Code
P1176
FIAT
P — Powertrain
Mixture 2 strength (additive) fault
Views:
UK: 7
EN: 12
RU: 6
AI status
Completed
Completed
100%
Causes
- Faulty additive dosing pump or metering valve (dosing unit failure)
- Clogged or contaminated additive lines or injector/nozzle
- Low or contaminated additive reservoir (level/quality issue)
- Faulty additive concentration sensor or related lambda/strength sensor
- Wiring faults: open, short to ground/voltage, or high resistance in harness/connectors
- Poor ground or supply voltage to dosing components or sensors
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Poor running on affected bank (misfire, rough idle)
- Reduced engine performance or hesitation under load
- Increased emissions or failed emissions test
- Unusual exhaust odor or black smoke (if mixture excessively rich)
- Possible limp-home mode on some vehicles
What to check
- Read stored trouble codes and freeze-frame data with a capable scan tool (manufacturer-level preferred)
- Check additive tank level and condition; inspect for contamination
- Visual inspection of dosing pump, lines, filters and injector/nozzle for blockages or leaks
- Inspect wiring and connectors for damage, corrosion, loose pins, and proper sealing
- Measure power and ground at dosing pump/valve and at the sensor(s)
- Monitor live data: additive strength sensor, lambda sensors, long-term fuel trim (LTFT) and short-term fuel trim (STFT) bank 2
Signal parameters
- Expected lambda sensor voltage swings ~0.1–0.9 V (or reported lambda) for Bank 2 O2 sensor
- Fuel trim values: STFT typically within ±10%; LTFT generally within ±10% (significant deviation on bank 2 indicates issue)
- Dosing pump supply voltage ~12 V when commanded; measured current draw within manufacturer spec
- Additive sensor signal voltage/resistance per manufacturer specification (consult service data)
- Commanded dosing duty cycle or pulse count vs. actual feedback (flow or concentration) difference
Diagnostic algorithm
- Connect a scan tool, record all stored codes and freeze-frame data; note conditions when fault set.
- Verify additive tank level and condition. Refill with correct additive if low and clear code to retest.
- Visually inspect dosing pump, lines, filters and nozzle for blockages, kinks, leaks or contamination.
- With ignition on, check for battery voltage at dosing pump and a good ground. Backprobe connector while commanding pump ON; verify operation and current draw.
- Inspect and wiggle wiring harness and connectors while monitoring live data for intermittent faults.
- Monitor bank 2 lambda and fuel trim values during idle and load. If lambda is stuck or trims are extreme, isolate sensor vs. delivery problem.
- If actuator tests available, command dosing unit and verify measurable change in additive flow/concentration or lambda response; if no response, suspect dosing unit or wiring.
- If dosing pump and wiring pass, test additive concentration sensor or bank 2 strength sensor per manufacturer procedures (voltage/resistance or bench test).
- Clean or replace clogged nozzles/filters and replace defective dosing pump, valve or sensor as needed.
- After repair, clear codes and perform drive cycle to confirm fault does not return; re-check fuel trims and emissions parameters.
Likely causes
- Failed/weak dosing pump or solenoid preventing correct additive delivery
- Blocked dosing nozzle or filter reducing flow
- Damaged sensor on bank 2 (additive strength or lambda) providing incorrect feedback
- Connector corrosion or intermittent wiring underhood causing signal loss
- Empty or degraded additive tank causing out-of-spec mixture
Fault status
Status
MIL illuminated. ECU detected additive/mixture strength on bank 2 outside expected parameters or failure of additive dosing/feedback circuit. Code stored with freeze-frame data.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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