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Home / DTC / P1157 — Lack of Downstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2

P1157 — Lack of Downstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2

Detailed page for trouble code P1157.

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Code

P1157

LINCOLN P — Powertrain

Lack of Downstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2

Brand: LINCOLN
Type: P — Powertrain
AI status
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ready
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Page language: EN

Causes

  • Faulty downstream heated oxygen sensor (Bank 2, Sensor 2)
  • Open/short or poor connector in sensor signal or heater circuit
  • Exhaust leak upstream of the downstream sensor
  • Intake vacuum leak or unmetered air
  • Low fuel pressure or weak fuel pump/clogged filter
  • Faulty MAF/MAP or fuel injector issues causing lean condition

Symptoms

  • Check Engine Light (MIL) on
  • Stored P1157 (or related O2 sensor/lean bank codes)
  • Poor fuel economy
  • Rough idle or hesitation under load (if lean persists)
  • Elevated long‑term/short‑term fuel trims on Bank 2 when scanned

What to check

  • Scan for current and pending codes and freeze‑frame data
  • Monitor live data: Bank 2 Sensor 2 O2 voltage and switching behavior
  • Check short‑term and long‑term fuel trims for Bank 2 (positive trims suggest lean)
  • Inspect sensor connector and wiring for damage, corrosion, or open circuits
  • Check for exhaust leaks upstream of the downstream sensor (visual/smoke test)
  • Verify fuel pressure and fuel system integrity

Signal parameters

  • Expected downstream O2 (switch‑style) voltage range: approximately 0.1 V (lean) to 0.9 V (rich); threshold ~0.45 V
  • During normal operation the downstream sensor should show occasional switching around the threshold (may be slower than upstream sensors)
  • Heater circuit: supply voltage ~12 V when powered; heater resistance varies by design—compare to vehicle spec (typically single‑digit to a few tens of ohms)
  • If the sensor output is stuck low (~0.1–0.2 V) it indicates a lean reading or no switching

Diagnostic algorithm

  1. Retrieve and record trouble codes and freeze‑frame data; verify P1157 is current. Clear codes and perform a road or drive‑cycle reproduce test while monitoring live data.
  2. Observe Bank 2 Sensor 2 voltage: note whether it switches between lean (~0.1 V) and rich (~0.9 V). If stuck lean, continue diagnostics.
  3. Inspect sensor connector and wiring for corrosion, open, short to ground or power, and pin damage; wiggle harness while monitoring signal for intermittent behavior.
  4. Check heater circuit: with key on engine off, verify heater supply and ground; measure heater resistance and compare to spec. Repair wiring or replace sensor if heater failure or open/short present.
  5. Check for exhaust leaks upstream of the downstream sensor (smoke test or visual inspection). Repair any leaks and retest.
  6. Verify fuel pressure and inspect fuel delivery components (pump, filter, regulator, injectors). Correct any low pressure or injector faults.
  7. Check for intake vacuum leaks and proper MAF/MAP operation; repair as needed.
  8. If wiring and vehicle systems are good, swap a known‑good downstream sensor (or swap sensors between banks if identical) to see if code follows the sensor. Replace sensor if the fault follows it.
  9. After repairs clear codes and perform full drive cycle to confirm the fault is resolved. If persistent, consider catalytic converter evaluation and PCM testing as last steps.

Likely causes

  • Failing post‑cat O2 sensor (Bank 2 Sensor 2)
  • Damaged wiring or corrosion at the sensor connector
  • Exhaust leak near Bank 2 sensor allowing extra oxygen
  • High short‑term/long‑term fuel trim (actual lean) due to fuel delivery or air metering fault

Fault status

⚠️ Status
Downstream heated O2 sensor (Bank 2, Sensor 2) is not switching and indicates a lean condition; needs wiring/sensor and upstream system checks.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-2 hours

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166

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