|Code||Fault Location||Probable Cause|
|P055B|| Engine Oil Pressure Sensor/Switch "B" Range/Performance |
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What Does Code P055B Mean?
OBD II fault code P055B is a generic code that is defined as, “Engine oil pressure sensor/switch B – circuit range/performance” and is set when the PCM (Powertrain Control Module) detects an abnormal or unexpected voltage or current in an electrical circuit that is associated with the oil pressure switch/sensor labeled “B”. Note that on most vehicles that use two oil pressure switches/sensors, the switch/sensor that is labeled “B” is usually the switch/sensor that monitors the lower end of the allowable oil pressure range.
NOTE #1: Note that code P055B refers specifically to an undefined or unknown failure, malfunction, or defect in one or more electrical circuits that are associated with the oil pressure switch/sensor labeled “B”, and NOT to an abnormally low engine oil pressure condition.
NOTE #2: While most modern vehicles have only one oil pressure switch/sensor that monitors the oil pressure in the engine’s lubrication system, many vehicles, such as VW and related VAG-group vehicles have two oil pressure switches/sensors. In these applications, one switch/sensor monitors the upper range of the allowable oil pressure range, while another switch/sensor monitors the lower range of the allowable oil pressure range.
NOTE #3: When the oil pressure in an engine with two oil pressure sensors falls below a minimum allowable threshold, the contacts in the switch/sensor close, which then triggers a low oil pressure warning light/message in the dashboard, as well as an audible alarm as an additional alert.
Although proper lubrication has always been important in internal combustion engines, it is greatly more so on modern engines because modern engines are not only built to closer tolerances than ever before; they also operate at higher temperatures and work at higher rotational speeds than ever before.
While many lubrication-related challenges that came with improved engine designs have been overcome with improved engine-manufacturing methods, new materials, and vastly improved engine oil formulations, the close tolerances in modern engines require relatively high oil pressures to ensure that all the moving parts in modern engines are properly lubricated. Therefore, all modern engines are fitted with at least one dedicated sensor that monitors the pressure in the lubrication system, which information it relays to the PCM continuously.
In terms of operating principles, oil pressure switches/sensors are typically either normally open or normally closed, and most are simple designs that depend on high or low oil pressure to act on an internal diaphragm to open or close a set of contact points to complete an electrical circuit. Depending on the vehicle, though, some oil pressure switches/sensors contain pressure-sensitive elements whose electrical resistance changes in response to the pressure being applied to them.
In the latter designs, the changing oil pressure produces changes in the PCM-supplied electrical current that flows through the resistive element, which changes the PCM then interprets as changes in oil pressure. Moreover, most, if not all vehicles that are fitted with oil pressure gauges in addition to oil pressure warning lights use oil pressure switches/sensors with pressure-sensitive elements.
Regardless of the design or type of oil pressure switch/sensor fitted to any given vehicle, though, the PCM on that vehicle requires valid, accurate, and plausible input data from the oil pressure monitoring system to prevent the setting of false-positive faults. Moreover, on engines that are fitted with variable valve/camshaft timing, the PCM also requires accurate input data on the oil pressure to control these functions.
Therefore, when the PCM receives implausible, unexpected, or otherwise suspect input data from the oil pressure switch/sensor, it will recognize that it cannot control one or more critically important engine control functions, it will set code P055B and illuminate a warning light as a result. Note that depending on the vehicle and the nature of the problem, multiple other trouble codes may be set, or the PCM may also initiate and maintain a limp mode or even a no-start condition to protect the engine against damage.
Where is the P055B sensor located?
This image shows the location (arrowed) of the oil pressure switch/sensor screwed into the timing cover on a 2007 Toyota Corolla engine. In most cases, the appearance of oil pressure switches/sensors follows this general pattern.
However, it should be noted that while most oil pressure switches/sensors follow this general pattern, the actual appearance and locations of these switches vary between vehicle makes and models. Some typical locations include positions on the engine block close to the oil filter, as well as locations directly on oil filter housings. In some cases, a secondary oil pressure switch/sensor may be located on the cylinder head(s). Thus, to avoid confusion, we strongly recommend that you consult reliable service information for the affected vehicles to identify and locate oil pressure switches/sensors correctly.
What are the common causes of code P055B?
NOTE: while code P055B refers specifically to a circuit fault, it is always a good idea to verify the oil pressure in the engine with a dedicated oil pressure gauge. We recognize that this is not always easy, but in some cases, circuit faults can result from failures in oil pressure sensors, so checking the actual oil pressure eliminates failed oil pressure switches/sensors as the cause of the problem. For reference purposes, the oil pressure in most light vehicles will range from about 20 to 30 psi at idling speed, to about 45 to 70 psi above about 3000 RPM.
Nonetheless, some common causes of code P055B could include one or more of the following-
- Failed or defective oil pressure switch/sensor
- Damaged, burnt, shorted, corroded, or disconnected wiring and/or electrical connectors
- In rare cases, defects and malfunctions in the PCM may cause this code, r contribute to its setting
NOTE: Low oil levels or actual low oil pressure will typically not set this code; low oil levels or low oil pressure will typically set a dedicated low oil pressure code.
What are the symptoms of code P055B?
Note that the PCM on many vehicles is programmed to take one or more actions that are aimed at preventing or limiting engine damage when oil pressure-related codes are present. While these measures are rare with codes that are not directly indicative of insufficient oil pressure, a no-start condition or even a limp mode may be present on some vehicles if any oil pressure-related codes are present.
For the most part, though, typical symptoms of code P055B could include one or more of the following-
- Stored trouble code and an illuminated warning light
- If the vehicle is equipped with an oil pressure gauge, the gauge might register no oil pressure, or maximum oil pressure at all, or only some engine speeds
- Depending on the vehicle and the exact nature of the problem, several additional codes may be present along with P055B, in which case several types of engine noise may be present, including tapping, knocking, and even grinding noises
- Code P055B will typically not cause drivability issues such as hard starting, reduced power, or increased fuel consumption unless it had been set as a result of other oil pressure related issues
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