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Home / DTC / P0135 — Oxygen sensor(front) heater

P0135 — Oxygen sensor(front) heater

Detailed page for trouble code P0135.

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Code

P0135

MITSUBISHI P — Powertrain

Oxygen sensor(front) heater

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

Causes

  • Blown fuse or defective relay for O2 heater circuit
  • Open or shorted wiring between sensor and ECM
  • Corroded, loose or damaged sensor connector
  • Failed/heater element in the oxygen sensor
  • High circuit resistance due to corrosion or damaged pins
  • Faulty ECM or driver transistor (rare)

Symptoms

  • Malfunction Indicator Lamp (MIL/Check Engine) illuminated
  • Longer warm-up time for closed-loop operation and richer running until sensor warms
  • Reduced fuel economy and increased emissions
  • Failed emissions test (HC/CO elevated)
  • Occasional rough idle or hesitation while sensor fails to reach operating temperature

What to check

  • Read and record freeze frame and freeze data with a scan tool
  • Visually inspect oxygen sensor wiring, connector, and nearby harness for damage, corrosion, or heat damage
  • Check relevant fuses and relays for the heater circuit
  • Back-probe sensor heater connector with key ON (engine OFF) to verify voltage supply
  • Measure heater resistance at the sensor (with connector disconnected)
  • Check continuity and resistance of wiring between sensor connector and ECM connector/pin

Signal parameters

  • Typical heater resistance: commonly ~3–20 ohms for narrowband heated O2 sensors (compare to OEM spec)
  • Supply voltage to heater: battery voltage (~11–14 V) when heater is commanded ON or on Key ON depending on design
  • Heater current draw: typically up to ~0.5–2.0 A depending on sensor design
  • ECM monitors heater circuit for open/short/high resistance conditions and will set P0135 if abnormal

Diagnostic algorithm

  1. Read DTCs and related codes; note freeze frame data and freeze parameters.
  2. Confirm vehicle-specific details in factory service manual (pinouts, connector locations, resistance spec).
  3. Perform a visual inspection of Bank 1 Sensor 1 wiring and connector; repair obvious damage.
  4. With key ON (engine OFF) back-probe the heater power terminal at the sensor connector and verify battery voltage or switched power is present; check applicable fuse/relay if no power.
  5. Disconnect sensor; measure heater resistance across heater pins at the sensor. Compare to OEM spec — open or very high resistance indicates failed heater and sensor replacement.
  6. If resistance is within spec, check continuity and resistance between sensor connector and ECM heater control pin. Repair any opens or high resistance.
  7. If power and continuity are good but ECM does not drive heater, check for short to ground or short to power in the driver circuit and test ECM driver output with scope or shop diagnostic tool per service manual.
  8. Replace the oxygen sensor only after confirming heater circuit power/ground/wiring are correct. Use OEM or quality equivalent sensors.
  9. Clear codes, perform a road test and monitor O2 heater operation and readiness; confirm code does not return.
  10. If all wiring and sensor check out and code returns, consider ECM/driver failure and consult dealer-level diagnostics.

Likely causes

  • Heater element inside Bank 1 Sensor 1 has failed (open)
  • Connector pins corroded or pushed out at sensor or ECM
  • Power feed (fuse/relay) to heater is blown or intermittent
  • Ground/ECM driver wire open, shorted to ground, or shorted to battery
  • High resistance in wiring from heat damage or rodent chew

Fault status

⚠️ Status
ECM detected a malfunction in the heater control circuit for the front oxygen sensor (Bank 1 Sensor 1). Circuit shows open/short/high resistance or insufficient heater current, preventing the sensor from reaching or maintaining operating temperature.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0030 P0141 P0155 P0136 P0134
406

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