EN

Severity: Low Code type: Generic (all makes)

P2237 Code: O2 Sensor Positive Current Control Circuit/Open B1S1

The wire that carries the pump current of the upstream wideband (air-fuel) sensor is open.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
O2 Sensor Positive Current Control Circuit/Open B1S1
System
Fuel & Air Metering · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$100–$600
DIY difficulty
Moderate

Bank 1 Sensor 1 on this engine is a wideband or air-fuel ratio sensor, not a classic switching O2 sensor. Inside it, a tiny measuring chamber is kept at a perfect stoichiometric balance by pumping oxygen in or out, and the current the ECM needs for that pumping is the actual measurement: about zero at a 14.7:1 mixture, positive when lean, negative when rich. The 'positive current control circuit' is the wire that carries this pump current (labelled IP or APE on Bosch-type sensors, AF+ on Denso-type sensors used by Toyota and others). P2237 means the ECM tried to drive current through it and found an open circuit: a broken conductor, a terminal that has lost contact in the connector, or an internal break in the sensor. Without the pump current the ECM has no mixture feedback, so it falls back to open-loop fueling from its maps.

Can I keep driving? The car is fine to drive for now, but the ECM runs without mixture feedback, which costs some fuel and puts extra load on the catalytic converter over time. Plan the repair within a few weeks.

How to read P2237

How to read P2237P12223374
  1. P Powertrain
  2. 2 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 37 Specific fault

Symptoms

  • Check engine light with fuel trims frozen at zero on the scan tool
  • Air-fuel ratio or lambda reading stuck at one value, often exactly 1.00 or 0 mA
  • Slightly higher fuel consumption from open-loop fueling
  • Rough or hunting idle on some engines
  • Oxygen sensor and catalyst readiness monitors stay incomplete

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Broken or high-resistance pump-current wire, typically near the connector or where the harness flexes with engine movement 28%
  2. Corroded, spread or backed-out pump-current terminal in the sensor connector 25%
  3. Internal open in the sensor's pump cell or lead 25%
  4. Harness melted against the exhaust manifold or downpipe 12%
  5. Wrong type of sensor installed during an earlier repair 5%
  6. ECM driver circuit fault 5%

Diagnosis step by step

Diagnostic flow: P22371Identify the sensor type and pinout2Inspect the connector3Check the wire end to end4Check the sensor side5Install the correct sensor6Verify closed-loop operation

  1. Identify the sensor type and pinout

    Check whether your engine uses a Bosch-style five- or six-wire wideband or a Denso/NTK-style four-wire air-fuel sensor, and find which pin is the pump current (IP/APE or AF+). Then watch live data: with an open pump circuit the lambda or current value sits frozen instead of reacting to throttle changes.

    Tools: OBD-II scanner

  2. Inspect the connector

    The sensor connector is usually clipped to the transmission bell housing, a heat shield or a bracket near the firewall. Unplug it and look for green corrosion and melted housings, then check the pump-current terminal's grip with a matching test pin.

    Tools: Flashlight, Screwdriver

  3. Check the wire end to end

    Key off, with both the ECM and the sensor unplugged, measure the pump-current wire from ECM pin to sensor connector. It should read below about 1 ohm; have a helper flex the harness along its route while you watch for the reading to jump.

    Tools: Multimeter

  4. Check the sensor side

    Measure the heater at the sensor connector; about 2–4 ohms at room temperature on most widebands tells you the sensor isn't completely burned out. Cold measurements across the pump cell aren't reliable, so if the harness tests good end to end, a known-good sensor is the definitive test.

    Tools: Multimeter

  5. Install the correct sensor

    Use the exact wideband type specified for your engine; a narrowband O2 sensor or a different wideband family won't work even if the plug fits. Apply anti-seize only if the new threads aren't pre-coated and torque to spec, typically about 30–37 lb-ft.

    Tools: O2 sensor socket, Torque wrench

  6. Verify closed-loop operation

    Clear the code and warm the engine. At idle the reading should hover around lambda 1.00 (or near 0 mA), and during a coast-down with the injectors off it should swing clearly lean; fuel trims should start moving within a few percent of zero.

    Tools: OBD-II scanner

Where the parts are

Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2) – P22371212345
Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2)
  1. 1Upstream O2 sensor
  2. 2Catalytic converter
  3. 3Downstream O2 sensor
  4. 4Diesel particulate filter
  5. 5Turbocharger

Repair options & costs

RepairDIY?Estimated cost
Repair broken wire or replace connector terminal No $100–$300
Replace upstream air-fuel sensor (aftermarket OE brand), installed Yes $180–$400
Replace upstream air-fuel sensor, dealer part No $300–$600
Replace melted harness section No $200–$500

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

With the check engine light on and the O2 sensor monitor incomplete, the car fails OBD-based state emissions tests. After the repair, drive until the O2 sensor and catalyst monitors report 'ready'.

Frequently asked questions

Is a wideband sensor different from a regular O2 sensor?

Yes. A regular sensor only switches between rich and lean, while a wideband measures the exact air-fuel ratio using a pump current. They aren't interchangeable, even if some connectors look similar.

Is P2237 the sensor or the wiring?

Both are common. Because the pump current flows through a single wire and terminal, a corroded connector or a broken strand is just as likely as a failed sensor, which is why the end-to-end resistance test comes first.

Can I use a universal sensor and splice it in?

It's possible with the right wideband type, but splices in this circuit need to be sealed and solid, since the pump current is small and the ECM also reads resistances. An original-connector sensor avoids the risk.

How much fuel will I lose?

Usually a few percent. Open-loop fueling is set slightly rich for safety, so fuel economy drops a little and the catalytic converter works harder.

Sources