SPN 3031 – Aftertreatment 1 Outlet NOx Sensor heater issues

Introduction

Fault Code SPN 3031 indicates a malfunction with the Diesel Exhaust Fluid (DEF) tank temperature sensor circuit. While this issue requires prompt attention from a qualified mechanic, in most cases it is safe to continue driving the vehicle cautiously for a short period until a repair can be scheduled. However, ignoring the problem for an extended time can lead to more serious engine derate conditions.

Understanding SPN 3031

SPN 3031 is a manufacturer-specific diagnostic trouble code related to the DEF system. The exact definition can vary between makes and models, but it generally points to the DEF tank temperature sensor circuit.

The DEF tank contains a temperature sensor that monitors the fluid temperature and sends this data to the engine control module (ECM). The ECM uses this input to regulate DEF injection, dosing, and heating to maintain proper emissions performance.

When the ECM detects an abnormal signal from the DEF tank temperature sensor, it triggers SPN 3031 and illuminates the check engine light. The vehicle may enter a derate mode that reduces engine power if the fault persists.

Common Causes

The most frequent causes of SPN 3031, ranked from most to least common, include:

1. Faulty DEF tank temperature sensor
2. Wiring issues (short, open, high resistance) in the sensor circuit
3. Corroded or damaged wiring harness connector
4. Malfunctioning ECM (rare)

Diagnosis and Troubleshooting

To properly diagnose SPN 3031, follow these steps:

1. Connect a diagnostic scan tool and check for additional fault codes. Address other codes first if present.
2. Visually inspect the DEF tank temperature sensor wiring and connector for damage or corrosion. Repair as needed.
3. With the ignition off, unplug the sensor and measure its resistance. At 68°F (20°C), it should read around 2,500 ohms. Replace if outside specifications.
4. Check wiring continuity and resistance from the sensor connector to the ECM. Repair shorts, opens, or high resistance.
5. If the wiring and sensor test okay, suspect a faulty ECM.

Repair Solutions and Prevention

In most cases, resolving SPN 3031 requires replacing the DEF tank temperature sensor. On some models, the sensor is integrated into the DEF pump/header unit and the entire assembly must be replaced.

To replace the sensor:

1. Drain the DEF tank
2. Remove the DEF tank
3. Unplug the sensor electrical connector
4. Unscrew the sensor (or header unit) from the tank
5. Install the new sensor or assembly
6. Reinstall the tank and refill with fresh DEF

Preventative measures include:

• Keeping the DEF tank at least 1/4 full to avoid overheating the fluid
• Using only high-quality API certified DEF
• Regularly inspecting the tank, lines and components for leaks or damage

Repair Costs

Typical repair costs to resolve SPN 3031:

• DEF temperature sensor: $180-350 ($150-300 €)
• DEF header/pump assembly: $850-1,500 ($725-1,275 €)
• 1-2 hours labor: $100-250 ($85-210 €)

Exact prices vary by vehicle make, model, and location.

Associated Issues

Other fault codes that may appear with SPN 3031 include:

• SPN 1761 FMI 9 – DEF tank level sensor malfunction
• SPN 3364 FMI 9 – DEF quality sensor malfunction
• SPN 3031 FMI 4 – DEF tank temperature sensor short to ground

These codes can indicate wiring harness or connector issues that affect multiple DEF system sensors. The root cause should be thoroughly diagnosed before replacing individual components.

Frequently Asked Questions About SPN 3031

What does fault code SPN 3031 indicate?

SPN 3031 indicates a problem with the Diesel Exhaust Fluid (DEF) tank temperature sensor circuit. The sensor measures the temperature of the DEF in the tank and sends this information to the engine control module (ECM). When the ECM detects an abnormal signal from the sensor, it triggers fault code SPN 3031.

Is it safe to keep driving with an SPN 3031 code?

While SPN 3031 requires prompt diagnosis and repair, in most cases it is safe to continue driving the vehicle cautiously for a short period until service can be scheduled. However, ignoring the issue for an extended time can lead to more serious problems like engine derate or shutdown.

What are the common causes of SPN 3031?

The most frequent causes of SPN 3031, in order, are:

1. Faulty DEF tank temperature sensor
2. Wiring issues (short, open, high resistance) in the sensor circuit
3. Corroded or damaged wiring harness connector
4. Malfunctioning engine control module (ECM)

How is SPN 3031 diagnosed?

To diagnose SPN 3031:

1. Scan for additional codes and address those first
2. Visually inspect the DEF tank temperature sensor wiring and connector
3. Test the sensor resistance and replace if out of spec
4. Check wiring continuity and resistance between the sensor and ECM
5. If the wiring and sensor test okay, suspect a faulty ECM

What repairs are needed to resolve SPN 3031?

Repairs for SPN 3031 typically involve:

• Replacing the DEF tank temperature sensor (may require replacing the entire DEF pump/header unit on some models)
• Repairing damaged wiring or connectors in the sensor circuit
• Rarely, replacing a faulty ECM

How much does it cost to fix SPN 3031?

Typical repair costs for SPN 3031 are:

• DEF temperature sensor: $180-350
• DEF header/pump assembly: $850-1,500
• 1-2 hours labor: $100-250
  Exact prices vary by vehicle make, model, and location.

Can low DEF fluid cause SPN 3031?

Low DEF level itself does not directly cause SPN 3031, which indicates a problem with the DEF tank temperature sensor circuit. However, very low fluid can allow the DEF to overheat, which could lead to issues with the temperature sensor. Always keep the DEF tank at least 1/4 full.

Will disconnecting the DEF tank fix SPN 3031?

No, disconnecting or bypassing the DEF system is not a proper repair for SPN 3031 and will likely make the problem worse. The underlying cause, such as a faulty temperature sensor or wiring issue, must be diagnosed and fixed.

What other symptoms may occur with SPN 3031?

Along with the check engine light, SPN 3031 may be accompanied by:

• Other DEF system-related codes like SPN 1761 FMI 9 (DEF level) or SPN 3364 FMI 9 (DEF quality)
• Inaccurate DEF level gauge
• Engine derate (reduced power) if the fault is left unrepaired

Can you clear SPN 3031 without fixing it?

Clearing SPN 3031 without repairing the root cause is not advisable, as the code will keep returning and may escalate to engine derate. Diagnosis and repair of the underlying issue is necessary for a long-term fix.

Is there a way to bypass SPN 3031?

Some aftermarket devices claim to bypass DEF system codes like SPN 3031, but their use is not recommended. Bypassing emissions controls is illegal, can damage the SCR system, and will not resolve the actual problem causing the code. Always pursue a proper diagnosis and repair.

What does FMI mean in relation to SPN 3031?

FMI stands for Failure Mode Identifier and is an additional code that provides more detail about the specific SPN fault. For example:

• SPN 3031 FMI 3 – Voltage above normal
• SPN 3031 FMI 4 – Voltage below normal
• SPN 3031 FMI 9 – Abnormal update rate
• SPN 3031 FMI 10 – Abnormal rate of change

What is the difference between SPN and PID?

SPN (Suspect Parameter Number) and PID (Parameter Identification) are both codes used to identify specific data parameters. In the case of fault codes, SPN is the main code that identifies the general problem, while PID and FMI provide additional details. For example, SPN 3031 indicates a DEF tank temp sensor issue, while the FMI elaborates on the specific problem.

Can bad DEF fluid quality trigger SPN 3031?

Poor quality or contaminated DEF can cause problems in the SCR system, but would more likely trigger DEF quality-specific codes like SPN 3364 rather than the temperature sensor code SPN 3031. However, some sources suggest abnormal DEF temperature readings could potentially be caused by fluid issues.

What sensors are related to the DEF tank?

The main sensors associated with the DEF tank are:

1. DEF level sensor – measures the amount of fluid in the tank
2. DEF temperature sensor – measures DEF fluid temperature
3. DEF quality sensor – detects abnormal DEF concentration/contamination

Problems with these sensors can trigger codes SPN 1761 (level), SPN 3031 (temp), and SPN 3364 (quality).

Can a bad NOx sensor cause SPN 3031?

The NOx sensors measure the concentration of nitrogen oxide in the exhaust before and after the SCR catalyst. A malfunction in these sensors would more likely trigger a NOx sensor-specific code like SPN 3216 rather than the DEF temp sensor code SPN 3031. However, it's possible for multiple faults to occur together.

How does the DEF tank temperature sensor work?

The DEF tank temperature sensor is a thermistor that changes resistance based on DEF fluid temperature. It sends a voltage signal to the ECM corresponding to the measured temperature. The ECM uses this input to regulate DEF dosing, heating, and monitor for problems.

Where is the DEF tank temperature sensor located?

The DEF tank temperature sensor is typically integrated into the DEF pump/header assembly that is mounted on top of the tank. The wiring harness connects it to the ECM.

What temperature range should the DEF tank sensor read?

The normal operating temperature for DEF is between 12°F and 86°F (-11°C to 30°C). The DEF tank temperature sensor should read a value in this range, depending on conditions. Readings outside this range may trigger an SPN 3031 code.

How often should the DEF tank temperature sensor be replaced?

There is no specific service interval for the DEF tank temperature sensor. It should be replaced if it fails or gives abnormal readings that trigger an SPN 3031 code. As a preventative measure, inspect the sensor, wiring, and connector during routine DEF filter service.