OBD-II trouble code
P2220: NOx Sensor Heater Control Circuit High (Bank 2)
The module could not pull the bank 2 NOx sensor heater control line down when it tried. The reason this one deserves care is that the fault most likely to cause it — voltage arriving from the wrong place — is also the fault most likely to kill the output driver inside the module if the circuit is energised again before it is found.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $1,400
- DIY difficulty
- Intermediate DIY
Browse every code in P2200–P229F, or start from the full code library.
What does P2220 mean?
Nearly every heater output in a modern powertrain is switched on the ground side. The sensor gets its supply from a fuse or a relay, and the controller completes the circuit by connecting the other end of the element to chassis ground through a transistor. That layout has one consequence that explains this code entirely: when the heater is off, the control line sits close to supply voltage, and when the heater is on, it is pulled almost to zero. A high verdict therefore means the controller commanded the line down and the line stayed up.
The first thing to do with that is to notice how similar it is to the open-circuit verdict, because a good deal of wasted diagnostic effort comes from treating them as separate problems. An element that is not connected and a line the transistor could not pull down look nearly identical to a controller that can only measure the voltage in front of it. Which code you get depends on the thresholds and timing in that particular calibration rather than on what is physically wrong, which is why these two frequently appear together on one vehicle and why a repair for one usually clears both. If both are stored, you have one fault to find and not two.
Where they genuinely diverge is in the one cause that cannot produce an open reading: voltage reaching the control line from somewhere it should not. A chafe that lets the control conductor touch a live wire, a connector flooded with salt water that bridges the control pin to a permanently powered neighbour, a mis-pinned repair connector fitted the wrong way round after exhaust work — any of these hold the line up while the transistor is trying to hold it down. And that is the situation worth being careful about, because the transistor is the thing that loses. It was designed to sink the current of a heating element, not to fight a direct connection to battery voltage, and the usual outcome of a sustained argument between the two is a driver stage that no longer works at all.
So this code carries a work-order rule that its siblings do not. Find and clear the short before commanding the circuit again. Clearing the code and going for a test drive with voltage still arriving on that wire is the sequence that turns a harness repair into a module repair, and on a vehicle where the aftertreatment outputs live inside an expensive controller that is an unpleasant way to learn this.
The measurement that settles it is refreshingly simple, and it is the one place in this family where unplugging the sensor is the decisive move rather than a waste of time. With the sensor connector disconnected and the ignition on, put a meter between the control pin on the harness side and a known good ground. The controller is not commanding anything into an empty connector, so anything approaching battery voltage there is coming from the harness, and you have found your fault without needing the heater to run at all. A reading near zero, by contrast, points the investigation back at the sensor and the controller.
There is also a population pattern worth knowing. Because the leading cause is voltage arriving where it should not, this code clusters after work rather than after mileage. Exhaust or aftertreatment repairs, accident damage, rodent activity in a harness that sits in the open under the vehicle, and previous diagnostic attempts that involved jumpers or back-probe needles are all far more common histories here than gradual wear. If the light came on within a day or two of somebody working near the exhaust, start where they were working.
Finally, the practical consequence. The heater's job is to bring the sensing element up to temperature so it can read at all, so a heater that cannot be commanded means a sensor that produces no usable nitrogen oxide data, and you should expect a sensor circuit or performance code alongside this one. That companion is a symptom. Repair the heater circuit, then see what is left.
Common causes
- Control conductor shorted to a permanently powered or ignition-switched wire after chafing against a bracket, shield edge or chassis rail
- Salt water or road spray in the sensor connector bridging the control pin to an adjacent powered terminal
- Repair connector or pigtail fitted with the pins transposed during previous exhaust or aftertreatment work
- Failed output driver inside the controller, often as the consequence of an earlier short that was not cleared before the circuit was energised again
- Open element or open ground-side conductor, which many calibrations report as high rather than as open
- Corroded terminal in the control path holding enough resistance that the line cannot be pulled fully down
- Rodent damage to the aftertreatment harness where it runs exposed beneath the vehicle
- Incorrect or non-matching replacement sensor whose heater resistance is far outside what the driver stage expects
Symptoms
- Check engine light with no change in how the vehicle drives
- A bank 2 NOx sensor circuit or performance code stored alongside, caused by an element that never reaches temperature
- The bank 2 heater open-circuit code stored at the same time, which on this circuit is usually the same single fault
- Emissions readiness monitors that will not complete
- On diesels, the staged inducement sequence beginning after the fault has been present for a set distance
- A blown fuse shared with other under-vehicle circuits where the short is to a fused supply
- The fault appearing within days of exhaust, suspension or accident repair work near the harness
Diagnostic steps
- 1.Check what else is stored. The bank 2 heater open code arriving with this one usually means a single fault, so do not plan two repairs.
- 2.Ask what was done to the vehicle recently. This code follows work and damage far more often than it follows wear, and the history frequently names the location.
- 3.Disconnect the sensor and, with the ignition on, measure between the harness-side control pin and a good ground. Battery voltage in an empty connector proves the fault is in the harness.
- 4.If voltage is present, trace the control conductor for chafe points against shields, brackets and the chassis, and inspect for rodent damage where the harness runs exposed.
- 5.Unlatch and examine the connector under good light for salt, moisture and green corrosion, checking the control pin specifically rather than only the heavier supply terminals.
- 6.Repair the short before energising the circuit again. Commanding the heater with voltage still on that line is what damages the driver stage inside the controller.
- 7.With the harness proven clean, measure the heater element resistance at the sensor and compare it against the figure in the service data.
- 8.Only suspect the controller once the harness is confirmed sound, the element measures correctly, and the line still will not pull down on command.
- 9.Clear the codes and complete a full cold-start drive cycle long enough for the heater to be commanded before judging the repair.
Repair cost
$100 – $1,400
Diagnostic time runs $100 to $250, and on this code it is money well spent because the cheap outcome and the expensive one look identical at the scan tool. Repairing a chafed conductor or a corroded terminal is $80 to $350 and covers a large share of these. Replacing the sensor assembly is $250 to $900 fitted. The top of the range is the case worth avoiding: a driver stage damaged by a short that was not cleared first can mean replacing and programming the controller that owns the output, which on some diesels runs past $1,000 on its own. Finding the short before the second attempt is the difference between the two figures.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with wiring harness / circuit repair 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.