Code
P1175
ALFA ROMEO
P — Powertrain
Mixture 2 strength (multiplicative) fault
Views:
UK: 16
EN: 29
RU: 28
AI status
Completed
Completed
100%
Causes
- Vacuum or intake leak on bank 2
- Faulty or out-of-spec oxygen (lambda) sensor on bank 2
- Faulty mass air flow (MAF) or manifold absolute pressure (MAP) sensor
- Clogged or leaking fuel injector(s) on bank 2
- Low or fluctuating fuel pressure
- Damaged wiring or poor connector to O2 sensor, MAF/MAP, or injectors
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or unstable idle speed
- Loss of power, hesitation, or stumbling under load
- Increased fuel consumption (running rich) or increased emissions (running lean)
- Failed emissions test or lambda regulation out of range
What to check
- Read stored freeze-frame and pending codes with a capable scanner
- Check live data: short-term and long-term fuel trims for both banks, O2 sensor voltages and switching, MAF/MAP readings
- Visually inspect vacuum lines, intake gaskets and PCV system for leaks
- Inspect wiring and connectors to O2 sensors, MAF/MAP sensors and fuel injectors for damage or corrosion
- Measure fuel rail pressure and compare to specification
- Perform smoke test for intake leaks if available
Signal parameters
- Long-term fuel trim (LTFT) bank 2: should typically be within ±10% (manufacturer-specific limits)
- Short-term fuel trim (STFT) bank 2: rapid corrections around 0% during closed loop
- O2 (lambda) sensor voltage bank 2 (narrowband): switches ~0.1–0.9 V when healthy
- HEGO switching frequency: regular switching when in closed loop
- MAF: airflow vs engine speed typical curve (no sudden jumps)
- Fuel rail pressure: within manufacturer specified PSI/bar with key on and under load
Diagnostic algorithm
- Connect scan tool and record freeze frame and live data for LTFT/STFT, O2 voltages, MAF/MAP and fuel pressure
- Confirm the code is P1175 and note any additional related DTCs (O2 sensors, fuel system, MAF)
- Attempt to reproduce fault with road test while monitoring live parameters
- Visually inspect intake, vacuum hoses, intercooler piping (if present) and intake manifold for leaks or damage; repair any found
- Perform a smoke test of intake and vacuum system if a leak is suspected
- Check fuel pressure at the rail (static and under load) and compare with spec; inspect fuel filter and supply
- Inspect and test the MAF sensor; clean using approved MAF cleaner if dirty and retest
- Probe O2 sensor (bank 2) signal and heater circuit: verify switching behavior and proper voltage; replace sensor if slow, stuck or out of spec
- Inspect wiring and connectors for damaged insulation, corrosion, or poor ground; repair as necessary
- If injectors are suspected, perform balance or flow testing on bank 2 injectors; clean or replace faulty injectors
- After repairs, clear codes and perform verification drive cycle to confirm the adaptive multiplicative correction returns to normal range
- If all sensors and actuators check OK and problem persists, consider ECU software update or ECU diagnosis at dealer level
Likely causes
- Vacuum leak or intake manifold gasket leak on bank 2
- O2 (lambda) sensor on bank 2 out of range or slow response
- MAF sensor dirty or faulty causing incorrect air measurement
- Leak or low fuel pressure reducing injector flow
Fault status
Status
Mixture strength (multiplicative) fault detected on bank 2. ECU adaptation exceeded permissible limits — check sensors, wiring, fuel delivery and intake for faults.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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