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Home / DTC / P0158 — Oxygen sensor2(rear) high

P0158 — Oxygen sensor2(rear) high

Detailed page for trouble code P0158.

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Code

P0158

MITSUBISHI P — Powertrain

Oxygen sensor2(rear) high

Brand: MITSUBISHI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty or contaminated downstream O2 sensor (Bank 2, Sensor 2)
  • Wiring shorted to battery voltage (12V) in the sensor harness or connector
  • Poor or intermittent ground for the sensor circuit
  • Rich exhaust condition (excess fuel delivery)
  • Faulty fuel pressure regulator or leaking fuel injector(s)
  • Faulty upstream sensor or catalytic converter affecting downstream readings

Symptoms

  • Check Engine Light (MIL) on
  • Reduced fuel economy if vehicle is running rich
  • Possible rough idle or hesitation (if the condition also affects fuel trims)
  • Failed emissions test
  • Usually no obvious exhaust smell unless rich condition is severe

What to check

  • Read freeze frame and live data for Bank 2 Sensor 2 voltage and compare to Bank 2 Sensor 1 (upstream)
  • Visual inspection of sensor wiring and connector for damage, corrosion or melted insulation
  • Backprobe sensor connector while engine is running to observe voltage behavior
  • Measure sensor heater resistance and check for proper supply voltage and ground
  • Check short to 12V on the sensor signal wire with ignition on (engine off)
  • Scan fuel trims, fuel pressure and look for other DTCs (misfires, fuel system codes, MAF, coolant temp)

Signal parameters

  • Downstream O2 sensor (Bank 2, Sensor 2) normal steady voltage: typically ~0.1–0.6 V (does not switch rapidly like upstream)
  • High-voltage fault threshold: sensor voltage above ~0.8–0.9 V for a set time (manufacturer-dependent)
  • Heater resistance (typical range): approx. 5–30 ohms (verify with service data for exact spec)
  • Supply voltage to heater circuit: battery voltage (~12 V) when relay/fuse active; control by ECM for some designs

Diagnostic algorithm

  1. Connect a scan tool and record freeze-frame, monitor B2S2 voltage and B2S1 simultaneously while engine is at operating temperature.
  2. Visually inspect B2S2 connector and wiring harness for corrosion, broken wires, chafing or overheating. Repair any obvious damage.
  3. With ignition ON (engine OFF) check the signal wire for a short to 12V using a multimeter—measure voltage at the harness connector; if steady ~12V, suspect short or terminal contact.
  4. With engine running and safe to do so, backprobe the sensor signal and observe voltage. Downstream should be relatively steady; if it reads high (~0.9 V) while upstream reads normal (~0.1–0.9 switching) then suspect sensor or local wiring.
  5. Check heater circuit: measure resistance of heater element against spec and verify power/ground at harness with ignition ON. Replace sensor if heater open or not powered correctly.
  6. If wiring and heater check OK, compare fuel trims and fuel pressure. Look for signs of a rich condition (high fuel pressure, leaking injector, stuck open purge valve). Repair fuel system faults and re-test.
  7. If wiring and engine conditions are normal but B2S2 still reports high, replace the downstream O2 sensor and clear codes; verify repair by checking live data and completing required drive cycles.
  8. If code returns after sensor replacement, perform ECM and wiring harness continuity checks and consider ECM evaluation.

Likely causes

  • Sensor element stuck high due to contamination (oil, coolant, silicone, sulfur)
  • Connector pin corrosion or terminal pushed out allowing a short to 12V
  • Damaged insulation allowing chafing to a power feed
  • Excessive fuel pressure or leaking injector causing consistently rich exhaust
  • Wiring open in ground return or high resistance ground connection

Fault status

⚠️ Status
P0158 — Oxygen sensor 2 (rear) high voltage on Bank 2. ECM detected a higher-than-expected downstream O2 sensor signal, indicating either a rich exhaust reading or an electrical fault in the sensor circuit.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-2 hours
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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