Code
P1133
GWM
P — Powertrain
- Sensor 1 HO2S
AI status
Completed
Completed
100%
Causes
- Open or short in HO2S heater circuit (wiring, connector, or sensor)
- Failed heated oxygen sensor (internal heater element open or degraded)
- Blown fuse or faulty relay supplying heater circuit
- Poor ground or corroded connector contacts
- Intermittent wiring damage (chafing, broken strands)
- Exhaust leak near the sensor affecting readings
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Poor cold-start driveability or longer open-loop operation
- Reduced fuel economy and increased emissions
- Rough idle until engine reaches operating temperature
- Possible failed emissions test
What to check
- Read and record stored/active codes and freeze-frame data with a scan tool
- Visually inspect sensor, connector, and wiring for damage, corrosion, or heat damage
- Check relevant fuses and relays for the heater circuit
- Back-probe sensor connector to confirm heater supply voltage and ground
- Measure heater resistance at the sensor (engine cold) with multimeter
- Command heater ON via scan tool (if supported) and confirm current/voltage
Signal parameters
- Typical HO2S heater resistance (cold): ~2–20 ohms (manufacturer-specific; consult manual)
- Heater supply voltage: battery voltage (~12 V) or switched voltage when commanded
- Oxygen sensor output voltage (sensor signal): 0.0–1.0 V switching in closed-loop
- Heater current draw: varies by sensor (often 0.5–3 A); compare to spec
Diagnostic algorithm
- Verify MIL and retrieve all related codes; note freeze-frame and readiness status.
- Perform a visual inspection of Bank 1 Sensor 1 wiring, connector, and sensor for contamination, heat damage, or corrosion.
- Check and verify fuses/relays powering the HO2S heater circuit; replace if blown.
- With ignition OFF, disconnect sensor and measure heater element resistance across heater pins; compare to spec. An open or very high resistance indicates bad sensor.
- With ignition ON (engine off) or engine running as appropriate, back-probe connector to check heater supply voltage and ground. Use a scan tool to command heater ON (if available) and observe voltage/current response.
- Wiggle harness and connectors while monitoring heater circuit and live O2 data to find intermittent shorts/open circuits.
- If wiring, connector, or fuse is faulty: repair or replace wiring/connector, clean contacts, and secure harness away from heat sources.
- If heater element is open or out of spec and wiring is good: replace the upstream HO2S (Bank 1 Sensor 1).
- After repairs, clear codes, perform a drive cycle or readiness verification, and confirm code does not return.
- If fault persists after replacing sensor and repairing wiring, consider ECM/PCM driver fault and consult manufacturer procedures for module testing/repair.
Likely causes
- Damaged sensor connector (water intrusion, corrosion)
- Open or high-resistance heater element inside sensor
- Blown heater fuse or bad relay
- Wiring short to battery or ground at harness near exhaust
- Failed ECM driver (less common)
Fault status
Status
Heated oxygen sensor (Bank 1, Sensor 1) heater circuit fault — open, short, high resistance, or intermittent. Check sensor, wiring, power/ground, and related fuses/relays.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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