OBD-II trouble code
P2218: NOx Sensor Heater Control Circuit/Open (Bank 2)
The heater circuit for the bank 2 nitrogen oxide sensor reads open. Before condemning it, understand when this heater is allowed to switch on — it is deliberately held off until the exhaust is calculated to be dry, which makes the timing of this code as informative as the code itself.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $10 – $1,400
- DIY difficulty
- Intermediate DIY
Browse every code in P2200–P229F, or start from the full code library.
What does P2218 mean?
The heater on a nitrogen oxide sensor is not a convenience feature that shortens the wait for a reading. It is the only way the sensor works at all: the ceramic element measures nothing useful until it is at operating temperature, several hundred degrees above what the exhaust alone delivers reliably, so the element is brought up and held there electrically.
What makes this code different from an ordinary heater fault is the rule governing when that heating is allowed to begin. A cold exhaust pipe is full of condensed water. Combustion makes water vapour, it condenses on cool metal, and it sits in the system until the pipe is hot enough to drive it off. Bringing a ceramic element rapidly to red heat while liquid water is still landing on it cracks it — the thermal shock is severe and the damage is immediate. So the control unit does not simply switch the heater on at key-on. It waits, running a dew point calculation from exhaust temperature, engine run time and load, and only energises once it concludes the pipe is dry.
That single design decision has three practical consequences for this code, and they are the reason it is worth reading past the title.
The first is timing. The heater cannot report open until it has been commanded, so this code sets partway into a drive rather than at start-up. A vehicle that shows the fault ten or fifteen minutes after a cold start is behaving exactly as designed, and the delay is not evidence of an intermittent problem.
The second belongs specifically to the bank 2 position. Where the second address is used for the sensor further down the exhaust — which on inline engines it usually is — that sensor sits in the coolest part of the system, so its dew point condition is satisfied latest and, on short journeys, sometimes not at all. A vehicle used for ten-minute trips in cold weather can go days without its downstream heater being commanded, which means days without the fault being detectable. An owner reporting that the light comes on only on longer runs is describing normal detection behaviour rather than a second symptom.
The third is about what you are allowed to conclude from a single occurrence. Because the enable condition depends on weather, journey length and how the vehicle is used, a heater code that appears once after an unusual trip and does not return is weak evidence. Verify across a proper drive before replacing an expensive sensor.
As for the fault itself, an open reading has a short list of physical causes and they are worth working in order of cost. The supply side comes first: a blown fuse or a failed relay takes the whole circuit out and costs almost nothing to check. Then the harness, particularly at the points where the bank 2 run passes close to hot components. Then the connector, where a spread or backed-out terminal produces exactly the same open-circuit result as a broken wire and is far more common than a broken wire on a vehicle that has had previous work done. The heater element inside the sensor itself is last on the list by cost, not by likelihood — elements do fail open with age, and once they do the sensor is not serviceable.
Expect this code to travel with company. An element that never reaches temperature cannot produce a usable reading, so a heater fault frequently sets a sensor circuit or performance code alongside it. Fix the heater first: the second code is often a consequence rather than a separate problem, and replacing a sensor for the wrong one of the two is an expensive way to find that out.
The vehicle drives normally. The cost of leaving it is the loss of the emissions monitor and, on diesels, the usual staged inducement in time.
Common causes
- Open heater element inside the bank 2 nitrogen oxide sensor
- Blown fuse or failed relay feeding the heater circuit
- Broken or chafed heater supply or control wire along the bank 2 harness run
- Backed-out, spread or unlatched terminal in the sensor connector
- Corrosion at the connector or at a ground point interrupting the circuit
- Element cracked by thermal shock from water contact, taking the heater with it
- Harness damage where the run passes close to hot exhaust components
- Failed driver inside the sensor control unit or the engine controller
- Connector damaged during previous exhaust or aftertreatment work
- Incorrect replacement sensor whose heater the controller cannot drive properly
Symptoms
- Check engine light appearing partway into a drive rather than at start-up
- Fault that appears on long journeys and stays away on short ones
- Nitrogen oxide reading absent or invalid in live data
- Sensor circuit or performance code stored alongside the heater code
- Emissions readiness monitor that will not complete
- Reductant dosing suspended or operating without feedback
- Reduced power inducement on diesels if left unrepaired
- No change in how the engine runs, sounds or pulls
Diagnostic steps
- 1.Note when in the drive cycle the code sets. A fault that appears ten or fifteen minutes after a cold start is normal detection timing, because the heater is deliberately held off until the exhaust is calculated to be dry.
- 2.Verify the fault across a full drive rather than acting on a single occurrence, especially on a vehicle used for short journeys in cold weather where the heater may rarely be commanded at all.
- 3.Check the fuse and relay feeding the heater circuit first. It is the cheapest possible cause and takes a minute to eliminate.
- 4.Measure the heater element's resistance at the sensor connector and compare it against the specification in service data. An open reading confirms the element or the wiring between it and your meter.
- 5.Confirm supply voltage is present at the heater feed when the circuit should be commanded, and check the ground or control return for continuity.
- 6.Inspect the connector closely for a backed-out, spread or unlatched terminal, which produces an identical open-circuit result to a broken wire and is far more common after previous work.
- 7.Follow the bank 2 harness along its full length, paying particular attention to sections routed close to hot exhaust components and to any heat shield edge.
- 8.Check for corrosion under the connector seal and at the associated ground point.
- 9.Read the other stored codes and address the heater before any sensor circuit or performance code, since an element that never heats cannot report a valid value and the second code is frequently a consequence.
- 10.If supply, wiring, connector and ground all check good and the element itself reads open, replace the bank 2 sensor assembly — the heater is not separately serviceable.
Repair cost
$10 – $1,400
The bottom of the range is a fuse, and it is worth checking before anything else precisely because it occasionally is the answer. Diagnosis is $110 to $250. A connector or terminal repair runs $80 to $280 and a harness repair $100 to $450. If the heater element itself is open the whole sensor has to be replaced, as the heater is not a separate part: $250 to $900 for the sensor plus $100 to $350 in labour, with the bank 2 position usually the harder and therefore dearer of the two to reach.
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DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.