OBD-II trouble code
P22A5: NOx Sensor Heater Control Circuit High (Bank 1 Sensor 2)
The rear NOx sensor heater circuit read high when it should have been pulled down. Before reaching for a meter, ask what has been done to this exhaust lately — more of these are caused by the last repair than by anything that wore out.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $0 – $1,100
- DIY difficulty
- Intermediate DIY
Browse every code in P2200–P22A8, or start from the full code library.
What does P22A5 mean?
A high reading on a heater control line means the module tried to complete the circuit and the voltage stayed up — nothing drew current. The electrical logic is simple. What makes this address worth a page of its own is where it sits in a vehicle's service history.
The sensor behind the SCR catalyst is at the far end of the aftertreatment system, and that part of the vehicle gets taken apart. Particulate filters are removed for cleaning. SCR units are replaced under warranty or at high mileage. Exhaust sections corrode and get cut out at an independent shop. Sensors of this type are routinely unplugged to reach something else. Every one of those jobs ends with a connector that has to be put back, and this code is what the vehicle says when it was not — or when it was, onto a part that does not match.
So the first three questions are historical rather than electrical. Has the exhaust been apart in the last few thousand miles? Is the connector actually latched, or resting in place looking connected? And if a sensor has been fitted, is it the right one? That last question catches more of these than people expect. Sensors of this family are sold under part numbers that differ by heater specification and by the length and routing of the pigtail, and a superficially identical unit can present the wrong load to the module, which then sees a circuit that never draws the current it commanded. A part that physically fits and reads its part number as a close match is not proof of anything; check it against the vehicle's actual specification.
When the history is clean, the fault is an open somewhere and the usual candidates apply: a broken conductor on the vehicle side, a terminal that has backed out of the connector body, a corroded pin no longer making contact, or an open heater element inside the sealed sensor. The measurement that sorts these is the same as for an open-circuit code — resistance across the heater terminals at the sensor, which should read in the single-digit to low-double-digit ohms depending on the vehicle.
There is one case where a high reading is not an open at all. If voltage is arriving on the control line from somewhere it should not, the module cannot pull the line down and reports the same fault. That is worth ruling out before condemning anything, because a feed bleeding into this circuit from an adjacent damaged wire will survive a sensor replacement and produce the identical code on the new part a week later.
Common causes
- Connector left unlatched or disconnected after particulate filter, SCR or exhaust work
- Replacement sensor of the wrong specification presenting an incorrect heater load
- Open conductor in the vehicle-side heater control wiring
- Terminal backed out of the connector body, or a pin corroded to the point of no contact
- Open heater element inside the sealed downstream sensor assembly
- Voltage feeding into the control line from an adjacent damaged circuit, preventing the module pulling it down
- Corroded or heat-damaged connector at the rear sensor position
- Failed low-side driver inside the controlling module
Symptoms
- Check engine light appearing shortly after exhaust or aftertreatment work
- Post-SCR NOx value unavailable or flagged invalid in live data
- Emissions monitors that will not complete, leaving readiness incomplete
- Exhaust fluid or emissions warning displayed alongside
- Fault returning promptly on a newly fitted sensor when the wrong part was used
- Reduced power inducement after the fault persists across several drive cycles
- No change at all in how the engine runs
Diagnostic steps
- 1.Ask what has been done to the exhaust or aftertreatment recently. A code that appeared within a few hundred miles of a filter clean, an SCR replacement or an exhaust section repair usually has its answer there.
- 2.Physically confirm the connector is latched rather than resting in place, and that it is the right connector for the right sensor. A push-fit that looks seated and is not produces exactly this code.
- 3.If a sensor has been replaced, verify the part number against the vehicle's specification rather than against physical fit. Heater specification and pigtail routing vary between parts that look identical.
- 4.Unplug the sensor and measure resistance across its heater terminals. Single-digit to low-double-digit ohms means the element is intact and the open is on the vehicle side.
- 5.Check for voltage present on the control line when none should be there. A feed bleeding in from a damaged adjacent circuit prevents the module pulling the line down and survives a sensor replacement.
- 6.Trace the vehicle-side harness for an open conductor, concentrating on sections disturbed during the recent work and on any point where the loom was re-clipped or pulled tight.
- 7.Inspect the connector terminals for a pin that has backed out of its housing and for corrosion that has ended contact without looking dramatic.
- 8.After repair, confirm the heater draws current and the sensor begins reporting a live post-SCR value rather than relying on the light going out.
Repair cost
$0 – $1,100
A genuine share of these cost nothing but the time to reconnect a connector that was left unlatched during earlier work. A connector or terminal repair is $80 to $250 and a harness repair on the vehicle side is $120 to $450. Fitting the correct sensor where an incorrect part was used is $400 to $900, plus $80 to $180 where initialisation is required — and that cost is entirely avoidable by checking the part number first. Diagnostic time is $100 to $220.
Estimate your repair
Run the numbers for your vehicle
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.