|Trouble Code||Fault Location||Probable Cause|
|P2237||Heated oxygen sensor (H028) 1, bank 1, positive current control - open circuit / - open circuit / - no signal||Wiring, H025 / Wiring, H025, ECM|
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What Does Code P2237 Mean?
OBD II fault code P2237 is a generic trouble code that is defined as “O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 1”, and is set when the PCM (Powertrain Control Module) detects an open circuit in or lack of a signal through the control circuit of the heater element in the oxygen sensor that is designated #1. Note that #1 oxygen sensors are always located upstream of catalytic converters, and that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.
Note also that a) the heater elements in heated oxygen sensors are typically, but not always, controlled by positive battery current, hence the reference to “positive current control” in the case of this code, and b), that the positive current to oxygen sensor heater elements is typically supplied to the sensor through a dedicated heater element relay. This also applies to air/fuel ratio sensors, which do the same thing as oxygen sensors, but in a different way.
The purpose of oxygen sensors is to provide the PCM with input data about the composition of the exhaust stream, and with particular reference to the amount of oxygen relative to ambient air. This data is used by the PCM to make suitable adjustments to the air/fuel mixture and other settings/parameters such as ignition timing, to ensure that the engine is always supplied with an air/fuel mixture that is as close to the ideal 14.7: 1 air/fuel mixture as possible.
However, since modern wide-band oxygen sensors work only when their sensing elements are at a specified temperature (typically about 1 1000F), all wide-band oxygen sensors are fitted with electronically controlled heating elements that can bring a sensor up to operating temperature in a matter of only a few seconds. Short warm-up times mean that the sensor enters closed loop operation sooner than is possible when only the heat of the exhaust stream is available as a heat source. Note that “closed-loop” operation refers to a condition where the oxygen sensor generates a signal voltage that is used by the PCM to adjust the air/fuel mixture in response to the input data from the oxygen sensor.
Until comparatively recently, the only way a PCM had of estimating the temperature of an oxygen sensor was to compare the known values of various operational parameters with values programmed into look-up tables. The obvious disadvantages of this system were that the PCM could not account for resistance variations between oxygen sensors, and that calibration of the system was complex, expensive, and inaccurate to an unacceptable degree.
To address these issues, car manufactures now use dedicated heater element control systems that are based on the resistance of the heater element, but with complex adaptive control mechanisms that can adjust the resistance of the heater element on any given oxygen sensor to eliminate sensor-to-sensor variations in resistance. Put in another way, this means that the PCM can “update” or adjust the resistance of an oxygen sensor’s heater element based on a deviation of the actual, measured resistance of the heater element from an expected, predefined (calibrated) value at engine start-up.
As a practical matter, current control to the heater element can be either through the negative or positive circuit, but in all cases, the PCM can control the current in the heater control circuit by adjusting the resistance of the heater element through a closed-loop operation. In this way, the PCM can minimize the deviation of the heater element’s actual temperature from the desired oxygen sensor temperature. The practical advantage of this system is that the PCM no longer has to calculate the temperature of an oxygen sensor based on variables it cannot control directly. Instead, the PCM can now adjust the resistance of the heater element to keep all oxygen sensors at temperatures above the required minimum operating temperature, and it can do so reliably regardless of resistance variations in between oxygen sensors in engine types that have 2 oxygen sensors designated #1- one on each bank of cylinders.
Thus, when the PCM detects an open circuit in the control circuit(s) of the upstream oxygen sensors’ heater element, it will recognize that it cannot control the fuel delivery system on the engine effectively, and it will set code P2237 and illuminate a warning light as a result.
Where is the P2237 sensor located?
The image shows the location of oxygen sensor #1 on a VW engine. Note that the oxygen or air/fuel ratio sensor designated #1 will always be located upstream of the catalytic converter on both cylinder banks 1 & 2. However, while the sensor on this application is easily accessible, on some applications the #1 oxygen sensor may be located not only under the vehicle but under heat shields and/or splash plates as well.
In these cases, it may be very difficult to inspect/test/remove/replace the #1 sensor, and it may be necessary to seek professional assistance with the diagnosis and repair of this code.
What are the common causes of code P2237?
Common causes of code P2237 are much the same across all applications, and could include one or more of the following-
- Damaged, burnt, shorted, disconnected, and corroded wiring and or connectors
- Defective oxygen or air/fuel ratio sensors
- Incorrect or unsuitable oxygen sensor or air/fuel ratio sensor in use, although it is rare for incorrect sensors to cause open circuits
- Failed or failing PCM, but since this is a rare event, the fault must be sought elsewhere before any control module is replaced
What are the symptoms of code P2237?
Typical symptoms of code 2237 are much the same across all applications, but note that the severity of one or more symptoms could vary between applications-
- Stored trouble code and illuminated MIL (CHECK ENGINE) light
- Other codes relating to fuel trims and/or misfires may be present along with P2237
- Fuel consumption may increase sharply as a result of the PCM reverting to a default fuel control mode, which typically alters the vehicles’ drivability characteristics, such as reduced power at all engine speeds and throttle settings
- Catalytic converter failure could result if the code is not resolved