Code
P1143
CHRYSLER
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 17
EN: 30
RU: 19
AI status
Completed
Completed
100%
Causes
- Failed or degraded Bank 1 Sensor 3 oxygen sensor
- Open, shorted, corroded or damaged sensor wiring or connector
- Exhaust leak upstream of the sensor
- Vacuum leak causing a lean condition
- Low fuel pressure, clogged injector or fuel delivery issue
- Contaminated sensor (oil, coolant, silicone, leaded fuel)
Symptoms
- Check Engine Light (MIL) illuminated
- Possible poor fuel economy or drivability issues
- Failed emissions test (high tailpipe O2/HC/NOx)
- Possible rough idle, hesitation or stumble under load (if lean condition is actual)
- Downstream O2 sensor voltage low or flatlined on live data
What to check
- Read freeze frame and all stored codes; note conditions when code set
- Scan live data: compare Bank 1 Sensor 3 voltage to upstream sensor(s) and observe fuel trims
- Inspect sensor wiring and connector for corrosion, breaks, pin push-out or heat damage
- Check for exhaust leaks upstream of the sensor (visual, smoke or audible)
- Perform a vacuum leak check (smoke or pressure test)
- Verify fuel pressure and fuel delivery under load
Signal parameters
- Narrowband zirconia O2 sensors typically produce ~0.1–0.9 V (lean to rich); downstream sensors often sit more stable near ~0.4–0.6 V when cat is working
- A persistent low/near-zero voltage from the sensor indicates a lean reading or open sensor circuit
- Heater circuit should see battery voltage supply; heater resistance varies by sensor (verify manufacturer specs)
- Compare Sensor 3 waveform and level to Bank 1 Sensor 1 (upstream) — downstream should not mirror rapid switching if catalytic converter is functioning
Diagnostic algorithm
- Verify the code with a scan tool and review freeze-frame data. Check for related codes (heater, fuel trim, upstream O2).
- Visually inspect the Bank 1 Sensor 3 connector and wiring harness for damage, corrosion, pin push-out or mating issues. Repair as needed.
- Back-probe the sensor connector and monitor voltage while engine is warmed. Note if voltage is low/flat or fluctuating. Compare to upstream sensor.
- Check heater circuit: measure resistance across heater terminals and verify supply voltage and ground switching from PCM.
- Inspect for/exclude exhaust leaks upstream of the sensor and perform intake vacuum/leak test to rule out unmetered air.
- Check fuel system: test fuel pressure and inspect injectors for flow; inspect MAF/MAP for correct operation and signals.
- If wiring and supporting systems are good but sensor still reads low, replace Bank 1 Sensor 3 with a correct OEM or equivalent sensor.
- Clear codes and perform a road/drive cycle while monitoring O2 voltages and fuel trims to confirm repair. If code returns, continue diagnosing PCM or catalytic converter as needed.
Likely causes
- Contaminated or failed downstream oxygen sensor
- Damaged wiring or poor connector contact at sensor
- Exhaust or intake vacuum leak creating real lean condition
- Fuel pressure low or injector problem
- Sensor heater circuit fault (if sensor not at operating temperature)
Fault status
Status
HO2S Bank 1 Sensor 3 — lean or low voltage detected. PCM sees lower-than-expected oxygen sensor voltage at Bank 1 Sensor 3. Inspect sensor, wiring, exhaust and fuel/air systems; repair as required.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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