Technical Description of OBD-II Trouble Code
Circuit Range/Performance Issue with Reductant Level Sensor
What does that signify?
This is a generic diagnostic trouble code (DTC) that applies to OBD-II vehicles. It can be found in various vehicle makes such as BMW, Mercedes Benz, VW Volkswagen, Sprinter, Ford, Audi, Dodge, Ram, GMC, Chevrolet, Jeep, etc.
Did you know that the engine light illuminates when the engine’s exhaust emissions do not meet the specified standards? The ECM (Engine control module) monitors and adjusts numerous sensors, valves, systems, etc. It essentially functions as an integrated emissions testing station. It not only monitors the intake of your engine but, more importantly to the manufacturer, it monitors what your engine emits into the atmosphere.
This is relevant here because reductant level sensors are primarily found in diesel powered vehicles with a DEF (Diesel exhaust fluid) storage tank. DEF is a urea solution used in diesel engines to assist in burning exhaust, thereby reducing overall vehicle emissions, which, as mentioned earlier, is one of the most important functions of the ECM. The reductant level sensor communicates the DEF fluid level in its storage tank to the ECM.
P203B is the trouble code defined as “Reductant Level Sensor Circuit Range/Performance” and indicates that the ECM has detected an unexpected electrical reading from the sensor circuit.
A reductant DEF tank:
What is the severity of this DTC?
Considering the possibilities, I would say this is a relatively minor code. Essentially, it indicates a fault in a system that monitors what happens after the exhaust has been burned and used. However, most state/countries’ emissions standards are quite strict, so it is advisable to address this issue before it causes further harm to your vehicle and the environment!
What are some of the symptoms of the code?
Symptoms of a P203B diagnostic code may include:
What are some of the common causes of the code?
Possible causes for this P203B engine code may include:
What are some P203B diagnostic and troubleshooting steps?
The first step in troubleshooting any malfunction is to research the Technical Service Bulletins (TSB) for known issues with your specific vehicle.
Advanced diagnostic steps are highly vehicle specific and may require specialized equipment and knowledge for accurate performance. However, we provide basic steps below. For specific steps tailored to your vehicle, refer to a vehicle year/make/model/powertrain specific repair guide.
Basic Step #1
Before diagnosing any codes present, make sure to completely clear all active codes and test drive the vehicle. This will clear any codes that may have been left active after repairs or other intermittent, less important codes. After the test drive, rescan the vehicle and proceed with diagnosis using only the active codes.
Basic Step #2
If you are not already familiar with the location of the DEF (Diesel exhaust fluid) storage tank in your vehicle, take the time to locate it. It is often found in the trunk or under the vehicle. The filler neck for the storage tank should be easily accessible, either in the trunk or next to the fuel filler neck. Make sure you identify it correctly to avoid putting fluid in the wrong places. If you can mechanically check the DEF level with a dipstick, do so. However, some vehicles do not have a way to verify the DEF level other than visually inspecting the tank with a flashlight. In either case, it is important to top up the fluid, especially if P203F is present.
Basic Step #3
If your OBD2 code reader/scan tool allows it, you may be able to electronically monitor the sensor. This is particularly useful if you know the storage tank is full of DEF and the reading is indicating otherwise. In such cases, it is likely that the reductant level sensor is defective and needs to be replaced. Replacing the sensor may be challenging as it is mounted to the tank. Make sure to catch any DEF that may spill out when replacing the sensor.
Basic Step #4
If you can easily access the connector for the reductant level sensor, ensure that it is making a good electrical connection. Additionally, refer to the manufacturer’s service data for specific values and procedures to test the level sensor and confirm if it is defective before replacing it. You will likely need a multimeter for this, as resistance tests may be involved. Compare the actual values to the desired ones provided by the manufacturer. If the values are outside the specified range, the sensor will need to be replaced.
NOTE: Always follow the manufacturer’s guidelines regarding when to disconnect your battery and observe safety precautions.
Basic Step #5
Inspect the wiring harness of the reductant level sensor for any damage or chafed wires. Such damage can cause erratic values to be sent to the ECM, potentially leading to the unnecessary replacement of the sensor. Repair any bare wires or corrosion before proceeding. Ensure that the harness is securely fastened and kept away from any moving parts.
This article is intended solely for informational purposes, and the technical data and service bulletins specific to your vehicle should always take precedence.
