OBD-II trouble code
P2240: O2 Sensor Positive Current Control Circuit/Open (Bank 2 Sensor 1)
The pump current supply to the upstream wideband sensor on bank 2 is open. The single most useful thing about this code is that the engine has a second wideband sensor still working — and that healthy sensor is a better reference than any specification table.
Quick facts
- System
- Powertrain
- Category
- Oxygen Sensor
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $120 – $1,000
- DIY difficulty
- Advanced DIY
What does P2240 mean?
This is the bank 2 counterpart to P2237. The module cannot drive current through the pump circuit of the upstream wideband sensor on bank 2, so it has no mixture measurement for that bank, drops it out of closed loop and fuels those cylinders from programmed values instead.
Before anything else, settle which physical cylinder head this code is actually talking about, because on this particular code that question costs money to get wrong. Bank 2 is defined only as the bank that does not contain cylinder number 1. Nothing in that definition says front, rear, left or right. On a transverse V6 the manufacturer's cylinder numbering decides it, and different manufacturers number in opposite directions — some start at the firewall side, some at the radiator side. Two similar-looking vehicles in the same car park can have bank 2 on opposite sides of the engine bay. Look up the numbering for the specific engine, or trace the wiring from the connector the module names, and do not decide from the shape of the exhaust manifolds. A sensor bought and fitted on the wrong head is the most common wasted afternoon on any bank 2 code.
The diagnostic advantage of a bank 2 fault, and the reason this page exists separately from P2237, is that the vehicle carries its own control experiment. Wideband pump current has no meaningful published figure. It depends on altitude, ambient temperature, fuel blend, exhaust backpressure and how long the engine has been running, so a number from a service manual is a wide envelope rather than a target. The bank 1 sensor on the same engine, in the same air, burning the same fuel, at the same second, is a far better reference. Put both banks' wideband parameters side by side on the scan tool. If bank 1 shows a live, moving pump current and bank 2 shows nothing at all, you have confirmed the fault is specific to that channel and not something environmental affecting the whole engine — and you have done it in a minute without a meter. Where a scan tool reports the actual pump current in milliamps rather than only a converted mixture ratio, that comparison is close to conclusive.
The second thing that is true of bank 2 and not of bank 1 concerns how the vehicle was built and what has been done to it since. On most assembly lines the two upstream sensors are not fitted at the same moment or by the same operation, and on a transverse engine the bank that sits against the firewall is fitted from a different access point, with a longer lead routed across the back of the engine and over the transmission. That lead passes more brackets, more heat shielding and more of the engine's rocking movement than the short front-bank run does. It is also the one disturbed by later work — anyone changing a rear-bank exhaust manifold, a starter, a rear valve cover gasket or a transmission has that harness in their way, and connectors that have been unplugged and replugged in a tight space are exactly where terminals get pushed back and pins get bent. If the vehicle has had major work in the last year, ask what was in that area before you condemn the sensor.
Everything about the small size of the current still applies. A pump cell circuit works in milliamps, which is why a joint that would run a heater or an injector without complaint can be an open circuit here. Judge terminals by their mating surfaces, not by whether the connector looks clean from outside, and treat a continuity beep as insufficient evidence.
Common causes
- Open conductor in the bank 2 pump current circuit, commonly where the longer rear-bank lead passes a bracket or heat shield
- Terminal damage in the sensor connector from earlier work in the same area — pushed-back pins, spread contacts, a partially seated lock
- Corrosion in the connector sufficient to open a milliamp circuit while still passing a continuity test
- Internal open in the sensor's pump cell or its internal bonding
- Water ingress at a low-mounted connector on the firewall side, where drainage is poorest
- Incorrect or poor-quality replacement sensor that does not match the module's pump circuit
- Sensor fitted to the wrong bank during an earlier repair, leaving the real bank 2 sensor still faulty
- Open in the module-side driver for that channel, which is uncommon and should be proved rather than assumed
Symptoms
- Check engine light with bank 2 running on programmed fuelling instead of measured mixture
- Bank 2 stuck in open loop on the scan tool while bank 1 operates normally
- No wideband mixture value, or a frozen one, for bank 2 only
- Fuel economy down, typically less dramatically than a both-banks fault
- Uneven running on cold start that settles as the engine warms
- Emissions readiness monitors that will not complete
- Bank 2 fuel trim reading zero, unavailable or obviously default
- No misfire and no serious power loss, because fallback fuelling is designed to be tolerable
Diagnostic steps
- 1.Establish which physical head is bank 2 on this engine from the manufacturer's cylinder numbering. Do not infer it from layout.
- 2.Confirm the upstream sensors are wideband, not switching. Five or six wires rather than four, and different test points entirely.
- 3.Put both banks' upstream sensor parameters on screen together and compare. A live bank 1 alongside a dead bank 2 localises the fault immediately.
- 4.Check whether the pump current itself is available as a parameter in milliamps; where it is, the healthy bank gives you the correct reference figure for today's conditions.
- 5.Ask what work has been done recently in that area of the engine, then inspect the sections of harness and the connectors that work would have disturbed.
- 6.Inspect the connector terminals themselves, pulling them where the design allows, and look at the mating faces rather than the connector shell.
- 7.Measure resistance through the pump circuit at the points the manufacturer's procedure specifies, at the module end, rather than probing the sensor side at random.
- 8.Do not apply voltage to the pump circuit or jumper it to test. That destroys wideband sensors and turns a wiring bill into a parts bill.
- 9.Only after the harness, connector and sensor have all been cleared with measurements should the module channel be considered.
Repair cost
$120 – $1,000
Diagnosis runs $100 to $250. The parts cost for an upstream wideband sensor is $80 to $350, but bank 2 labour is where this code differs from its bank 1 twin: on a transverse V6 the firewall-side sensor can take two to three times as long to reach, so fitted prices of $200 to $700 are normal and the labour can exceed the part. A harness or connector repair is $130 to $450, again access-dependent, and where the fault is a damaged terminal that repair is the correct fix rather than a new sensor. Module channel failures at $600 to $1,600 with programming are uncommon. The costliest error here is buying and fitting a sensor for the wrong bank, which pays full labour twice and fixes nothing.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with oxygen sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.