SPN 3364: Diesel Exhaust Fluid (DEF) Quality

Fault code SPN 3364 indicates an issue with the quality of the diesel exhaust fluid (DEF) in vehicles equipped with selective catalytic reduction (SCR) systems. When this code appears, it’s important to address it promptly to avoid potential engine derate or shutdown. However, in most cases, you can continue driving cautiously to the nearest dealer or service center for diagnosis and repair.

Understanding SPN 3364

SPN 3364 is a manufacturer-specific diagnostic trouble code related to the SCR system. While the exact definition may vary slightly between makes and models, it generally points to improper DEF quality detected by the DEF quality sensor.

The SCR system reduces harmful nitrogen oxide (NOx) emissions by injecting DEF, a solution of 32.5% urea and 67.5% deionized water, into the exhaust stream. The DEF reacts with NOx over a catalyst, converting it into harmless nitrogen and water. Key components involved include:

• Diesel Exhaust Fluid (DEF): Reduces NOx when injected into the exhaust and reacted over the catalyst
• Selective Catalytic Reduction (SCR) System: Cleanses NOx from the exhaust using DEF
• DEF Quality Sensor: Measures DEF concentration and quality
• DEF Dosing Unit: Injects DEF into the exhaust stream
• Aftertreatment Control Module (ACM): Controls the SCR system and monitors sensors

Common Causes

Several factors can trigger an SPN 3364 fault code, including:

• Contaminated or diluted DEF fluid due to improper fluid, water, or debris in the tank
• Faulty DEF quality sensor providing inaccurate readings]
• Clogged DEF dosing unit or crystallized DEF restricting flow
• Wiring issues such as damaged circuits or loose connectors
• Failing aftertreatment control module unable to control the system properly

Diagnosis Steps

1. Check DEF concentration with a refractometer. It should read 32.5% urea. Concentrations outside the acceptable range of 28-36% will trigger SPN 3364.
2. Visually inspect all DEF lines for kinks, cracks, leaks or disconnections that could allow contaminants into the system.
3. Perform a DEF quantity test to verify proper dosing unit output. The normal volume dispensed should be between 108-132 mL (3.65-4.46 oz).
4. Inspect electrical connectors at the DEF quality sensor, dosing unit, and ACM for signs of corrosion or damage that could cause intermittent readings.
5. Use a diagnostic scan tool to monitor live DEF quality sensor data and check for additional fault codes that could help pinpoint the root cause.

Repair Solutions

• If DEF concentration is out of specification, flush the tank and refill with new, high-quality DEF fluid.
• Replace the DEF quality sensor if it fails to read the correct value after verifying good DEF in the tank].
• Clean the DEF dosing unit if partially clogged, or replace it if heavily restricted or damaged.
• Repair any damaged wiring or connectors in the DEF quality sensor, dosing unit, or ACM circuits.
• Replace the aftertreatment control module only as a last resort if no other faults are found.

Prevention

• Always use API-certified DEF from a reputable supplier to ensure quality and proper concentration.
• Avoid storing DEF for longer than 12 months, as it can degrade over time, especially in hot or cold conditions.
• Regularly maintain the DEF tank, pump, filters, and delivery lines to prevent contamination and clogging.
• Address any DEF leaks or consumption issues promptly to avoid running out of fluid unexpectedly.

Repair Costs

Diagnosing and repairing an SPN 3364 fault can vary in cost depending on the root cause and parts required. Typical costs for common repair items include:

• DEF quality sensor: $200-500 USD / €180-450 EUR
• DEF dosing unit: $500-1500 USD / €450-1350 EUR
• DEF fluid: $3-6 USD per gallon / €0.70-1.40 EUR per liter
• Shop labor rate: $80-150 USD per hour / €70-135 EUR per hour

Related Issues

SPN 3364 often appears in conjunction with other fault codes that can provide clues to the underlying problem:

• SPN 4364 FMI 18 indicates an issue with the NOx sensor readings, which could be caused by contaminated DEF
• SPN 5246 FMI 15/16 signifies an SCR system malfunction that may induce a derate or shutdown if not addressed

In some cases, problems with the EGR system, diesel particulate filter (DPF), or turbocharger can also impact SCR performance and trigger SPN 3364 indirectly. It’s important to diagnose and repair any related faults to fully resolve the issue.

Frequently Asked Questions about Fault Code SPN 3364

1. What does fault code SPN 3364 indicate?

SPN 3364 indicates an issue with the quality of the diesel exhaust fluid (DEF) in vehicles equipped with selective catalytic reduction (SCR) systems. It means the DEF concentration is outside the acceptable range of 28-36% urea.

2. How urgent is an SPN 3364 fault? Can I continue driving?

When SPN 3364 appears, it’s important to address it promptly to avoid potential engine derate or shutdown. However, in most cases, you can continue driving cautiously to the nearest dealer or service center for diagnosis and repair.

3. Is SPN 3364 a generic OBD-II code or manufacturer-specific?

SPN 3364 is a manufacturer-specific diagnostic trouble code. While the exact definition may vary slightly between makes and models, it generally points to improper DEF quality detected by the DEF quality sensor.

4. What are the key components of the SCR system related to SPN 3364?

The main SCR components involved with SPN 3364 include:

• Diesel Exhaust Fluid (DEF) tank and fluid
• DEF quality sensor
• DEF dosing unit (injector)
• Aftertreatment Control Module (ACM)

5. What are the most common causes of an SPN 3364 fault code?

Common causes that can trigger SPN 3364 include:

• Contaminated or diluted DEF fluid
• Faulty DEF quality sensor
• Clogged DEF dosing unit/injector
• Wiring issues in the DEF sensor or dosing unit circuits
• Failing aftertreatment control module

6. How do you diagnose the root cause of an SPN 3364 code?

Key diagnostic steps for SPN 3364:

1. Check DEF concentration with a refractometer (should be 32.5% urea)
2. Visually inspect DEF tank, lines, and components for damage or leaks
3. Perform a DEF quantity test to verify dosing unit output
4. Check electrical connectors and wiring for faults
5. Use a scan tool to monitor live DEF quality sensor data

7. What are the typical repair solutions for SPN 3364?

Depending on the diagnosed cause, repairs for SPN 3364 may include:

• Flushing and refilling the DEF tank with new fluid
• Replacing the DEF quality sensor
• Cleaning or replacing the DEF dosing unit
• Repairing damaged wiring or connectors
• Replacing the aftertreatment control module

8. How can I prevent SPN 3364 from reoccurring?

To avoid repeat DEF quality issues:

• Always use API-certified DEF from reputable suppliers
• Avoid storing DEF for longer than 12 months
• Regularly maintain the DEF system components
• Address any DEF leaks or consumption issues promptly

9. What are typical repair costs for SPN 3364?

Repair costs for SPN 3364 can vary widely depending on the root cause:

• DEF quality sensor: $200-500 USD / €180-450 EUR
• DEF dosing unit: $500-1500 USD / €450-1350 EUR
• DEF fluid: $3-6 USD per gallon / €0.70-1.40 EUR per liter
• Shop labor: $80-150 USD / €70-135 EUR per hour

10. What other fault codes commonly appear with SPN 3364?

SPN 3364 often appears alongside other SCR system fault codes like:

• SPN 4364 FMI 18 (NOx sensor issue)
• SPN 5246 FMI 15/16 (SCR efficiency below threshold)

11. Can bad DEF quality damage other components?

Yes, contaminated or off-spec DEF can cause deposits to form in the dosing unit, lines, and catalyst, leading to blockages and reduced NOx conversion efficiency. Always use high-quality DEF to protect the SCR system.

12. How often should I replace my DEF filter?

Most manufacturers recommend replacing the DEF filter every 150,000-200,000 miles (240,000-320,000 km) or 4,500-6,000 operating hours. Check your service manual for specific intervals.

13. What is a normal DEF consumption rate?

DEF consumption is typically about 2-3% of your diesel fuel consumption rate. For example, if your truck gets 6 mpg (2.55 km/L), it will consume about 1.5-2.0 gallons of DEF every 300 miles (483 km).

14. Can I use distilled water to dilute my DEF if the concentration is too high?

No, you should never add water or any other fluids to DEF. Doing so will contaminate it and trigger SPN 3364. If the DEF quality is off, drain and flush the tank, then refill with new DEF that meets ISO 22241 standards.

15. What happens if I run out of DEF while driving?

If the DEF tank runs empty, the engine will initially derate to about 55% power to conserve the remaining catalyst. If you continue driving without refilling the DEF, the engine will eventually derate to 5 mph (8 km/h) until the tank is refilled.

16. How long does it take for SPN 3364 to clear after repairs?

After repairs, the fault should clear after completing 3-5 drive cycles where all enabling conditions are met without fault. A “drive cycle” is an ignition-on, ignition-off sequence that allows all monitors to run. Clearing fault codes with a scan tool may also be required.

17. Can cold weather cause SPN 3364?

Extreme cold can cause DEF to freeze, which will not damage the SCR system but may trigger temporary quality faults until the fluid thaws. Most DEF systems are designed to thaw frozen DEF within 70 minutes of engine startup.

18. How do I properly store bulk DEF?

Ideal storage conditions for DEF:

• Temperature between 12-86°F (-11-30°C)
• Out of direct sunlight in opaque containers
• Vented containers to prevent pressure buildup
• Dedicated DEF equipment to avoid contamination

19. What color should healthy DEF be?

DEF should be clear or slightly yellow in color. If it appears cloudy, dark, or has a strong ammonia smell, it may be contaminated or expired and should not be used.

20. Where can I find the DEF tank on my vehicle?

The location of the DEF tank varies by make and model. It is often located near the diesel fuel tank, or in the engine compartment. Consult your owner’s manual for the exact location and capacity.