HO2S Heater Resistance (Bank 1, Sensor 2)
The downstream oxygen sensor (Bank 1, Sensor 2) heater circuit is not functioning properly. The heater element warms the O2 sensor quickly after cold start so it can provide accurate readings to the engine computer.
What You Might Notice
- Delayed engine startup or hard cold starts
- Diminished fuel efficiency
- Black smoke or excessive smoke from exhaust
- Rich fuel mixture at startup
- Check Engine light illuminated
Most Common Causes
- 1
Faulty oxygen sensor heater element
The internal heating element inside the downstream O2 sensor has failed or lost electrical continuity, preventing the sensor from reaching operating temperature.
- 2
Broken heater circuit wiring or connectors
Corroded, damaged, or loose wiring and connectors in the O2 sensor heater circuit can prevent power from reaching the heater element.
- 3
Failed heater relay or control module
The engine control module or heater control relay may be unable to supply the correct voltage or ground to the heater circuit.
- 4
High resistance in heater circuit
Excessive resistance due to corrosion, poor connections, or damaged wiring prevents adequate current flow to the heater element.
How to Diagnose It
- 1
Check Faulty oxygen sensor heater element — The internal heating element inside the downstream O2 sensor has failed or lost electrical continuity, preventing the sensor from reaching operating temperature.
- 2
Check Broken heater circuit wiring or connectors — Corroded, damaged, or loose wiring and connectors in the O2 sensor heater circuit can prevent power from reaching the heater element.
- 3
Check Failed heater relay or control module — The engine control module or heater control relay may be unable to supply the correct voltage or ground to the heater circuit.
- 4
Check High resistance in heater circuit — Excessive resistance due to corrosion, poor connections, or damaged wiring prevents adequate current flow to the heater element.
How to Fix It
- 1
Replace downstream oxygen sensor
Remove and replace the Bank 1 Sensor 2 oxygen sensor with a new unit. Ensure proper installation and torque specifications are met.
- 2
Inspect and repair heater circuit wiring
Trace the O2 sensor heater wiring from the connector to the sensor, checking for corrosion, cuts, and loose connections. Repair or replace damaged sections and clean corroded connectors.
- 3
Test and replace heater control relay
Use a multimeter to test the heater relay for proper operation. If defective, replace the relay according to vehicle specifications.
- 4
Perform system diagnostic and retest
Clear the fault code using a diagnostic scanner, perform a complete system test including voltage and resistance measurements at the O2 sensor connector, and verify the code does not return after startup and driving cycles.
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