Code
P1137
JAGUAR
P — Powertrain
Lack Of HO2S12 Switches Sensor Indicates Lean
Views:
UK: 24
EN: 54
RU: 43
AI status
Completed
Completed
100%
Causes
- Actual engine lean condition (vacuum/exhaust leak, low fuel pressure, clogged injector)
- Faulty HO2S (Bank 1 Sensor 2) — slow, contaminated or failed sensor
- Wiring problems: open, short to ground, corrosion or poor connector
- Heater circuit fault in the downstream O2 sensor
- Exhaust leak upstream of the downstream sensor (between bank 1 and sensor)
- Faulty Mass Air Flow (MAF) or MAP sensor or intake leak causing incorrect fueling
Symptoms
- Check Engine Light (MIL) illuminated
- Poor fuel economy
- Rough idle or hesitation under load
- Failed emissions test (high NOx/HC or lean-related fail)
- Possible reduced driveability or surging at steady cruise
What to check
- Read freeze frame and live data: downstream (B1S2) O2 voltage and switching behavior, upstream O2 (B1S1) for comparison, and short/long-term fuel trims (STFT/LTFT)
- Visual inspection of the sensor wiring and connector for damage, corrosion, or poor connection
- Inspect exhaust for leaks upstream of the downstream sensor (manifold, gasket, collector)
- Check fuel pressure and fuel delivery (fuel pump, filter, injectors)
- Perform smoke test or prop test for intake/vacuum leaks
- Verify MAF/MAP sensor readings and intake air leaks
Signal parameters
- Typical zirconia O2 sensor voltage: ~0.0–1.0 V (lean low ~0.6–0.7 V)
- Upstream sensor (B1S1) should switch frequently at idle; downstream (B1S2) typically shows lower amplitude or slower changes if catalyst working
- Persistent low/low-amplitude B1S2 voltage or failure to switch toward rich indicates lean bias
- Heater circuit: low resistance (spec varies by sensor) and proper operation at key-on/run — heater should warm sensor quickly
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note fuel trims, B1S1 and B1S2 voltages and behavior.
- Monitor live data: observe B1S1 vs B1S2 during key-on and engine running (idle, snap throttle). Confirm that B1S2 is biased low or not switching.
- Inspect O2 sensor connector and wiring for damage, corrosion, or chafing. Wiggle test while monitoring live data for intermittent changes.
- Check for exhaust leaks upstream of B1S2 (visual, smoke test, or listen for blowing). Repair any leaks and retest.
- Check fuel pressure and volume against manufacturer spec; inspect fuel filter and fuel pump operation. Repair as needed.
- Test for intake vacuum leaks (smoke test) and verify MAF/MAP sensor readings. Repair or replace faulty components and retest.
- Test O2 sensor heater circuit resistance and supply/ground at the connector; verify heater current at key-on/run. Replace sensor if heater or resistance out of spec.
- If wiring and fuel delivery are good, consider replacing downstream HO2S (B1S2) and re-run tests before replacing other parts.
- After repairs clear codes and road test while monitoring O2 sensors and fuel trims to confirm the code does not return.
Likely causes
- Exhaust leak between head/collector and sensor (introducing extra oxygen)
- Contaminated or failed downstream O2 sensor (slow to respond or stuck low)
- Low fuel pressure or restricted fuel delivery causing lean running
- Wiring/connector damage or poor ground at sensor circuit
- Intake vacuum leak or faulty MAF/MAP causing lean fuel trim
Fault status
Status
HO2S Bank 1 Sensor 2 indicates lean condition — PCM detected low/biased downstream oxygen sensor signal. Could be lean fuel condition, sensor failure, wiring or heater issue, or exhaust/intake leak.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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