Code
P1031
OLDSMOBILE
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
- Corroded, damaged, or loose sensor connector pins
- Failed HO2S heater element (internal open or high resistance)
- Blown fuse or failed relay supplying the heater circuit
- Poor ground or battery/charging system voltage problems
- Faulty PCM or heater-driver transistor (less common)
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Reduced cold-start emissions control and possible failed emissions test
- Poor fuel economy or driveability issues during warmup
- Longer warm-up time for closed-loop operation; may affect idle or acceleration when cold
What to check
- Verify stored DTC(s) and freeze frame data with a scan tool
- Visual inspection of sensor, wiring, and connector for damage, corrosion, or melting
- Check related fuses and relays for the heater circuit
- Measure battery voltage and charging system health
- Confirm presence of other O2-sensor related codes (helps narrow cause)
Signal parameters
- Heater supply voltage: typically battery voltage (~12 V) when PCM commands heater ON (varies by vehicle)
- Heater resistance (cold): generally low — commonly a few ohms to a few tens of ohms (manufacturer spec required)
- Heater current draw when energized: typically under 3–4 A for a single sensor heater (varies by design)
- PCM monitors heater current/feedback and flags fault if current is open, short, or outside expected range
Diagnostic algorithm
- Connect a scan tool, read and record freeze frame and all stored/ pending codes. Confirm P1031 is current and note drive conditions when set.
- Visually inspect the Bank 1 Sensor 1 connector, wiring harness, and underhood routing for damage, chafing, corrosion, heat damage, or loose terminals.
- Check related fuses/relays for the heater circuit and replace if blown; verify fuse circuit has good continuity to the harness.
- With ignition OFF, disconnect the sensor and measure heater resistance across the heater pins. Compare to manufacturer spec — an open or very high resistance indicates a bad heater element.
- With a DVOM, check for continuity between the sensor heater circuit and the PCM connector. Repair any open circuits or high-resistance connections.
- Backprobe the heater supply terminal with engine OFF and with ignition ON (and with heater commanded ON via scan tool if available). Verify supply voltage is present and the PCM is commanding the heater (or ground switching), and measure current draw if possible.
- If heater supply and grounds are correct but resistance was within spec, swap the sensor with a known-good unit or apply a fused 12 V feed briefly to see if the heater element draws current (use appropriate fuse and caution).
- If wiring and sensor check OK, test or substitute the PCM/driver circuit only after verifying all wiring and connectors — PCM faults are less common.
- After repair or replacement, clear codes, perform a drive cycle or monitor readiness until the PCM confirms the circuit is normal.
- Safety note: take care when backprobing live circuits; use insulated tools and proper fusing when applying power to components.
Likely causes
- Wiring open/corroded connector between sensor and PCM
- Failed heater element in the oxygen sensor
- Blown fuse or weak/poor ground connection
Fault status
Status
PCM detected abnormal heater current or control circuit condition for HO2S Sensor 1 (heater open/short/high resistance). Fault logged and MIL may be on. Requires wiring, sensor, fuse/relay, or PCM driver investigation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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