What it means
The vehicle bus reports loss of communication with the EVAP leak detection module. Tank-pressure / vacuum diagnostics for fuel-vapour leaks cannot be commanded.
At a glance
- Usually lights the warning light of the system that lost communication
- Affects emissions; the car can fail an emissions test
How it works
The evaporative-emissions leak detection control module runs or supports checks that use fuel-tank pressure or vacuum to find vapour leaks. U029F sets when the vehicle network stops receiving messages from that module, so those leak-detection checks cannot be commanded normally.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and capture freeze-frame data and related EVAP codes to determine whether the leak detection module is the only device with communication loss.
- Check 12-V supply condition and scan-tool module status, since low voltage can prevent the EVAP module from responding.
- Inspect the leak detection module's accessible connector and bus wiring for damage, moisture, corrosion, or a loose fit.
- Check the module's power and ground circuits under load using the vehicle wiring information and manufacturer's specification.
- Test the communication circuit for opens, shorts, or poor connections before concluding the leak detection module itself has failed.
Common fixes
- Repair a loose, corroded, or moisture-damaged connector at the leak detection module.
- Repair an open or short in the module's bus wiring.
- Restore a faulty power or ground connection to the module.
- Replace the EVAP leak detection control module if its circuits are sound but it does not communicate.
Can I keep driving?
If the vehicle runs normally and there is no fuel leak or strong fuel smell, this fault usually does not affect immediate drivability; schedule repair so fuel-vapour leak checks can resume. Stop and address any actual fuel leak or strong fuel vapour smell promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.