SPN 3516: Aftertreatment 1 Diesel Exhaust Fluid Tank Level - ZIPtuning Blog (2024)

Fault code SPN 3516 indicates a problem with the Diesel Exhaust Fluid (DEF) system. The urgency of this issue depends on the Failure Mode Identifier (FMI) that accompanies the SPN code.

Urgency and Action Required

• FMI 10 (Abnormal Frequency, Pulse Width, or Period): This is a non-critical fault. You can continue driving but should address the issue soon.
• FMI 15 (Data Valid But Above Normal Operating Range – Least Severe Level): This is a moderate severity fault. Driving can continue but the issue should be diagnosed and repaired promptly.
• FMI 18 (Data Valid But Below Normal Operating Range – Moderately Severe Level): This fault is more severe. Driving should be limited and the vehicle should be serviced as soon as possible.

Note: If the DEF tank is empty or the DEF quality is very poor, the vehicle may enter a speed-limited mode or refuse to start until the issue is resolved.

Applicability and Parts Involved

SPN 3516 is a generic code that applies to various makes and models of diesel vehicles equipped with Selective Catalytic Reduction (SCR) systems, including:

• John Deere 6120M tractors
• Scania engines

The main components involved are:

• DEF tank
• DEF quality sensor
• DEF supply pump
• DEF injector
• DEF lines and heater

These components work together to inject DEF fluid into the exhaust stream, where it reacts with a catalyst to reduce NOx emissions.

Common Causes

1. Contaminated or poor quality DEF fluid
2. Debris in the DEF tank or lines
3. Faulty DEF quality sensor
4. Malfunctioning DEF heater valve
5. Damaged wiring or connectors

Diagnosis Steps

1. Check DEF concentration with a refractometer. It should be between 32.5% (eutectic point) and 35% urea by weight.
2. Inspect DEF tank and lines for debris.
3. Verify DEF heater valve is installed and operating correctly.
4. Compare DEF concentration from quality sensor to refractometer reading. They should match within 3%.
5. If sensor reading is off, inspect wiring and connectors. Repair as needed.
6. If all checks out, replace DEF quality sensor.

Repair and Prevention

• Drain and flush DEF system if fluid is contaminated or debris is found.
• Refill with high quality DEF meeting ISO 22241 standards.
• Replace faulty components as diagnosed.
• Periodically check DEF quality and level to prevent issues.

Repair Costs (USD / EUR)

• DEF quality sensor: $200-$600 / €180-€550
• DEF fluid (2.5 gal / 9.5 L): $15-$30 / €14-€28
• Labor (1-2 hours): $100-$250 / €90-€230

Other codes that may appear alongside SPN 3516 include:

• SPN 3515 (DEF Tank Temperature)
• SPN 4094 (NOx Conversion Efficiency)
• SPN 4354 (DEF Line Heater)

In our workshop, we've encountered Fault Code SPN 3516 quite frequently, especially on European diesel vehicles equipped with Selective Catalytic Reduction (SCR) systems. Just last week, we had a Volkswagen Touareg TDI in with this code. The DEF quality sensor was reading incorrectly, causing the SCR system to underdose the DEF injection. We've also seen this issue on Mercedes-Benz Sprinter vans and BMW 3-series diesels. It's not just limited to European makes though – we've diagnosed SPN 3516 on Chevrolet Silverados with the Duramax engine and even some Hyundai excavators. The common denominator seems to be contaminated or poor quality DEF fluid, but faulty sensors and wiring issues crop up too. Whenever this code appears, we know to start by checking the DEF quality and go from there.

FAQ: Fault Code SPN 3516

1. What does fault code SPN 3516 indicate?

A: SPN 3516 indicates a problem with the Diesel Exhaust Fluid (DEF) system, specifically related to the DEF tank heater, quality sensor, or fluid quality.

2. How urgent is it to address SPN 3516?

A: The urgency depends on the Failure Mode Identifier (FMI). FMI 10 is non-critical, FMI 15 is moderately urgent, and FMI 18 requires prompt service. If the DEF tank is empty or fluid quality is very poor, the vehicle may have reduced power or not start.

3. What vehicles can get SPN 3516?

A: SPN 3516 can occur on various diesel vehicles with Selective Catalytic Reduction (SCR) systems, including John Deere 6120M tractors, Hyster forklifts, and trucks with certain Cummins, Navistar, and Scania engines.

4. What are the main components related to SPN 3516?

A: The key components are the DEF tank, DEF quality sensor, DEF supply pump, DEF injector, and DEF lines and heater.

5. What are common causes of SPN 3516?

A: Common causes include contaminated or poor quality DEF fluid, debris in the DEF system, a faulty DEF quality sensor, malfunctioning DEF heater, and damaged wiring or connectors.

6. How do you diagnose SPN 3516?

A: Key diagnostic steps are:

1. Check DEF concentration with a refractometer
2. Inspect for debris in the DEF system
3. Verify DEF heater operation
4. Compare DEF quality sensor reading to refractometer
5. Inspect wiring and connectors
6. Replace DEF quality sensor if other checks are okay

7. What should the DEF concentration be?

A: The DEF concentration should be between 32.5% (eutectic point) and 35% urea by weight.

8. How do you repair SPN 3516?

A: Repairs may include draining and flushing the DEF system if contaminated, refilling with high-quality DEF, and replacing faulty components like the DEF quality sensor or heater as diagnosed.

9. How can you prevent SPN 3516?

A: Prevention involves periodically checking DEF quality and level, and only using DEF meeting ISO 22241 standards.

10. What are typical repair costs for SPN 3516?

A: Typical costs are $200-$600 for a DEF quality sensor, $15-$30 for 2.5 gallons of DEF fluid, and $100-$250 for 1-2 hours of labor.

11. What other fault codes may appear with SPN 3516?

A: Related codes can include SPN 3515 (DEF Tank Temperature), SPN 4094 (NOx Conversion Efficiency), and SPN 4354 (DEF Line Heater).

12. Can you bypass the DEF system to clear the code?

A: No, bypassing or disabling the DEF system is illegal due to emissions regulations. The underlying problem must be properly diagnosed and repaired.

13. Will adding more DEF clear the code?

A: Adding DEF will not clear the code if the problem is a faulty component or contaminated fluid. The system must be diagnosed and repaired.

14. Can you use water instead of DEF?

A: No, only use DEF meeting ISO 22241 standards. Water will damage the SCR system and cause further issues.

15. How often should you check DEF quality?

A: Check DEF quality at least every oil change or if you suspect contamination. Follow the manufacturer's recommendations.

16. What happens if you run out of DEF?

A: If the DEF tank runs empty, the vehicle will usually display warning lights, go into a speed-limited mode, and eventually not start until it is refilled.

17. How long can you drive with SPN 3516?

A: It depends on the FMI and root cause. FMI 10 is okay to drive with temporarily, but FMI 18 requires immediate service. Driving is not recommended if the DEF tank is empty or fluid quality is very poor.

18. Can poor quality DEF cause SPN 3516?

A: Yes, using contaminated or poor quality DEF is a common cause of SPN 3516. Always use DEF meeting ISO 22241 standards from a reputable supplier.

19. How do you clean the DEF system?

A: If contaminated, the DEF system should be drained and flushed according to the manufacturer's procedure, which may involve special equipment. Refill with clean, high-quality DEF.

20. Can a bad DEF quality sensor cause poor NOx conversion efficiency?

A: Yes, a faulty DEF quality sensor can read incorrect values and cause the DEF dosing to be too lean, resulting in poor NOx conversion efficiency and other issues like SPN 4094.