P2218NOx Sensor Heater Control Circuit/Open (Bank 2)
The control circuit for the Bank 2 NOx sensor heater has an open or general fault, so the sensor cannot reach operating temperature.
Definition
The Bank 2 NOx sensor's ceramic element must be heated to roughly 800°C before it produces valid readings, and the control module monitors the heater control circuit for opens and implausible states. P2218 sets when that circuit is open or fails its rationality check, leaving the sensor cold and its NOx data invalid. The MIL illuminates, the NOx and SCR readiness monitors cannot complete, and diesel applications risk degraded DEF dosing and eventual inducement derate if the fault persists.
Common causes
- Failed heater element inside the Bank 2 NOx sensor
- Open heater control wiring or broken terminal
- Corroded connector between sensor module and harness
- Blown fuse or failed relay on the sensor heater supply
- Control module heater driver fault (rare)
Common misdiagnoses
- SCR catalyst or DPF
- DEF dosing valve
- Bank 1 sensor replaced instead of Bank 2
- Oxygen sensor heater
Troubleshooting steps
1.Check fuses and heater supply voltage
Verify the fuse feeding the Bank 2 sensor module is good and battery voltage is present at the sensor connector, key on.
2.Measure heater resistance if specified
Compare the heater element reading against the published spec (commonly single-digit ohms cold); an open circuit condemns the sensor.
3.Inspect harness and connectors
Look for broken wires at flex points and backed-out terminals at the sensor module connector.
4.Monitor heater operation on a scan tool
Watch heater duty, current, or sensor temperature PIDs after dew-point release; no heater activity with verified wiring means the sensor has failed.
5.Replace the sensor and verify readiness
After installing an OE sensor, clear codes and confirm valid NOx readings and monitor completion on a road test.