |
| Investigate PCM issues | Whether it’s a need for reprogramming or potential hardware damage, the PCM’s role in managing the throttle system is crucial. |
These steps and insights are drawn from real mechanic service cases involving vehicles that exhibited the P2104 code, showcasing the importance of thorough diagnostics and considering all potential issues, from simple connections to more complex system repairs.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko