P1123moderate severityPowertrain
Long Term Fuel Trim Mixture Too Rich
on 2010 Kia Forte 2.4L I4 · FWD
What this code means
The PCM has detected that the long-term fuel trim is correcting excessively in the lean direction, indicating the engine is running too rich. The fuel system is consistently delivering more fuel than needed.
Symptoms
- Check Engine Light
- Poor fuel economy
- Black smoke from exhaust
- Rough idle
- Fouled spark plugs
Common causes
- Leaking fuel injector
- High fuel pressure (faulty regulator)
- Faulty oxygen sensor reading lean incorrectly
- Saturated charcoal canister purging fuel vapor
- Coolant temperature sensor reading cold
Diagnostic steps
- Check long-term fuel trim values on scan tool (excessively negative indicates rich correction)
- Check fuel pressure with gauge
- Inspect spark plugs for rich fouling
- Test O2 sensor operation
- Check for leaking injectors
Repair notes
Correct the root cause of the rich condition, typically a leaking injector or faulty fuel pressure regulator.
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Bluetooth code reader (~$25)
Veepeak OBDCheck BLE →
Pairs with your phone — reads and clears codes, live data.
Serious DIY (~$100)
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
Shop-grade tablet (~$300+)
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
As an Amazon Associate, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1