Invalid Data Received From Alternative Fuel Control Module
The U0409 code means the vehicle's onboard diagnostic system has detected: Invalid Data Received From Alternative Fuel Control Module. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $50 - $500 (usually the fault behind the bad data, not the network itself)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine or related warning light on
- Functions relying on data from the Alternative Fuel Control Module may act erratically
- Often intermittent
Probable Causes (Ranked by Likelihood)
- The Alternative Fuel Control Module is transmitting, but its data is implausible - often a failing sensor feeding it High
- Intermittent wiring fault corrupting messages Moderate
- Software mismatch after service Moderate
- Failing Alternative Fuel Control Module Low
Frequently Asked Questions
What does U0409 mean?
U0409 means this module IS communicating with the Alternative Fuel Control Module, but the data it sends fails plausibility checks. Diagnose the source module first.
Can I keep driving with U0409?
Usually yes for a short period. The affected function may be degraded, and intermittent wiring faults tend to worsen - diagnose soon.
Should I replace the module for U0409?
Not first. Most communication codes are power, ground, fuse, or wiring problems. Replace the module only after those test good - modules are expensive and often require programming.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Scan the Alternative Fuel Control Module itself - the invalid data usually traces to a fault code stored there.
-
Fix any codes in the source module first; this code often clears with them.
-
Check for recent programming or battery-disconnect events.
-
If the source module is clean, monitor the specific data value flagged and follow the OEM pinpoint test.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- All OBD-II vehicles - network (U) codes are standardized across makes
Related Codes
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.