P2237: O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 1
What to do
Expect reduced power and worse economy — without a usable mixture measurement the module falls back on a fixed fuelling table rather than correcting to what the engine is actually doing. If a workshop reports testing this sensor by watching for a switching voltage on a meter, that test is not valid here. This is a wideband sensor: it does not produce a switching voltage, and a good one looks dead under that test. Ask for the air/fuel ratio or lambda value on a scan tool instead, and for the wiring and connector to be checked before the part is replaced.
What this code means
An open circuit in the positive current control line to the upstream oxygen sensor on bank 1.
Before anything else: this code tells you what kind of sensor is fitted, and that changes how it must be tested. A conventional oxygen sensor has no current control circuit, because nothing drives it. These twenty codes exist only on vehicles with a wideband sensor — often called an air/fuel ratio sensor — and confusing the two is the most common and most expensive error in this part of diagnostics.
A narrowband sensor is a battery. Its zirconia element generates its own voltage from the difference in oxygen between the exhaust and the outside air. Two signal wires and a heater, nothing driven. It swings between roughly 0.1 and 0.9 volts, and what it can actually report is only which side of the ideal mixture the exhaust is on — hence narrowband. It cannot say how rich or how lean.
A wideband sensor is not a battery, and does not produce a usable signal voltage at all. It contains a pump cell around a tiny measurement chamber, and the module drives a current through that cell to add or remove oxygen from the chamber, holding it exactly at the ideal mixture. The current required to hold it there is the measurement. Because current can flow either way and in any quantity, the sensor can report an actual ratio across a wide range rather than a switch point — which is what modern fuelling, and every lean-burn or direct-injection strategy, depends on.
Three consequences follow, and each of them costs somebody money regularly:
- The classic test does not work. Back-probing for a switching 0.1–0.9 volt signal is the standard oxygen sensor check, and on a wideband sensor it returns a nearly constant voltage that barely moves — which looks exactly like a dead narrowband sensor. Perfectly good wideband sensors are condemned this way constantly. The correct reading is the calculated air/fuel ratio or lambda value on a scan tool, or the pump current itself; not a voltage on a meter.
- A universal splice-in sensor cannot substitute for one. Those are narrowband parts. The module here is driving current through a cell and referencing it, which a generic sensor has no provision for.
- The family stops at sensor 1 for a reason. Only upstream sensors are wideband. Downstream of the catalyst the module only needs to know which side of ideal the gas is on, so a narrowband sensor is fitted there — which is why there is no positive current control code for sensor 2, and why the downstream codes look entirely different.
The fault itself is ordinary: an open in the wiring, a connector that has corroded or been disturbed, or the cell's internal connection failed. The value of the page is knowing what is on the end of the wire before testing it.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Corroded or loose connector · easy
- Faulty oxygen sensor · moderate
Less common
- Damaged wiring harness · moderate
- Incorrect oxygen sensor fitted · moderate
Rare
- Faulty engine control module · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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