OBD-II trouble code
P2108: Throttle Actuator Control Module Performance
The powertrain control module is watching the throttle actuator control module from the outside and does not like what it sees. The signals coming back are missing, delayed, or implausible — so the module's behavior, not its wiring, is what has been flagged.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air Metering
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $150 – $1,400
- DIY difficulty
- Shop recommended
What does P2108 mean?
On a drive-by-wire vehicle the throttle actuator control function and the rest of the powertrain control strategy check up on each other constantly. The powertrain control module sends a throttle request, and it expects a specific pattern of acknowledgement and feedback in return within a specific window of time. P2108 sets when that expectation is not met — the response is absent, arrives too late, or contains a value that does not make sense for what was asked.
The useful way to hold this code is as the outside view of the same module that P2107 reports on from the inside. P2107 is the throttle processor raising its own hand and saying its self-check failed. P2108 is the powertrain control module saying the throttle actuator control module is not behaving correctly, without knowing why. Both codes very often appear together, and neither one identifies a specific broken wire — that is what the circuit codes at P2100, P2102 and P2103 are for.
What makes P2108 worth diagnosing carefully rather than treating as a module replacement is that a performance code is precisely the outcome you get from marginal conditions rather than from clean failures. A module running on a sagging battery responds sluggishly. A module with a resistive ground computes and communicates unreliably. A charging system with failing diodes injects AC ripple that corrupts communication between modules. In every one of those cases the module's performance genuinely is wrong, exactly as the code says, and the module itself is perfectly good. This is why power quality and ground integrity come before parts, and why a shop that quotes a module off the code alone has skipped the part of the job that actually saves you money.
Architecture matters here as much as it does for P2107. Some vehicles have a physically separate throttle actuator control module, typically near the throttle body or in an under-hood electrical center; others carry the function inside the powertrain control module. On the separate-module vehicles the communication path between the two modules — its wiring, its connectors, and the bus it rides on — becomes a real suspect. On the integrated vehicles there is no external path to fault, which narrows the diagnosis to power, grounds, and software.
Because the powertrain control module cannot rely on a throttle system it cannot verify, it withdraws authority: expect reduced power, a forced idle, an RPM cap, or in some cases a no-start, along with a fail-safe code from the P2104 / P2105 / P2106 / P2110 group stored alongside this one.
Common causes
- Weak or failing battery causing sluggish or unreliable module operation
- Failing alternator producing excessive AC ripple that corrupts inter-module communication
- Corroded, loose, or high-resistance module or engine ground
- Damaged, chafed, or shorted wiring between the powertrain control module and the throttle actuator control module
- Corroded connector or backed-out pin at either module
- Water intrusion into the throttle actuator control module or its connector
- Internal failure of the throttle actuator control module
- Internal failure of the powertrain control module (rare — rule out everything else first)
- Outdated or corrupted module software; some platforms have a service bulletin reflash for this exact code
- Aftermarket alarm, remote start, performance tune, or accessory wiring spliced into throttle or module circuits
- Failed throttle body assembly loading the actuator circuit enough to skew module behavior
- Blown fuse or failed relay in the module's power feed
Symptoms
- Check engine light on, generally with a reduced-power or wrench warning
- Reduced engine power or limp mode
- Engine cranks but will not start
- Poor or absent throttle response — the pedal moves and nothing happens
- Hesitation, surging, or stalling
- Rough idle or an idle that hunts
- Multiple codes from unrelated systems stored at the same time
- A fail-safe code from the P2104 / P2105 / P2106 / P2110 group, and frequently P2107, stored alongside it
Diagnostic steps
- 1.Scan every module and record all stored and pending codes with freeze frame data. Note whether P2107 is present — the pair together confirms the fault is at the module level rather than out in the throttle body.
- 2.Establish from service data whether your vehicle has a standalone throttle actuator control module or performs the function inside the powertrain control module. This determines whether there is a communication path to test at all.
- 3.Load-test the battery and inspect the terminals, cables, and ground straps. A performance code is exactly what marginal voltage produces, and this is the cheapest thing that can be wrong.
- 4.Test the charging system for output and for AC ripple. Failing alternator diodes corrupt module-to-module communication and produce intermittent performance faults on healthy hardware.
- 5.Perform voltage-drop tests on the module grounds with the engine running rather than relying on a static continuity check.
- 6.Verify power at the module connector with the key on, and check the relevant fuses and relays.
- 7.On vehicles with a separate module, check the wiring between the two modules for continuity, shorts to power, shorts to ground, and shorts between circuits, with both ends disconnected.
- 8.Inspect both module connectors closely for corrosion, moisture, spread or backed-out terminals, and properly seated locking tabs.
- 9.Check for a manufacturer service bulletin and a software update covering this code. A reflash is a documented fix on several platforms and is far cheaper than a module.
- 10.Compare commanded and actual throttle position in live data while sweeping the pedal, to establish whether the throttle body itself is responding correctly and separate a module fault from a mechanical one.
- 11.Only after power, grounds, wiring, connectors, and software have all been addressed should a module be replaced. Plan on programming to the vehicle, a throttle relearn, and on some platforms an immobilizer relearn as well.
Repair cost
$150 – $1,400
The cheap outcomes are real and common: a battery, a repaired ground, a cleaned connector, a wiring repair, or a charging system fault, generally $150-$500 including diagnostic time. A software reflash where a bulletin covers the code typically runs $100-$250 at a dealer. A standalone throttle actuator control module is roughly $250-$700 for the part, landing near $400-$900 installed with programming. Replacing an integrated powertrain control module is the top of the range at $500-$1,400 or more installed, because it must be programmed and often relearned to the immobilizer. Expect a meaningful diagnostic charge and treat it as insurance against buying the most expensive part on the list for a ground problem.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with control module replacement & programming preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.