Code
P1031
SATURN
P — Powertrain
HO2S Heater Current Monitor Control Circuit Sensors 1
AI status
Completed
Completed
100%
Causes
- Open or short in HO2S heater wiring or connector (Bank 1 Sensor 1)
- Blown fuse or faulty heater supply/relay (if equipped)
- Faulty heated oxygen sensor (heater element failed)
- Poor or corroded connector/ground
- Short to voltage or ground in the heater circuit
- Faulty PCM/ECM (rare, after other causes eliminated)
Symptoms
- Check Engine Light (MIL) illuminated
- Failed EVAP/OBD readiness or emissions test
- Longer engine warm-up and increased cold emissions
- Possible rough idle or drivability issues until sensor warms
What to check
- Scan for additional codes and view freeze frame / live data
- Verify presence of code after clearing and a short drive cycle
- Inspect sensor and wiring harness for damage, corrosion, or disconnection
- Check related fuses and relays for the heater circuit
- Measure heater element resistance at sensor connector with connector unplugged
- Backprobe connector with key ON to check supply voltage and switching/ground
Signal parameters
- Heater resistance (typical upstream HO2S): approximately 2–14 ohms (varies by sensor). An open or very high resistance indicates a failed heater.
- Supply voltage: ~12 V from fused circuit with key ON (or battery voltage present at heater supply pin).
- Controlled side: PCM usually switches ground or switches power — expect switching behaviour (grounding) when engine running.
- Heater current: typically under a few amperes; abnormal low/no current or short/high current will set monitor.
Diagnostic algorithm
- Read all codes and freeze frame, note related O2 or heater codes. Clear codes and attempt to re-create the fault.
- Visually inspect Bank 1 Sensor 1 harness and connector for heat damage, corrosion, exposed wires, or rodent damage.
- Check fuses and any heater/ECM relays that supply the sensor heater circuit; replace if blown/faulty.
- Unplug sensor and measure heater resistance across heater pins. If open or outside expected range, replace sensor.
- With connector connected, backprobe heater supply pin with key ON to verify ~12 V (or battery voltage) at supply.
- Backprobe the other heater control pin and crank or run engine; verify PCM is switching ground (or switching voltage) to control heater. Use a lab scope or DVOM to observe switching.
- Check continuity from sensor connector to PCM pins and check for shorts to ground or battery positive. Repair damaged wiring or connectors.
- If wiring and sensor test good but code returns, verify PCM driver output with appropriate tools; consider PCM replacement only after all wiring/sensor checks pass.
- After repairs, clear codes and perform drive cycle to confirm the monitor stays ready and code does not return.
Likely causes
- Damaged sensor heater element (open circuit)
- Corroded or disconnected sensor connector
- Blown fuse feeding the sensor heater
- Wire chafing causing short to chassis ground or battery +
- PCM driver fault (if wiring and sensor test good)
Fault status
Status
HO2S Heater Current Monitor Control Circuit (Bank 1 Sensor 1) — ECM detected abnormal heater circuit current (open, short, low or excessive current).
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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