OBD-II trouble code
P2207: NOx Sensor Heater Control Circuit High (Bank 1)
A high reading on the bank 1 NOx heater control circuit means the commanded current never flowed — nothing on the other end drew it. Which module did the commanding matters more than it sounds: on the integrated sensors most SCR vehicles use, the heater is switched inside the sensor itself and there is no heater circuit in the harness to chase.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $15 – $1,400
- DIY difficulty
- Intermediate DIY
Browse every code in P2200–P22CA, or start from the full code library.
What does P2207 mean?
On most circuits a high code means a short to voltage. On a ground-switched heater it usually means something else, and understanding why saves a lot of wire-chasing. Whichever module is doing the switching monitors the control line. With the heater off, that line naturally sits up near supply voltage, which is normal and expected. When the heater is commanded on, the line is pulled down and the voltage should collapse as current begins to pass through the element. If the line stays up while it is being commanded down, one specific thing has been learned: the current asked for never flowed.
A load that does not draw current is a load that is not there. So a heater circuit-high code points first at a break in the path — an open element, a lost supply, a broken supply wire, a blown fuse — rather than at a wire touching battery voltage. That is close to the opposite of the intuition most people bring to a code with the word high in it.
Before that reasoning can be turned into a measurement, settle which module switched the circuit, because on most SCR-equipped vehicles it is not the engine control module. The integrated nitrogen oxide sensor carries its own control unit, that control unit drives the heater internally, and the sensor's only external connector presents battery supply, ground and a data bus — no heater feed, no heater return. The code arrives because the sensor detected the open in its own heater circuit and reported it over the bus, and the engine control module relayed it. On one of those vehicles the control line described above is inside the sealed assembly, so there is nothing in the harness to back-probe and no heater resistance to read. What is still measurable from outside is the supply, the ground, the fuse or relay behind that supply, and whether the sensor is communicating at all. Where service data does show heater pins presented at a reachable connector, everything below applies literally. Ten minutes establishing which one you have is the most useful ten minutes on this code.
This is where the code separates itself from the general open-circuit code in the same family. Both describe a break, but they are found by different means and they tend to point at different halves of the circuit. A general open code is set on a broad plausibility judgement and can arise anywhere in the loop. A circuit-high code is set specifically by the module watching its own switching behaviour and seeing no response, which puts the emphasis on the supply side and on the element itself, because those are the parts of the loop that sit between the fuse and the module's driver.
The fuse deserves a second thought rather than a quick glance. If the fuse feeding the heater has blown, the supply is gone, no current can flow when the module commands, and this code sets — but a fuse does not blow for no reason. Heater elements sometimes short internally before they fail open, drawing far more current than the circuit was designed for, taking the fuse with them and then reading as an open. Fitting a new fuse without asking why the old one failed usually buys you a second blown fuse and a repeat visit. If the fuse is shared with other heated emissions components, look for their codes too, because a set of them appearing together tells you the failure is upstream of any individual sensor.
The supply-side wiring is the other half of the search, and its geography is predictable. The feed reaches a sensor that has to live at the exhaust, so the run goes under the vehicle, through road spray and salt, past brackets and heat shields, and usually across at least one point where the exhaust moves relative to the body. Opens develop where the conductor has been fatigued by that movement or where corrosion has eaten a terminal from the inside while the outside still looks acceptable. Both are found by opening the connector properly and by moving the harness with the circuit live rather than by looking at it.
When everything upstream checks out, the element is the answer, and the cost conversation is short. There is no heater to buy on its own. The heating element, the sensing ceramic and the sensor's integrated control unit are one sealed assembly, so an open heater means a complete sensor. That is a large enough number to justify proving the fuse, the supply and the connector are healthy first, and to justify checking whether the replacement needs coding to the vehicle before it is ordered rather than after it is fitted.
One last cross-check that costs nothing. If the same vehicle has stored a heater code on a second nitrogen oxide sensor, or on an oxygen sensor, at the same time, stop looking at either sensor and look at what they share — the fuse, the relay, the supply splice or the ground. Two sensors rarely fail in the same week; one shared feed fails all the time.
Common causes
- Blown fuse or failed relay removing the supply side of the circuit
- Open or high-resistance supply wire between the fuse and the sensor connector
- Corroded terminal in the sensor connector that has eaten through from the inside while looking serviceable outside
- Conductor fatigue where the harness crosses a point at which the exhaust moves relative to the body
- Open heating element inside the sensor assembly, so no current flows when the heater is commanded on — the outcome everything above is checked in order to avoid, since it condemns the whole sealed unit
- Heater control wire shorted to a voltage source, which is the less common but genuine reading of this code where the control line runs in the harness at all
- Failed heater driver stuck in the off state, in the engine control module on the designs where it drives the heater directly and inside the sensor's own control unit otherwise
- Connector left unlatched or a pin pushed back during recent exhaust or aftertreatment work
Symptoms
- Check engine light, often with no change in the way the vehicle drives
- Nitrogen oxide data that never becomes valid because the element never reaches operating temperature
- Emissions readiness monitors that will not set, causing an inspection failure on readiness alone
- Repeated fuse failure when a shorted element took the fuse before it went open
- Heater codes on other emissions sensors at the same time when a shared feed is at fault
- Delayed start of exhaust fluid dosing on vehicles that wait for a valid signal
- Reduced power or a restriction countdown after the fault has been present for a while
Diagnostic steps
- 1.Reframe the code before testing. On a ground-switched heater, high means the commanded current never flowed, so search for a break in the path rather than for a wire touching battery voltage.
- 2.Establish from service data whether heater pins are presented at the sensor connector or whether this is an integrated assembly carrying only supply, ground and a data bus. On the integrated design there is no heater circuit in the harness, so the resistance and continuity steps below do not apply and the fault is either upstream of the supply or inside the part.
- 3.Let the exhaust cool before working at the sensor, and support the vehicle properly where it is reached from underneath. A diesel aftertreatment system runs at several hundred degrees normally and hotter still during a particulate filter regeneration, which the vehicle can begin by itself while the engine is running.
- 4.Check the fuse and relay first, and if the fuse is blown, find out why before replacing it — a heater that shorted before going open will take the new one as well.
- 5.Read every stored code. Heater faults on more than one emissions sensor point at the shared fuse, relay, splice or ground rather than at either sensor.
- 6.With the key on, confirm battery voltage is present at the supply pin of the sensor connector. Its absence puts the fault entirely upstream, on either architecture.
- 7.Where heater pins are presented at the connector, unplug it with the sensor cold and measure resistance across them, comparing against the specification for that exact part. An open reading confirms the element.
- 8.On an integrated sensor, confirm instead that the assembly is communicating. A sensor present on the bus and reporting its own heater fault is telling you the break is inside it; a sensor that is not communicating sends you back to supply, ground and the bus wiring.
- 9.Check continuity of the supply wire from the fuse to the connector, and move the harness while measuring, concentrating on points where the exhaust moves relative to the body.
- 10.Inspect the connector terminals closely for internal corrosion, since a terminal can be substantially eaten away while the visible surface still looks acceptable.
- 11.Where the engine control module drives the heater directly, test whether it is actually switching the circuit before condemning the sensor, allowing for the fact that the heater strategy ramps power in rather than applying it instantly.
- 12.Confirm any replacement sensor's coding or initialisation requirement before ordering it.
Repair cost
$15 – $1,400
A blown fuse is a few dollars and it is a real outcome on this code, particularly when several heater faults appear together. Diagnostic time is $100 to $250. Repairing an open supply wire or replacing a corroded terminal runs $120 to $450. When the element itself is open there is no partial repair, because the heater is sealed inside the assembly with the sensing ceramic and the control unit — the part is $150 to $550 and the fitted job $250 to $900, more on European, heavy-duty and coding-required applications. A failed driver inside the engine control module is the outlier at $600 to $1,800 with programming.
Estimate your repair
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Open the Repair Cost Estimator with nox sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
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.