Code
P1173
FIAT
P — Powertrain
Mixture 1 strength (additive) fault | Mixture 1 ratio fault | Self-adaptive parameter FRA fault
Views:
UK: 12
EN: 27
RU: 25
AI status
Completed
Completed
100%
Causes
- Air/fuel mixture too lean or too rich over extended time causing adaptive trim to exceed limits
- Faulty or slow oxygen (lambda) sensor or sensor heater
- Mass airflow (MAF) or MAP sensor inaccurate
- Fuel delivery problems (low/high fuel pressure, clogged injectors)
- Vacuum or intake air leaks downstream of the MAF
- Faulty wiring/connectors or poor grounds to sensors or ECU
Symptoms
- Check Engine Light (MIL) illuminated
- Poor fuel economy
- Rough idle or hesitation on acceleration
- Hard starting or unstable idle after start
- Increased tailpipe emissions
- Occasional surging or stumbling under load
What to check
- Connect a capable scan tool and read pending/confirmed codes and freeze frame data
- Monitor live data: long‑term fuel trim (FRA/LTFT), short‑term fuel trim (STFT), O2 sensor voltages, MAF/MAP, fuel rail pressure
- Perform a visual inspection of intake hoses, vacuum lines, and intake manifold gaskets
- Inspect wiring and connectors for corrosion, breaks, or poor grounds at sensors and ECU
- Perform a smoke test to locate intake or vacuum leaks
- Measure fuel rail pressure at idle and under load and compare to spec
Signal parameters
- Long‑term fuel trim (LTFT / FRA) — abnormal if persistently outside about ±10–15%
- Short‑term fuel trim (STFT) — quick corrections around zero during transitions
- O2 (lambda) sensor bank 1 voltage and switching frequency (typical 0.1–0.9 V, switching regularly)
- MAF sensor airflow (g/s) or voltage vs RPM and commanded load
- MAP sensor pressure (kPa) correlated to rpm/throttle position
- Fuel rail pressure (bar/psi) steady and within manufacturer specification
Diagnostic algorithm
- Retrieve all codes and freeze frame, note operating conditions when P1173 set.
- Clear codes, start engine and monitor LTFT/FRA, STFT, O2 voltages, MAF and fuel pressure at idle and under steady acceleration.
- If LTFT/FRA is high (lean) or low (rich), perform a smoke or pressure leak test of the intake and vacuum system to find unmetered air.
- Inspect and test MAF sensor (clean if contaminated, follow manufacturer procedure) and verify airflow values vs expected for RPM/load.
- Test O2 sensor(s) for proper heater operation and switching response; replace if slow or out of range.
- Measure fuel rail pressure and inspect fuel pump, pressure regulator and filter; perform injector balance/flow test if needed.
- Check wiring and connectors for sensors (MAF, O2, MAP, fuel pressure) and repair any damage or poor grounds.
- If components test good, clear learned fuel trims (per service procedure) and perform drive cycles to allow relearning; monitor for recurrence.
- Consult manufacturer technical bulletins or update ECU software/calibration if recurrent or unexplained.
- Replace failed components only after confirming with testing; retest and verify adaptive trims return to normal range.
Likely causes
- Intake manifold gasket leak or vacuum hose disconnected/cracked
- Contaminated or failing O2 sensor (bank 1)
- Dirty or faulty MAF sensor (incorrect airflow reading)
- Weak fuel pump, leaking fuel pressure regulator or clogged fuel filter
- One or more fuel injectors partially clogged or leaking
- Damaged wiring or connector to O2/MAF/fuel pressure sensors
Fault status
Status
P1173 - Mixture 1 strength (additive) fault / Self‑adaptive parameter FRA out of range (fuel trim adaptation fault)
Repair difficulty: Medium
Diagnostic time: 0.5 - 3.0 hours
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