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Home / DTC / P0031 — Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 1

P0031 — Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 1

Detailed page for trouble code P0031.

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Code

P0031

HUMMER P — Powertrain

Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 1

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
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Page language: EN

Causes

  • Blown fuse or faulty relay supplying the O2 heater circuit
  • Open, corroded or loose connector at the sensor or inline connector
  • Damaged wiring (open, high resistance) between fuse/relay and sensor
  • Poor ground or grounding point corrosion for the heater circuit
  • Failed oxygen sensor heater element
  • PCM (engine control module) fault or internal driver failure

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Delayed catalytic/oxygen sensor warm-up and reduced closed-loop operation
  • Higher emissions and possible failed emissions test
  • Rough or rich/lean running until sensor warms up
  • Reduced fuel economy or drivability issues during cold start

What to check

  • Read freeze frame and live data with a scan tool; confirm P0031 and any related codes
  • Visual inspection of sensor, connector, wiring harness and chassis grounds for damage, corrosion, or contamination
  • Check relevant fuses and relays for continuity and proper operation
  • Backprobe the sensor heater connector with key ON (engine off) to confirm supply voltage and to the control side to check switching to ground
  • Measure heater element resistance with sensor disconnected using a DMM
  • Perform voltage drop and continuity checks between fuse/relay, PCM, and sensor harness

Signal parameters

  • Expected supply voltage to heater fuse/relay: approximately battery voltage (~11–14 V) with key ON/engine running
  • Expected heater element resistance (typical range): ~2–20 ohms (varies by sensor design)
  • Expected heater current draw when powered: roughly 0.5–2 A (dependent on resistance)
  • Heater should bring sensor to operating temperature within a few seconds to tens of seconds under normal conditions (manufacturer-specific)

Diagnostic algorithm

  1. Retrieve codes and freeze frame with a scan tool; record engine conditions when DTC set and note related codes (other O2/engine codes).
  2. Visually inspect Bank 1 Sensor 1 connector and wiring for corrosion, breaks, pin push-out, or overheating. Repair obvious damage before further testing.
  3. Check fuses and relays that feed the O2 heater circuit; replace if blown/faulty and retest.
  4. With the sensor disconnected, measure resistance across the heater terminals with a DMM. Compare to typical range (2–20 Ω). Very high/infinite resistance indicates an open heater. Very low/short indicates shorted element.
  5. With ignition ON (engine OFF), backprobe the power supply terminal at the sensor connector and verify battery voltage is present at the supply lead. If no voltage, trace to fuse/relay/wiring.
  6. Command the heater ON via bi-directional control (if scan tool supports) and measure voltage/current at the sensor connector and verify PCM switching to ground on the control side. Observe for low voltage or lack of switching.
  7. Perform continuity/voltage-drop checks between sensor connector and PCM power/ground points to identify high-resistance joints. Repair poor connections.
  8. If wiring and supply/ground are good but heater resistance or operation is out of spec, replace the O2 sensor. Clear codes and re-test road/drive cycle.
  9. If a new sensor still sets the code and wiring/grounds check good, evaluate PCM heater driver operation and consider module diagnostics/repair per vehicle service manual.

Likely causes

  • Blown fuse or relay feeding the heater
  • Broken/shorted wiring or high-resistance connector at Bank 1 Sensor 1
  • Failed heater element inside the O2 sensor
  • Bad ground at the sensor or chassis ground wire
  • PCM heater driver malfunction

Fault status

⚠️ Status
Stored when the PCM detects lower-than-expected voltage or inadequate heater operation on the HO2S heater circuit for Bank 1 Sensor 1; typically triggers MIL and requires inspection of heater power, ground, wiring, and the sensor.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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P0030 P0032 P0135 P0155 P0050
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