Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / P0161 — Oxygen sensor2(rear) heater

P0161 — Oxygen sensor2(rear) heater

Detailed page for trouble code P0161.

34,771codes
59brands
11,925generic
22,846specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

P0161

MITSUBISHI P — Powertrain

Oxygen sensor2(rear) heater

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

Causes

  • Open or short in the oxygen sensor heater wiring
  • Blown fuse or faulty relay for heater circuit
  • Corroded, loose, or water‑intruded sensor connector
  • Failed oxygen sensor heater element (internal open/high resistance)
  • Faulty engine control module (ECM) driver for the heater
  • Incorrect or damaged replacement sensor

Symptoms

  • MIL/Check Engine light illuminated
  • Possible poor cold‑start emissions and failed emissions test
  • Longer sensor warmup leading to delayed closed‑loop operation
  • Occasional rough idle or reduced fuel economy (indirect)
  • No immediate drivability symptoms in some cases

What to check

  • Read and record freeze‑frame data and stored DTCs with a scan tool
  • Visually inspect sensor, connector, and wiring for damage, corrosion, or water intrusion
  • Check appropriate fuse(s) and relays for the heater circuit
  • Measure heater element resistance at the sensor (compare to spec)
  • Backprobe connector with key ON/engine running to check for control voltage or switching to ground
  • Perform wiggle test while monitoring heater control signal and DTCs

Signal parameters

  • Typical heater resistance: low ohms (commonly ~3–20 Ω; consult model spec)
  • Heater supply voltage: near battery voltage when the circuit is powered (~11–14 V)
  • Control signal: ECU switches supply or ground (pulsed) to regulate current — may be PWM
  • Current draw when heater active: usually
  • Note: exact values vary by model year; always compare to manufacturer specifications

Diagnostic algorithm

  1. Confirm P0161 and any related DTCs with a scan tool; record freeze frame and readiness status
  2. Visually inspect downstream O2 sensor, connector, and wiring for obvious damage, corrosion, or water entry
  3. Check fuses and relays for the heater circuit; replace if blown and retest
  4. Unplug sensor and measure heater element resistance across the heater terminals; if open or out of spec, replace the sensor
  5. With connector disconnected, check for battery voltage or switched power at the heater feed terminal (key ON/engine OFF) and for control switching at the other terminal with the engine running (backprobe safely)
  6. If no power or switching present, trace wiring for open/short to power/ground and repair as needed
  7. If wiring and power are good but heater open or abnormal, install a known good sensor and retest
  8. After repairs, clear codes, complete readiness cycle or drive test, and confirm code does not return
  9. If wiring and sensor check good but no control from ECM, consider ECM driver fault and pursue ECM testing/repair per manufacturer procedures

Likely causes

  • Open or shorted heater element in the downstream O2 sensor
  • Damaged wiring harness or chafed insulation near sensor plug
  • Corroded/contaminated connector preventing current flow
  • Blown fuse or failed relay supplying the heater circuit
  • ECM output driver failure (less common)

Fault status

⚠️ Status
PCM reports malfunction in the rear oxygen sensor (sensor 2) heater circuit — heater element open/short/high resistance or control circuit fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0135 P0141 P0155 P0156 P0157 P0158
406

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

MITSUBISHI

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .