When using the OBD-II (On Board Diagnostics version 2, used on all models 1996-on) fault codes to diagnose a “CHECK ENGINE” or “Service Engine Soon” light (technically, the MIL or Multi Information Lamp), the codes may use terms such as; Bank-1 or 2, Sensor-1 or 2, Sensor-A or B, etc. BMW OBD-II fault codes are thus sometimes tricky to understand.
The reason being that these terms are used can vary depending on what engine you’re working on. The Bank 1 Sensor 2 error on a BMW S65 engine won’t mean the same thing on an inline-6 engine. We’ve put together a short guide that should clear up the terminology as well as what each of these terms means on different engine architectures. Keep in mind that all information presented below applies specifically to US models.
BMW OBD II Codes — Banks?
The Bank refers to a bank of or grouping of the engine cylinders. BMW 4-cylinder engines have just one Bank while 6-cylinder, V8, V10, and V12 engines all have two Banks — Bank-1 and Bank-2. The standard rule of thumb here states that V engines have two banks, while inline engines have one. The only exception to this so-called rule is the BMW’s Inline-6 engines that also have two banks. Here’s a clear overview of what Bank applies to on various engine architectures.
- Four-cylinder engines have only one bank – Bank-1
- Six-cylinder engines have two Banks; Cylinders 1 through 3 are Bank-1 and cylinders 4 through 6 are Bank-2
- V8 engines have two Banks; Cylinders 1 through 4 (passenger side) are Bank-1 and cylinders 5 through 8 (driver side) are Bank-2
- V10 engines have two Banks: Cylinders 1 through 5 (passenger side) are Bank-1 and cylinders 6 through 10 (driver side) are Bank-2
- V12 engines have two Banks: Cylinders 1 through 6 (passenger side) are Bank-1 and cylinders 7 through 12 (driver side) are Bank-2
What Are Sensor Codes on BMW OBD II Fault Reading?
When applied to oxygen sensors, sensor 1 or 2, or sensor A or B, means the pre-cat (before the catalytic converter, Sensor-1) or post-cat (after the catalytic converter, Sensor-2) oxygen sensor. Therefore, a code of “Oxygen Sensor, Bank-2, Sensor-1” would mean that the pre-cat sensor for cylinder bank two is in question.
When applied to other sensors, solenoids, or parts on the twin cam engines (4, 6, 8, or 12 cylinder), the sensor number refers to intake or exhaust. Intake will be Sensor-1 or A, Exhaust will be Sensor-2 or B. Therefore, a code of “Camshaft Position Sensor, Bank-1, Sensor-B” would mean that the exhaust camshaft position sensor on cylinder bank one is in question.
Here’s a detailed breakdown of Bank and Sensor codes for various BMW engines.
4-Cylinder BMW Engines with Single Camshaft
All of the BMW single-cam 4-cylinder engines do not use OBD-II diagnostics and therefore, are not addressed here.
4-Cylinder BMW Engines with Two Camshafts (Twin Cam), Model Years Through 1995
All of the BMW twin-cam 4-cylinder engines through 1995 do not use OBD-II diagnostics and therefore, are not addressed here.
4-Cylinder BMW Engines with Two Camshafts (Twin Cam), Model Years Through 1996-On
- Bank – All 4-cylinder engines only have one Bank. Therefore, the Bank will always be Bank-1.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Sensor 1 or A refers to the intake side of the engine (driver side). Sensor 2 or B refers to the exhaust side of the engine (passenger side).
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor.
6-Cylinder BMW Engines with a Single Camshaft
All of the BMW single-cam 6-cylinder engines do not use OBD-II diagnostics and therefore, are not addressed here.
6-Cylinder BMW Engines with Two Camshafts (twin cam), Model Years Through 1995
All of the BMW twin-cam 6-cylinder engines through 1995 do not use OBD-II diagnostics and therefore, are not addressed here.
6-Cylinder BMW Engines with Two Camshafts (Twin Cam), Model Years 1996-On
- Bank – Cylinders 1 through 3 are Bank-1 and cylinders 4 through 6 are Bank-2.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Sensor 1 or A refers to the intake side of the engine (driver side). Sensor 2 or B refers to the exhaust side of the engine (passenger side).
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor
V8 BMW Engines, Two Camshafts (Twin Cam) Per Side (Bank), Model Years Through 1995
All of the BMW V8 engines through 1995 do not use OBD-II diagnostics and therefore, are not addressed here.
V8 BMW Engines, Two Camshafts (Twin Cam) Per Side (Bank), Model Years 1996-On
- Bank – Cylinders 1 through 4 (passenger side) are Bank-1 and cylinders 5 through 8 (driver side) are Bank-2.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Sensor 1 or A refers to the intake side of the engine (driver side), for whichever bank is being called out. Sensor 2 or B refers to the exhaust side of the engine (passenger side), for whichever bank is being called out.
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor.
V10 BMW Engines, Two Camshafts (Twin cam) Per Side (Bank)
- Bank – Cylinders 1 through 5 (passenger side) are Bank-1 and cylinders 6 through 10 (driver side) are Bank-2.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Sensor 1 or A refers to the intake side of the engine (driver side), for whichever bank is being called out. Sensor 2 or B refers to the exhaust side of the engine (passenger side), for whichever bank is being called out.
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor.
V12 BMW Engines, One Camshaft Per Side (Bank), Model Years Through 1995
All of the BMW V12 engines through 1995 do not use OBD-II diagnostics and therefore, are not addressed here.
V12 BMW Engines, One Camshaft Per Side (Bank), Model Years 1996-On
- Bank – Cylinders 1 through 6 (passenger side) are Bank-1 and cylinders 7 through 12 (driver side) are Bank-2.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Since these are single cam engines (one camshaft for each bank of the V), there will only be Sensor 1 or A when referring to sensors, solenoids, etc. This is then applied to whichever bank is being called out.
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor.
V12 BMW Engines, Two Camshafts (Twin Cam) Per Side (Bank)
- Bank – Cylinders 1 through 6 (passenger side) are Bank-1 and cylinders 7 through 12 (driver side) are Bank-2.
- Sensor, Solenoid, etc. (for all except oxygen sensors) – Sensor 1 or A refers to the intake side of the engine (driver side), for whichever bank is being called out. Sensor 2 or B refers to the exhaust side of the engine (passenger side), for whichever bank is being called out.
- Oxygen Sensors – Sensor-1 or A refers to the pre-cat sensor. Sensor-2 or B refers to the after-cat sensor.
Replacing BMW O2 Sensors and Solenoids
Often times, solving a bank or sensor code means replacing a sensor or whatever it is tasked with tracking. Considering that most of these components end up being critical for the health of your engine, it’s highly recommended that you only use Genuine BMW or quality OEM parts to replace them.
Bimmers.com offers one of the largest catalogs of BMW specific spare parts you’ll find. Head over to our store, select your car from the drop-down menu, and you’ll find parts that are a guaranteed match for your vehicle.
