P2221: NOx Sensor Heater Sense Circuit Bank 2
What to do
The car drives normally and this is the milder of the heater faults. Still worth repairing — an unregulated heater is harder on an expensive sensor over time — and connector corrosion, the usual cause, is cheap to correct.
What this code means
A fault in the circuit through which the module monitors the bank 2 heater, as distinct from the one through which it drives it. The control-versus-sense distinction, and why the heater's own resistance serves as a thermometer that turns heating into a closed loop, is set out at P2208.
This is graded below the control faults for the reason given there: the heater may well still be working, but the module can no longer verify or regulate it precisely.
Likely causes
Start here
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
Less common
- Faulty NOx sensor · moderate
- Water ingress into connector · easy
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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