P205B – Reductant Tank Level Sensor Circuit Range/Performance

dhakdev

3 months ago

What is the P205B Engine Code?

The P205B code indicates a problem with the Reductant Tank Temperature Sensor 'A' Circuit Range/Performance. This code is set when the Powertrain Control Module (PCM) detects an abnormal voltage in the reductant tank temperature sensor circuit that is outside the acceptable range.

Based on our experience in the workshop, we've seen the P205B code occur fairly frequently across various European car makes, particularly in diesel models from Volkswagen, Audi, Mercedes-Benz, and BMW. We've noticed it's especially common in VW and Audi TDI engines from around 2009-2015. The issue usually stems from a faulty reductant tank temperature sensor or related wiring problems. In most cases, replacing the sensor resolves the problem, though occasionally we've had to repair wiring or replace the entire DEF tank assembly. We've found that cold weather tends to exacerbate the issue, with more cases coming in during winter months. While it can be an annoying problem for drivers, it's generally not a major repair when addressed promptly.

Urgency and Severity

A stored P205B code should be considered severe and addressed as quickly as possible. Continuing to drive with this code active could disable the Selective Catalytic Reduction (SCR) system, potentially leading to catalyst damage if not fixed promptly.

When this code appears, it's recommended to stop driving the vehicle and have it repaired immediately, either by a qualified mechanic or at a dealership. Driving should not be resumed until the underlying issue is diagnosed and resolved.

Applicability Across Vehicle Makes

The P205B code is a generic powertrain code that applies to many OBD-II compliant vehicles made from 1996 onwards. This includes vehicles from manufacturers like Mercedes, Sprinter, Ford, GMC, Chevrolet and others. However, the specific repair steps may vary based on the vehicle's year, make, model, and powertrain configuration.

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Parts Involved and Their Roles

The main component implicated in a P205B code is the reductant tank temperature sensor, also known as the Diesel Exhaust Fluid (DEF) tank temperature sensor. This sensor is typically integrated into the DEF tank reservoir assembly, similar to a fuel tank sending unit.

The reductant tank temperature sensor measures the temperature of the diesel exhaust fluid inside the tank. The PCM uses this temperature information to control the SCR system that reduces NOx emissions. If the DEF freezes due to low temperatures (below 12°F or -11°C), it cannot be injected into the exhaust stream, compromising the SCR system's effectiveness.

Common Causes

Some common causes that can trigger a P205B code include:

A faulty reductant tank temperature sensor
Wiring issues, such as damaged wires or poor connections
Problems with the PCM or SCR controller
Low DEF fluid level or contaminated/degraded DEF fluid
Extreme cold temperatures causing the DEF to freeze

Diagnosis Steps

To properly diagnose a P205B code, follow these steps:

Connect a diagnostic scanner to the vehicle's OBD-II port and retrieve all stored codes and freeze frame data. Note down the information before clearing the codes.
Conduct a test drive until the PCM enters readiness mode or the code resets. If the code resets immediately, proceed with further diagnosis. If not, it may be an intermittent issue that is harder to diagnose until the problem worsens.
Check the DEF level and quality. If the fluid is low, contaminated, or degraded, drain the tank, flush the system, and refill with fresh DEF.
Visually inspect the wiring and connectors between the reductant temperature sensor and the PCM/SCR controller. Look for any damage, corrosion, or loose connections and repair as needed.
Using a digital multimeter (DMM), test the reductant temperature sensor's resistance according to manufacturer specifications. If the readings are out of range, replace the sensor.
If the sensor tests okay but the code persists, use the DMM to check the continuity and voltage of the sensor's input and output signal circuits. Compare the readings to the manufacturer's expected values. If the circuits are faulty, repair or replace the affected wiring.

Solutions and Costs

The most common fix for a P205B code is replacing the reductant tank temperature sensor, which is often integrated into the DEF reservoir assembly. The cost of the reservoir varies by vehicle, but is typically between $500-$1000 USD ($680-$1360 EUR).

In some cases, simply cleaning the sensor and ensuring the wiring and connections are secure may resolve the issue. Wiring repairs are generally inexpensive if no components need replacing.

If the DEF fluid is frozen, thawing it out by storing the vehicle in a heated garage or using a block heater will restore SCR functionality. However, this does not address any underlying sensor faults that may have triggered the code in the first place.

Prevention

To prevent issues related to the P205B code:

Maintain proper DEF levels and only use high-quality diesel exhaust fluid from reputable suppliers.
Address any leaks in the DEF system promptly.
Keep the DEF tank and surrounding components clean and free of debris or corrosion.
Park the vehicle in a garage during extreme cold weather, if possible, to prevent the DEF from freezing.

Associated Codes and Issues

Other fault codes commonly associated with P205B include:

P20EE – SCR NOx Catalyst Efficiency Below Threshold
P2BAE – Reductant Pressure Too Low
P20E8 – Reductant Pressure Too High
P20F4 – Reductant System Performance

Issues that may appear alongside a P205B code include:

Illuminated Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL)
Reduced engine power
Increased emissions
Damaged catalytic converter or SCR catalyst
Inability to start the engine in extreme cold due to frozen DEF

By understanding the P205B code's causes, diagnostics, and solutions, vehicle owners and mechanics can quickly resolve the issue and restore proper emissions control. Regular maintenance and prompt repairs at the first sign of trouble can prevent more severe damage and costlier fixes down the line.

Frequently Asked Questions about P205B Engine Code

What does the P205B code mean?

The P205B code indicates a problem with the Reductant Tank Temperature Sensor ‘A’ Circuit Range/Performance. It means the Powertrain Control Module (PCM) has detected an abnormal voltage in the reductant tank temperature sensor circuit that is outside the acceptable range.

How serious is the P205B code?

What are the common symptoms of a P205B code?

Common symptoms include:

Illuminated check engine light
Reduced engine performance or limp mode
Increased emissions
Inability to start the engine in extreme cold

What are the common causes of a P205B code?

Possible causes include:

Faulty reductant tank temperature sensor
Wiring issues like damaged wires or poor connections
Problems with the PCM or SCR controller
Low, contaminated, or degraded diesel exhaust fluid (DEF)
Extremely cold temperatures causing the DEF to freeze

Can I still drive with a P205B code?

No, when this code appears it’s recommended to stop driving the vehicle and have it repaired immediately by a qualified mechanic or dealership. Driving should not resume until the issue is diagnosed and resolved.

Is the P205B code specific to certain vehicle makes?

No, P205B is a generic powertrain code that can occur in many OBD-II compliant diesel vehicles made from 1996 onwards. However, the exact repair steps may vary by vehicle year, make, and model.

What part is causing the P205B code?

The P205B code implicates a problem with the reductant tank temperature sensor, also known as the diesel exhaust fluid (DEF) tank temperature sensor. This sensor measures the temperature and level of the DEF.

Where is the reductant tank temperature sensor located?

The reductant tank temperature sensor is typically integrated into the DEF tank reservoir assembly, similar to a fuel tank sending unit. The DEF tank is usually located near the fuel tank.

What happens if the DEF freezes?

If the DEF freezes due to extreme cold (below 12°F or -11°C), it cannot be injected into the exhaust stream. This compromises the SCR system’s ability to reduce NOx emissions. Frozen DEF can trigger a P205B code.

How do you diagnose a P205B code?

Proper diagnosis involves these steps:

Scan for codes and document freeze frame data.
Check DEF level and quality. Replace if low or contaminated.
Visually inspect the wiring and connectors. Repair as needed.
Test the reductant temperature sensor resistance with a multimeter. Replace if faulty.
If the sensor is okay, check continuity and voltage of the sensor circuits. Repair wiring if necessary.

Can a P205B code be caused by low DEF?

Yes, if the DEF level is critically low it can cause inaccurate readings from the reductant tank temperature sensor, potentially triggering a P205B code. Always maintain proper DEF levels.

How much does it cost to fix a P205B code?

The most common repair for a P205B code is replacing the reductant tank temperature sensor, which is often part of the DEF reservoir assembly. The cost of the reservoir ranges from $500-$1000 on average. In some cases, simply cleaning the sensor and repairing the wiring may resolve the issue at minimal cost.

Can you replace just the reductant tank temperature sensor?

In most cases, the reductant tank temperature sensor is integrated into the DEF reservoir assembly and cannot be serviced separately. Usually, the whole unit needs to be replaced.

How do you clear a P205B code?

After repairing the underlying problem, the code can be cleared using an OBD-II scanner. However, if the root cause is not fixed, the code will reappear. Some vehicles may require a certain drive cycle to fully reset the code.

Can a weak battery cause a P205B code?

Indirectly, yes. A weak battery can cause low voltage in the reductant tank temperature sensor circuit, which could potentially trigger a P205B code. However, there will likely be other codes present as well. Always ensure the vehicle has a healthy, fully charged battery.

What other codes may appear with P205B?

Related codes that may appear alongside P205B include:

P20EE – SCR NOx Catalyst Efficiency Below Threshold
P2BAE – Reductant Pressure Too Low
P20E8 – Reductant Pressure Too High
P20F4 – Reductant System Performance

Can a P205B code damage the catalytic converter?

Yes, if the vehicle continues to be driven with an active P205B code, the inability to properly inject DEF can lead to damage to the SCR catalyst over time. Promptly addressing the code is important to avoid costly catalyst replacement.

How often should the DEF be topped off to prevent a P205B?

DEF is typically consumed at a rate of around 2-3% of your fuel usage. Most vehicles have a DEF tank sized to be refilled every 5,000-10,000 miles. Keeping the tank at least 1/4 full ensures you always have enough fluid for proper SCR operation. Refill the DEF at every oil change to be safe.

What is the reductant tank temperature sensor voltage range?

The acceptable voltage range varies by vehicle, but is typically between 0-5 volts. Refer to your vehicle’s service manual or wiring diagram for the exact specification. Readings outside this range will trigger a P205B.

Can extreme temperatures cause a P205B code?

Yes, while very cold temperatures below 12°F (-11°C) can cause the DEF to freeze and trigger a P205B, extremely high ambient temperatures can also cause problems. If the DEF gets too hot, it can degrade and become less effective. Avoid storing your vehicle in areas subject to extreme temperatures if possible. Park in a climate-controlled garage in severe hot or cold weather.