SPN 4337: Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit Temperature

Fault Code SPN 4337: What It Means and How to Fix It

Fault code SPN 4337 indicates an issue with the diesel exhaust fluid (DEF) system, specifically the DEF metering unit temperature sensor. When this code appears, it's important to address it promptly to avoid damage to the aftertreatment system.

Urgency and Driving Considerations

SPN 4337 is considered a moderately urgent fault. While it may be possible to continue driving for a short period, it's best to have the issue diagnosed and repaired as soon as possible. Continuing to operate the vehicle with this fault active could lead to reduced engine power, poor fuel economy, and potential damage to emissions control components.

If the check engine light is flashing, stop driving immediately and have the vehicle towed to a repair facility. A solid check engine light indicates you can drive cautiously to a shop, but don't delay getting it checked out.

Code Details and Applicability

SPN 4337 is a generic diagnostic trouble code that applies to various makes and models of diesel vehicles equipped with selective catalytic reduction (SCR) systems. The code definition is consistent across manufacturers, but the exact repair procedure may vary slightly depending on the specific vehicle.

The code indicates a problem with the DEF metering unit temperature sensor, which is responsible for monitoring the temperature of the DEF being injected into the exhaust stream. If the sensor readings are out of the expected range, the engine control module (ECM) will log the fault and trigger the check engine light.

Related Components and Their Functions

The main components involved when SPN 4337 is triggered are:

• DEF Metering Unit: Injects a precise quantity of DEF into the exhaust based on operating conditions. The metering unit includes a temperature sensor to ensure the DEF is at the optimal temperature for injection.

• DEF Tank and Supply Lines: Store and transport DEF from the tank to the metering unit. Crystallized DEF in the lines can cause blockages and lead to issues with the metering unit.

• DEF Temperature Sensor: Measures the temperature of the DEF in the metering unit. If the sensor fails or reads out of range, it can cause the metering unit to inject an incorrect amount of DEF.

Common Causes

Some of the most common causes of SPN 4337 include:

1. Faulty DEF metering unit temperature sensor
2. Wiring issues between the sensor and ECM
3. Crystallized DEF clogging the metering unit or supply lines
4. Low DEF level or contaminated DEF in the tank
5. Malfunctioning DEF pump or pressure limiting valve

Diagnosis and Troubleshooting Steps

To properly diagnose SPN 4337, follow these steps:

1. Scan for additional fault codes. SPN 4334 (DEF delivery issue) and SPN 4335 (DEF pressure issue) often appear alongside SPN 4337.

2. Check the DEF level and quality. If the DEF is low, contaminated, or crystallized, it can cause metering unit issues.

3. Inspect the DEF tank, pump, and supply lines for leaks, blockages, or crystallization. Clean or replace components as needed.

4. Test the DEF metering unit temperature sensor using a multimeter. At room temperature (20°C/68°F), the sensor should read around 2.5 kΩ. If the readings are out of specification, replace the sensor.

5. Check the wiring and connectors between the sensor and ECM for damage, loose connections, or corrosion. Repair wiring issues as necessary.

6. If the sensor and wiring are in good condition, the DEF metering unit itself may be faulty and require replacement.

Repair Costs and Prevention

The cost to diagnose and repair an SPN 4337 fault can vary depending on the root cause and the specific vehicle. On average, expect to pay between $100-$200 USD (€85-€170 EUR) for diagnosis and $300-$800 USD (€255-€680 EUR) for parts and labor to replace a faulty DEF metering unit or temperature sensor.

To prevent issues with the DEF system and avoid SPN 4337, follow these tips:

• Maintain proper DEF levels and only use high-quality DEF that meets ISO 22241 standards
• Address any DEF-related fault codes promptly to prevent component damage
• Keep the DEF tank and supply lines clean and free of contamination
• Regularly inspect the DEF system for leaks or signs of crystallization

By understanding fault code SPN 4337 and taking proactive steps to maintain your vehicle's DEF system, you can minimize repair costs and keep your diesel engine running efficiently.

Frequently Asked Questions About Fault Code SPN 4337

What does fault code SPN 4337 mean?

Fault code SPN 4337 indicates an issue with the diesel exhaust fluid (DEF) system, specifically a problem with the DEF metering unit temperature sensor circuit. This sensor monitors the temperature of the DEF being injected into the exhaust stream.

How urgent is it to address SPN 4337?

SPN 4337 is moderately urgent. While it may be possible to drive short distances with the fault active, it's best to diagnose and repair the issue promptly to avoid potential damage to emissions control components and prevent the engine from entering a reduced power mode.

What are the probable causes of SPN 4337?

The most likely causes of SPN 4337 are:

1. Faulty DEF metering unit temperature sensor
2. Issues with the wiring or connector for the temperature sensor
3. Crystallized DEF clogging the metering unit

Can SPN 4337 be caused by low DEF levels?

Yes, low or contaminated DEF can lead to crystallization that clogs the metering unit and triggers SPN 4337. Always maintain proper DEF levels using a high-quality fluid that meets ISO 22241 standards.

What other components are involved when diagnosing SPN 4337?

In addition to the DEF metering unit and temperature sensor, other related components include:

• DEF tank, pump, and supply lines
• Pressure limiting valve
• Wiring between the sensor and engine control module (ECM)

Are there any other fault codes that often appear with SPN 4337?

SPN 4334 (DEF delivery issue) and SPN 4335 (DEF pressure issue) frequently occur alongside SPN 4337. Addressing these related faults is key to properly diagnosing and repairing the root cause.

What are the typical enabling conditions for SPN 4337?

SPN 4337 is triggered when the DEF temperature sensor signal falls below the expected range, indicating a circuit failure or excessively low reading from the sensor itself.

How do you troubleshoot SPN 4337?

To diagnose SPN 4337:

1. Scan for additional codes like SPN 4334/4335
2. Check DEF level and quality
3. Inspect DEF system for leaks or crystallization
4. Test the temperature sensor and wiring
5. Replace faulty components as needed

What tools are needed to diagnose SPN 4337?

Diagnosing SPN 4337 requires:

• A diagnostic scan tool to read fault codes
• A digital multimeter to test the temperature sensor and wiring
• Basic hand tools to remove and inspect DEF system components

How do you test the DEF metering unit temperature sensor?

Using a multimeter, check the resistance of the temperature sensor at room temperature (20°C/68°F). It should read around 2.5 kΩ. Readings significantly outside this range indicate a faulty sensor that needs replacement.

What is the typical repair cost for SPN 4337?

The cost to diagnose and repair SPN 4337 varies based on the root cause, but on average it ranges from $100-$200 USD (€85-€170 EUR) for diagnosis and $300-$800 USD (€255-€680 EUR) for parts and labor to replace the DEF metering unit or temperature sensor.

Can SPN 4337 cause the engine to shut down?

Yes, if SPN 4337 is not addressed promptly, it can lead to engine derate and eventual shutdown to protect the aftertreatment system from damage due to improper DEF dosing.

How can I prevent SPN 4337 from occurring?

To avoid SPN 4337 and related DEF issues:

• Maintain proper DEF levels with a high-quality fluid
• Address any DEF-related fault codes promptly
• Keep the DEF system clean and free of contamination
• Regularly inspect for leaks or crystallization

What is the difference between SPN 4337 FMI 3 and FMI 4?

SPN 4337 FMI 3 indicates a DEF metering unit temperature sensor drift, meaning the sensor readings are out of the expected range. FMI 4 signifies the sensor circuit has failed low, often due to wiring issues or a faulty sensor.

Can cold weather cause SPN 4337?

Extremely cold temperatures can cause DEF to crystallize and clog the metering unit, potentially triggering SPN 4337. However, most modern DEF systems are designed to handle cold weather and prevent freezing down to -11°C (12°F).

Will adding anti-gel to my DEF tank prevent SPN 4337?

No, never add any additives or anti-gel to your DEF tank. Doing so will contaminate the fluid and can cause issues like SPN 4337. Only use pure, high-quality DEF that meets ISO 22241 standards.

Is SPN 4337 specific to certain engine makes and models?

No, SPN 4337 is a generic fault code that can appear on various diesel engines equipped with selective catalytic reduction (SCR) systems for emissions control. The exact troubleshooting and repair process may vary slightly by manufacturer.

How often should I check my DEF system to prevent issues like SPN 4337?

Inspect your DEF system, including the tank, pump, lines, and sensors, at every oil change or every 5,000 miles (8,000 km), whichever comes first. Address any leaks, contamination, or fault codes promptly to avoid more serious issues.

Can I drive my vehicle with SPN 4337 active?

It's best not to drive with SPN 4337 active, as it can lead to engine derate, increased emissions, and potential damage to the aftertreatment system. If the check engine light is flashing, stop driving immediately and have the vehicle towed for diagnosis and repair.

What should I do if SPN 4337 keeps coming back after repairs?

If SPN 4337 reappears after initial repairs, there may be an underlying issue that was not addressed, such as contaminated DEF, leaking components, or wiring problems. Perform a thorough diagnosis and consult with a qualified technician familiar with emissions systems to identify and fix the root cause.