What this code means
The PCM may be seeing the two intake air temperature inputs disagree after start-up.
What the vehicle may do
- The vehicle may have a warning light.
- The vehicle can have little or no obvious drivability change.
- Start-up conditions may be important for when the fault is detected.
Possible fault areas
- Possible intake air temperature signal issue.
- Possible sensor-related concern in the intake air temperature comparison.
- Possible connector security or terminal fit concern at the involved sensors.
Diagnostic path
Opening context
On a 2016-2024 Honda Civic with the 1.5 turbo, P2199 is an intake air temperature correlation code. In plain language, the PCM may be seeing IAT sensor 1 and IAT sensor 2 disagree after start-up. The vehicle may simply have a warning light, and it can have little or no obvious drivability change. For this fault, keep your thinking around the intake air temperature signal inputs, the sensors involved, connector security, and terminal fit. Before getting into the targeted checks, start with the basic system checks and follow a structured diagnostic approach.
Reproduce the operating conditions
To run the confirmation routine for P2199, turn the vehicle to the OFF (LOCK) mode and leave it there for at least 6 hours. After that soak period, start the engine and let it idle for at least 10 seconds. This puts the system back into the start-up condition where the PCM compares the two intake air temperature signals.
Check the connection points
After the operating conditions are reproduced, move to the connector and terminal check. Check for a secure connection and for loose terminals at ECT sensor 1, ECT sensor 2, the MAF sensor and IAT sensor 1 assembly, and IAT sensor 2. At this point, do not jump past the basics; connector security and terminal fit have to be known good before you trust the branch result.
Use the branch result
If the connector or terminal condition is abnormal, the diagnostic direction is a connection or terminal problem. If the connections and terminals are normal, the diagnostic path identifies IAT sensor 2 as the problem area. If what you see does not line up with that path, pause, recheck the earlier diagnostic path, and avoid guessing.
Closing takeaway
The takeaway is simple: P2199 is a comparison fault between the two intake air temperature inputs after start-up. Reproduce the soak and idle conditions, check the listed connectors and terminals carefully, and let the branch result guide the next move. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code often needs a careful comparison-focused diagnosis rather than guessing at parts.
For more guided automotive diagnostics, visit STEP Diagnostics.
