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Home / DTC / P0038 — Oxygen sensor heater(rear) high

P0038 — Oxygen sensor heater(rear) high

Detailed page for trouble code P0038.

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Code

P0038

MITSUBISHI P — Powertrain

Oxygen sensor heater(rear) high

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

Causes

  • Short to battery voltage on the heater feed or control wire
  • Open, corroded or damaged connector or wiring (intermittent/high resistance)
  • Failed heater element in the oxygen sensor (internal short)
  • Poor or missing ground for the heater circuit
  • Faulty ECM / heater driver transistor
  • Incorrect replacement sensor or aftermarket harness wiring error

Symptoms

  • MIL (Check Engine Light) illuminated
  • Possible failed emissions readiness for O2 sensor heater monitor
  • Possible increased tailpipe emissions
  • Usually no major drivability issues (engine may run normally)
  • Heater-related codes may prevent proper catalytic converter testing during emissions inspection

What to check

  • Retrieve freeze-frame and live data with a scan tool; confirm P0038 and note any related codes
  • Visually inspect sensor connector and wiring for corrosion, damage, pinch points, repairs, or water intrusion
  • Backprobe the heater connector and observe voltage with key ON (engine OFF) and with engine running
  • Check for battery voltage on the heater feed circuit and verify the ECM control side behavior (should be switched to ground by ECM)
  • Measure heater element resistance at sensor (compare to factory spec)
  • Check for continuity to ground and for shorts to battery feed using a multimeter

Signal parameters

  • Heater feed: battery voltage present with key ON (approx. vehicle battery voltage)
  • ECM control: switches/heats by grounding the heater circuit (control terminal may be pulsed)
  • Fault condition: control terminal voltage remains high (near battery) when ECM expects to pull to ground
  • Heater element resistance: compare to factory spec (typical direction: low ohms; many sensors are roughly single-digit ohms to a few tens of ohms)
  • No-circuit condition: infinite resistance (open) — short condition: resistance much lower than spec or direct short to battery

Diagnostic algorithm

  1. Connect a scan tool, record codes and freeze-frame data; clear codes and confirm P0038 returns
  2. Visually inspect the downstream O2 sensor (rear) connector and wiring for damage, corrosion, water entry, or repairs
  3. With key ON (engine OFF), backprobe the sensor heater connector: verify battery voltage at the feed pin and observe the control pin for proper switching/pulsing when ECU runs the heater test
  4. Measure heater element resistance at the sensor itself (unplug sensor) and compare to the factory specification; if out of spec, replace sensor
  5. Check continuity from the sensor heater control wire to the ECM connector and check for shorts to battery or to ground; repair any damaged wiring or connectors
  6. If wiring and sensor resistance are good but the control wire remains high, substitute a known-good downstream sensor (if available) or temporarily disconnect/reconnect to retest behavior
  7. If the heater circuit still reads high after sensor and wiring verified good, suspect ECM heater-driver failure — confirm with manufacturer diagnostic flow; replace ECM only after all other causes eliminated
  8. After repairs, clear codes, perform readiness/drive cycle and confirm code does not return

Likely causes

  • Shorted heater feed to battery or constant 12 V (most likely)
  • Failed oxygen sensor heater element
  • Damaged/wet/corroded connector or wiring harness near the sensor
  • ECM heater-driver fault (least likely)

Fault status

⚠️ Status
Oxygen sensor heater (rear) control circuit voltage high — possible short to battery, wiring/connector fault, sensor heater failure, or ECM driver fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0037 P0058 P0030 P0138 P0057
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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