Your car's computer says "Go," but the throttle says "No." P2108 means there is a lag or error in throttle movement. Learn how to compare the "Command" vs. "Actual" data wirelessly.
1. What Does P2108 Mean?
The code P2108 stands for "Throttle Actuator Control (TAC) Module Performance."
Modern vehicles rely on Electronic Throttle Control (ETC), meaning there is no cable connecting your foot to the engine. When you press the pedal, the ECU commands an electric motor to open the butterfly valve.
P2108 is a "Disagreement" code. The ECU sends a command (e.g., "Open 20%"), but the feedback it gets from the sensors shows something different (e.g., "Only open 10%" or "Moving too slowly"). The module's performance is not meeting the target.
2. Processor vs. Performance
It's easy to confuse P2108 with other similar codes. Here is the difference:
| Code | Issue Type | Meaning |
|---|---|---|
| P2107 | Processor Error | The ECU's internal "brain" failed a self-test (often low voltage). |
| P2108 | Performance | The ECU is fine, but the Throttle Body isn't reacting correctly to commands. |
| P2101 | Range | The motor is working, but the valve is physically stuck or out of range. |
3. Why Is the Throttle Lagging?
🐢 Limp Mode Warning
If the ECU cannot trust the throttle position, it will restrict your speed (Limp Mode) or force the engine to idle to prevent accidents. You may feel a sudden loss of power.
P2108 is usually caused by physical resistance or electrical resistance:
- Carbon Buildup (Most Common): A ring of sticky black sludge builds up around the throttle plate. This creates friction, causing the motor to move slower than the ECU expects.
- Weak Throttle Motor: The electric motor inside the unit is wearing out and can't push the plate open fast enough.
- High Resistance in Wiring: Corrosion on the connector pins creates "electrical friction," weakening the signal to the motor.
4. Diagnosis: Wireless Data Comparison
To confirm P2108, you need to see the "disagreement" happening in real-time. The iCarsoft CR MAX BT (Bluetooth) allows you to graph two data streams simultaneously to spot the lag.
Step 1: Setup the Comparison
- Plug in the Bluetooth dongle and take the 7-inch tablet.
- Go to Live Data. Select two specific items:
- APP / Throttle Command (What the ECU wants)
- TP / Throttle Position Actual (What the valve is doing)
- Merge Graph: Combine them into one graph.
Step 2: The Snap Test
- With the engine OFF but Ignition ON:
- Press the gas pedal quickly and release it.
-
Analyze: The two lines should move in perfect sync.
- P2108 Issue: You will see the "Actual" line lagging behind the "Command" line, or failing to reach the peak. This confirms the Throttle Body is sticking or failing.
Step 3: Visual Check
- Remove the air intake hose. Inspect the metal plate. If it's black and gummy, clean it with throttle body cleaner and a rag. This fixes P2108 in 50% of cases!
See the Lag, Fix the Drag
The iCarsoft CR MAX BT makes advanced diagnostics accessible. Its ability to graph "Command vs. Actual" data wirelessly lets you diagnose performance issues without expensive dealer tools.
- Multi-Graphing: Compare throttle targets vs. reality.
- Wireless Bluetooth: Perform tests from under the hood.
- Throttle Relearn: Reset the idle after cleaning.
Shop CR MAX BT
6. Frequently Asked Questions
Q: I cleaned the throttle body but the code came back. Why?
A: Did you perform a relearn? After cleaning, the airflow changes significantly. You must use the CR MAX BT to perform a "Throttle Body Adaptation" (Idle Relearn) so the ECU knows the new airflow characteristics.
Q: Can I drive with P2108?
A: It's unsafe. The throttle response will be unpredictable, and the car may suddenly enter Forced Idle (P2104) while driving, leaving you without power in traffic.
Q: Is the TAC module separate from the ECU?
A: On older cars (early 2000s GM/Chevy), yes, there was a separate TAC module box. On most modern cars (2006+), the TAC module is integrated directly into the main ECU (PCM).
