What this code means
P1109 may indicate the ECM/PCM is seeing the BARO sensor circuit as out of range.
What the vehicle may do
- The vehicle may run normally even when the code is stored.
- The vehicle can have possible drivability complaints depending on when the fault occurs.
- The concern may appear intermittently.
Possible fault areas
- Possible BARO signal concern
- Possible wiring or connector issue
- Possible ECM/PCM software or module-related concern
Diagnostic path
Opening context
On this 2010 to 2017 Honda Accord with the 2.4 gas engine, P1109 points to the BARO sensor circuit being out of range. In plain terms, the computer may be seeing a barometric pressure signal that does not make sense. The vehicle may run normally, or it can have drivability complaints depending on when the fault shows up. Broadly, this can involve a possible signal issue, wiring or connector concern, or a PCM software or module-related problem. Before getting into the test path, record the freeze data and any on-board snapshot information, then start with the basic system checks and follow a structured diagnostic approach.
Problem verification
Start by turning the ignition switch to ON (II). Clear the DTC with the HDS, then check Pending or Confirmed DTCs with the HDS. At this point, the question is simple: does P1109 come back as indicated or not?
Result of the verification check
If P1109 is indicated again, the failure is duplicated. From there, update the PCM if it does not have the latest software, or substitute a known-good PCM, then move into verifying the repair. If P1109 is not indicated, treat it as an intermittent failure, and the system is okay at this time.
Verify the repair
To verify the repair, check Pending or Confirmed DTCs again with the HDS. If P1109 is still indicated and the PCM was updated, substitute a known-good PCM, then recheck. If the PCM was already substituted, go back to the beginning of the diagnostic path and repeat the verification process instead of guessing.
Completion decision
If P1109 is not indicated during repair verification, the next step depends on what was done. If the PCM was updated, troubleshooting is complete. If a known-good PCM was substituted, replace the original PCM. If other Pending or Confirmed DTCs are present, check what they mean next and follow the appropriate diagnostic path for those faults.
Takeaway
The key with P1109 on this Accord is to verify whether the code actually returns after clearing it, then separate an intermittent condition from a duplicated fault before making a PCM decision. For more diagnostic training, visit stepdiagnostics.com.
Final check
P1109 often requires confirming whether the fault duplicates after clearing before deciding whether the issue is intermittent or needs the PCM-focused verification path.
For more guided automotive diagnostics, visit STEP Diagnostics.
