OBD-II trouble code
U0406: Invalid Data Received From Fuel Injector Control Module
A module is receiving messages from the fuel injector control module (FICM), but the data is implausible or out of range. Most common on diesels with a dedicated injector driver module. Can cause hard starts, rough running, or reduced power depending on which data is invalid.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $1,400
- DIY difficulty
- Shop recommended
What does U0406 mean?
Some engines — most commonly diesels, along with certain gasoline direct-injection designs — use a dedicated fuel injector control module (FICM) to generate the high-voltage, precisely timed pulses that fire the injectors. The engine control module tells the FICM what it wants; the FICM reports back voltage levels, injector feedback, and fault status over the network. U0406 sets when a receiving module is still hearing from the FICM, but the data in its messages is invalid — out of range, implausible, or inconsistent with other signals. The link is alive; the content is wrong.
On the diesel applications where this code is most familiar, a weak FICM power supply is the classic culprit. The module boosts battery voltage to fire the injectors (48 volts or more on some designs), and as its internal power supply degrades — a well-documented failure on some diesel platforms — the voltage data it reports drifts out of the plausible range while injector performance suffers. Low battery voltage, corroded FICM connectors, excessive heat exposure, and corrupted or mismatched module software produce the same signature. As always with invalid-data codes, U0406 frequently arrives with companions — injector circuit codes or FICM performance codes that name the specific failure.
Symptoms track the underlying cause rather than the network complaint itself: hard starting (especially cold on diesels), rough idle, misfires, reduced power, or a no-start in severe cases. The vehicle usually remains driveable while the fault is intermittent, but a failing FICM tends to get worse, and prolonged rough running is hard on the rest of the engine — this one deserves prompt diagnosis.
Common causes
- Degraded FICM internal power supply reporting out-of-range voltage (classic diesel failure)
- Low battery voltage or a weak charging system, especially during cold-weather cranking
- Corroded or damaged FICM connectors and wiring
- Outdated, corrupted, or mismatched FICM software
- FICM replaced without proper programming
- Heat damage to the module (often mounted on or near the engine)
- Companion injector circuit fault producing the invalid values
- Bus wiring problems corrupting messages in transit
Symptoms
- Hard starting, especially cold starts on diesels
- Rough idle or misfiring
- Reduced engine power or hesitation under load
- Check engine light with companion injector or FICM codes
- No-start in severe cases
- Symptoms often worse in cold weather when voltage demands peak
- Vehicle generally still driveable while the fault is intermittent
Diagnostic steps
- 1.Read ALL stored codes — companion injector circuit or FICM performance codes usually identify the specific failure.
- 2.Test battery and charging system health first; weak cranking voltage aggravates and can mimic FICM faults.
- 3.On diesels, measure the FICM's output voltage with a scan tool or meter during cranking and running — a sagging supply confirms the classic power-supply failure.
- 4.Inspect FICM connectors and wiring for corrosion, chafing, and heat damage.
- 5.Verify the FICM has correct, current software, especially after any module replacement.
- 6.Confirm the diagnosis before replacing hardware — repair services and rebuilt FICMs are widely available for common diesel applications at well below new-module cost.
Repair cost
$100 – $1,400
A reflash or software correction runs $100-$300, and battery/charging repairs $150-$600. The big-ticket outcome is FICM replacement on diesel applications: rebuilt or repaired units typically run $300-$800 installed, while new OEM modules with programming can reach $900-$1,400. Fixing weak batteries first is essential — replacing a FICM while undersized cranking voltage persists invites a repeat failure.
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.