NOx Sensor Heater Control Circuit Low Bank 1
The NOx sensor heater control circuit on Bank 1 is detecting a low voltage condition, meaning the heater element isn't receiving adequate power. This prevents the nitrogen oxide sensor from reaching proper operating temperature, causing inaccurate emissions readings and potential emissions test failures.
What You Might Notice
- Check Engine Light (CEL) illuminated
- Failed emissions test
- Intermittent CEL that comes and goes
- Rough idle or hesitation under acceleration
- Reduced fuel economy
Most Common Causes
- 1
Faulty NOx sensor heater element
The heater element inside the NOx sensor has failed or is shorting to ground, causing insufficient resistance and low circuit voltage.
- 2
Wiring harness damage or corrosion
The heater control circuit wiring is corroded, damaged, or has poor connections that prevent adequate current flow to the heater.
- 3
Failed NOx sensor heater relay or module
The relay or control module that energizes the heater circuit has malfunctioned or lost connection, cutting power to the sensor heater.
- 4
Faulty Engine Control Module (ECM)
The ECM's heater control output has failed, preventing it from properly commanding the heater circuit even if the wiring and sensor are functional.
How to Diagnose It
- 1
Check Faulty NOx sensor heater element — The heater element inside the NOx sensor has failed or is shorting to ground, causing insufficient resistance and low circuit voltage.
- 2
Check Wiring harness damage or corrosion — The heater control circuit wiring is corroded, damaged, or has poor connections that prevent adequate current flow to the heater.
- 3
Check Failed NOx sensor heater relay or module — The relay or control module that energizes the heater circuit has malfunctioned or lost connection, cutting power to the sensor heater.
- 4
Check Faulty Engine Control Module (ECM) — The ECM's heater control output has failed, preventing it from properly commanding the heater circuit even if the wiring and sensor are functional.
How to Fix It
- 1
Inspect and replace NOx sensor
Remove the NOx sensor on Bank 1 and inspect the heater element for damage or corrosion. Replace the sensor if the heater is faulty. Verify proper installation and electrical connection.
- 2
Check and repair wiring harness
Inspect the NOx sensor heater control circuit wiring for corrosion, breaks, or loose connections. Clean corroded connectors with dielectric grease and reseat all connections. Repair or replace damaged wiring as needed.
- 3
Test and replace heater relay or control module
Use a multimeter to test the heater relay or control module for proper operation. If voltage is not reaching the sensor heater during engine operation, replace the faulty relay or module.
- 4
Diagnose and reprogram ECM if necessary
If all other components test good, the ECM may have a failed output driver or need reprogramming. Have the ECM scanned for internal faults and reflashed or replaced if defective.
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