OBD-II trouble code
U0408: Invalid Data Received From Throttle Actuator A Control Module
A module is receiving messages from the throttle actuator control module, but the data is implausible or out of range. Because throttle control is safety-relevant, the vehicle typically responds with reduced power or limp mode until the data can be trusted again.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $900
- DIY difficulty
- Shop recommended
What does U0408 mean?
Modern engines use electronic throttle control — there is no cable from the pedal to the throttle plate. On most vehicles the engine control module drives the throttle directly, but some designs use a separate throttle actuator control module (or a distinct processing section treated as one on the network) that reads pedal position, commands the throttle motor, and reports throttle plate position back. U0408 sets when a receiving module is still hearing from that throttle actuator controller, but the data in its messages is invalid — reported throttle position out of range, changing implausibly fast, or disagreeing with pedal position and airflow data. The 'A' identifies the primary actuator on engines that may have more than one.
Because an unverified throttle command is genuinely dangerous, electronic throttle systems are built with layered plausibility checks, and their reaction to untrusted data is aggressive: the system typically cuts power, limits throttle opening to a fail-safe angle, or drops into limp mode with a fixed fast idle. Drivers experience this as sudden sluggishness, an unresponsive pedal, or a 'reduced engine power' message. That behavior is by design — the system would rather crawl than accept a throttle value it can't verify.
The causes lean toward whatever corrupts the throttle data at its source: a failing throttle position sensor inside the throttle body, a carbon-fouled throttle plate binding and producing erratic position feedback, degraded pedal position sensors, low system voltage, corrupted or mismatched software, or bus wiring damage. Companion throttle codes (P0120-P0124, P2100-series) usually accompany U0408 and identify the specific circuit — read them first, because they typically name the real problem.
Common causes
- Failing throttle position sensor inside the throttle body assembly
- Carbon buildup causing the throttle plate to bind and report erratic positions
- Degraded accelerator pedal position sensor feeding conflicting data
- Low system voltage or a weak battery/charging system
- Outdated, corrupted, or mismatched throttle/engine control software
- Throttle body or module replaced without required relearn or programming
- Damaged wiring or connectors in the throttle actuator circuit or network bus
- Throttle actuator control module internal fault
Symptoms
- 'Reduced engine power' or similar warning message
- Limp mode: limited throttle response, fixed fast idle, or capped RPM
- Hesitation, surging, or an unresponsive accelerator pedal
- Check engine light with companion throttle codes (P0120-series, P2100-series)
- Symptoms may be intermittent, often worsening as a sensor degrades
- Vehicle usually still moves under its own power, but slowly
Diagnostic steps
- 1.Read ALL stored codes — companion throttle position or actuator codes usually name the specific circuit behind U0408.
- 2.Check battery and charging system voltage; low voltage triggers implausible readings across throttle electronics.
- 3.Compare accelerator pedal position, commanded throttle angle, and actual throttle angle in live data — a mismatch localizes the fault.
- 4.Inspect the throttle body for heavy carbon buildup or binding; clean it and perform the manufacturer's throttle relearn procedure if required.
- 5.Inspect wiring and connectors at the throttle body and pedal for damage, corrosion, or chafing.
- 6.If sensors and wiring check out, verify module software is correct and current before replacing the throttle body or control module, and always complete the relearn after any replacement.
Repair cost
$100 – $900
Throttle body cleaning plus a relearn runs $100-$250 and resolves a surprising share of cases. A replacement throttle body (which includes the position sensors and motor) typically runs $250-$700 installed on mainstream vehicles, more on luxury or performance applications. Pedal sensor assemblies run $150-$400. Software corrections run $100-$300. Skipping the relearn procedure after parts replacement is the most common cause of a repeat visit.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis 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.