OBD-II trouble code
U0338: Software Incompatibility With Remote Function Actuation Module
A module has detected that the remote function actuation (RFA) module — which handles keyless entry, key fob commands, and often remote start and passive entry — is running software or a calibration that doesn't match the rest of the vehicle's modules. It's a programming mismatch, not a wiring fault, usually following a module replacement, update, or reflash.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $120 – $450
- DIY difficulty
- Shop recommended
What does U0338 mean?
U0338 sets when a module on the vehicle network determines that the remote function actuation (RFA) module is running a software or calibration version that is incompatible with the version-matched set the rest of the vehicle expects. The RFA module is responsible for receiving and validating signals from key fobs and interpreting requests like lock/unlock, remote start, panic alarm, trunk release, and, on many vehicles, passive keyless entry and push-button start authorization. Because it plays a role in verifying that a valid key is present before allowing the vehicle to start, its software is coordinated closely with the body control module and, on many vehicles, the immobilizer/security system. When the RFA module's software doesn't fit that coordinated set, U0338 is stored — the module is still communicating, but its programming disagrees with what the rest of the vehicle expects it to be running.
The cause is almost always service-related and centered on the RFA module. It was replaced and not programmed with the correct VIN-specific software, a used unit was installed without being re-learned to this vehicle, a software update was applied to the body control module or immobilizer but not the RFA module, or a reflash was interrupted or used the wrong calibration file. Because the underlying issue is data rather than a failed antenna, receiver, or wiring harness, chasing it electrically leads nowhere — the fix is reprogramming the RFA module to a matching, manufacturer-approved software set, followed by re-learning the vehicle's key fobs if needed.
Most of the time, a software mismatch in the RFA module affects convenience functions — remote start not working, key fob range being reduced, or lock/unlock commands being unreliable — which is why this is generally rated medium rather than high severity. However, because this module can be tied into start authorization on some vehicles, a mismatch occasionally causes no-start or intermittent starting complaints, which pushes the practical urgency higher even though the base severity classification stays medium. Any no-start or intermittent-start symptom alongside U0338 should be prioritized and diagnosed by a technician right away.
Common causes
- RFA module replaced without correct VIN-specific programming
- A used or salvage-yard RFA module installed without being re-learned to this vehicle
- Body control module or immobilizer software updated but the RFA module's calibration left out of step
- An interrupted or incomplete RFA module reflash
- Key fobs not re-learned/re-paired after RFA module programming
- Reprogramming done with the wrong calibration file or region/security variant
Symptoms
- Warning message and a stored U0338 (often alongside other U03xx or security-related codes)
- Key fob commands (lock, unlock, remote start, trunk release) working intermittently or not at all
- Reduced key fob range
- Passive entry or push-button start behaving inconsistently on equipped vehicles
- Occasional no-start or delayed-start complaints on vehicles where RFA ties into start authorization
- Condition typically appears right after an RFA module replacement, update, or reflash
Diagnostic steps
- 1.Confirm the recent history — U0338 almost always follows an RFA module replacement, software update, or reflash; identify what was serviced.
- 2.Scan all modules and read the RFA module's software/calibration part number; compare against the manufacturer's current approved set for the VIN.
- 3.Note any companion codes from the body control module, immobilizer, or security system that help confirm the RFA module is the mismatched unit.
- 4.Verify the module was programmed with correct VIN-specific software, not generic or wrong-vehicle data.
- 5.Reprogram/reflash the RFA module to the matching, up-to-date calibration using a manufacturer-approved tool.
- 6.Re-learn/re-pair all key fobs to the vehicle after reprogramming.
- 7.Clear the codes and confirm U0338 does not return and that all remote functions and starting work reliably after a full key cycle.
Repair cost
$120 – $450
This is primarily a programming fix. Reprogramming the RFA module typically runs $120-$300, plus a small additional charge to re-learn key fobs; costs run up to $450 when dealer-only calibrations or a full security-system re-sync are required. If the module was wrongly replaced, sourcing a correct one is a separate cost; U0338 itself is usually resolved by correct reprogramming.
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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.