SPN 3720: Diesel Particulate Filter Active Regeneration Inhibited Due to Parking Brake Switch Active

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Understanding and Addressing Fault Code SPN 3720: A Comprehensive Guide

Fault Code SPN 3720 is a critical diagnostic indicator in modern diesel engines, specifically related to the Diesel Particulate Filter (DPF) system. This article provides an in-depth analysis of SPN 3720, its implications, and how to address it effectively.

In our workshop, we've observed that Fault Code SPN 3720 is relatively common, particularly in European heavy-duty vehicles. We've seen it frequently in Volvo and Scania trucks, as well as in some Mercedes-Benz commercial vehicles. While it does occur in American makes like Freightliner and International, and occasionally in Asian brands like Hino, our experience shows it's more prevalent in European models. The code often appears in vehicles with high mileage or those operating in dusty environments. We've noticed it's usually related to DPF ash accumulation, and in most cases, we've been able to resolve it with a DPF cleaning or replacement, followed by an ECU reset.

Urgency and Driving Implications

When SPN 3720 appears, it's generally considered an informational fault code rather than an immediate critical issue. However, the urgency depends on the associated Failure Mode Identifier (FMI):

  • FMI 0: Indicates a severe condition, requiring immediate attention
  • FMI 15: Represents a less severe condition, but still needs addressing soon

While you can continue driving with this fault code active, it's advisable to schedule service as soon as possible to prevent potential damage to the DPF system and maintain optimal engine performance.

Detailed Code Information

SPN 3720 stands for "Aftertreatment 1 Diesel Particulate Filter Ash Load Percent". It's part of the J1939 diagnostic protocol used in heavy-duty vehicles and equipment.

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Variations

The code can appear with different FMI values:

  1. SPN 3720 FMI 0: Data valid but above normal operating range – most severe level
  2. SPN 3720 FMI 15: Data valid but above normal operating range – least severe level

This code is generally associated with Cummins engines but may appear in other manufacturers' systems that use similar DPF technology.

Components Involved

The primary components associated with SPN 3720 are:

  1. Diesel Particulate Filter (DPF): Traps and removes particulate matter from exhaust gases

    • Typical size: 12-24 inches (30.5-61 cm) in length, 6-12 inches (15.2-30.5 cm) in diameter
    • Filtration efficiency: >95% of particulate matter

  2. DPF Differential Pressure Sensor: Measures pressure difference across the DPF

    • Operating range: Typically 0-100 kPa (0-14.5 psi)

  3. Engine Control Module (ECM): Monitors DPF performance and triggers fault codes

Common Causes

The most frequent reasons for SPN 3720 include:

  1. Excessive ash accumulation in the DPF
  2. Faulty DPF differential pressure sensor
  3. Clogged or damaged DPF
  4. Incomplete DPF regeneration cycles

Diagnostic Procedure

Follow these steps to diagnose SPN 3720:

  1. Connect a diagnostic tool compatible with J1939 protocol
  2. Read and record all active and stored fault codes
  3. Check the DPF ash load percentage using the diagnostic tool
  4. Inspect the DPF differential pressure sensor and its connections
  5. Perform a visual inspection of the DPF for external damage
  6. Review the vehicle's DPF regeneration history

Solutions and Repairs

Temporary Solutions

  • Perform a manual DPF regeneration if supported by the vehicle
  • Clear the fault code and monitor for reoccurrence

Permanent Solutions

  1. Replace the DPF if ash load exceeds manufacturer specifications
  2. Perform the DPF Ash Accumulator Routine in DiagnosticLink software
  3. Replace faulty DPF differential pressure sensor if diagnosed

Prevention Measures

To avoid SPN 3720:

  1. Follow recommended oil change intervals to reduce ash accumulation
  2. Ensure proper completion of DPF regeneration cycles
  3. Use high-quality diesel fuel to minimize particulate matter
  4. Avoid extended idling, which can lead to incomplete DPF regeneration

Cost Analysis

Repair Type Estimated Cost (USD) Estimated Cost (EUR)
DPF Replacement $2,000 – $5,000 €1,700 – €4,250
Sensor Replacement $200 – $500 €170 – €425
DPF Cleaning $500 – $1,000 €425 – €850

Note: Labor costs may vary by region and shop rates.

DIY Repair Guide

For skilled mechanics, here's a basic guide to replacing a DPF:

  1. Ensure the engine is cool before beginning work
  2. Locate the DPF in the exhaust system
  3. Remove any heat shields or surrounding components
  4. Disconnect the DPF sensor wiring
  5. Loosen and remove DPF mounting bolts
  6. Carefully remove the old DPF
  7. Install the new DPF, ensuring proper alignment
  8. Reconnect sensor wiring and reinstall surrounding components
  9. Use a diagnostic tool to reset the DPF ash load counter

SPN 3720 may be associated with:

Frequently Asked Questions: Fault Code SPN 3720

What does Fault Code SPN 3720 mean?

SPN 3720 stands for “Aftertreatment 1 Diesel Particulate Filter Ash Load Percent.” It indicates that the Diesel Particulate Filter (DPF) has accumulated excessive ash and may require attention.

Is it safe to continue driving with SPN 3720 active?

While you can continue driving for a short period, it’s advisable to address the issue promptly to prevent potential damage to the DPF system and maintain optimal engine performance.

What are the common FMI values associated with SPN 3720?

The most common FMI values are 0 and 15. FMI 0 indicates a more severe condition, while FMI 15 represents a less severe but still important issue.

What causes SPN 3720 to appear?

Common causes include excessive ash accumulation in the DPF, faulty DPF differential pressure sensors, clogged or damaged DPFs, and incomplete DPF regeneration cycles.

How urgent is it to address SPN 3720?

The urgency depends on the associated FMI. FMI 0 requires immediate attention, while FMI 15 should be addressed soon but is less critical.

Can I reset SPN 3720 myself?

While it’s possible to clear the code temporarily, it’s not recommended without addressing the underlying issue. The code will likely reappear if the problem persists.

What vehicles commonly experience SPN 3720?

This code is often associated with Cummins engines but can appear in various heavy-duty vehicles and equipment using similar DPF technology.

How do I diagnose SPN 3720?

Use a diagnostic tool compatible with J1939 protocol to read the code, check DPF ash load percentage, inspect the DPF and its sensors, and review the vehicle’s DPF regeneration history.

What is the typical cost to repair SPN 3720?

Costs can vary widely, from about $200-$500 (€170-€425) for sensor replacement to $2,000-$5,000 (€1,700-€4,250) for a full DPF replacement.

Can I clean the DPF instead of replacing it?

In some cases, professional DPF cleaning may be possible, costing around $500-$1,000 (€425-€850). However, if the DPF has reached the end of its service life, replacement is necessary.

What is the DPF Ash Accumulator Routine?

It’s a procedure performed using DiagnosticLink software to reset the DPF ash load counter after replacing or servicing the DPF.

How can I prevent SPN 3720 from occurring?

Follow recommended oil change intervals, ensure proper completion of DPF regeneration cycles, use high-quality diesel fuel, and avoid extended idling.

What other fault codes are often associated with SPN 3720?

Related codes may include SPN 3251 (DPF Differential Pressure), SPN 3246 (DPF Outlet Temperature), and SPN 5394 (DPF Missing Substrate).

How long does a DPF typically last?

DPF lifespan varies but can range from 100,000 to 200,000 miles (160,000 to 320,000 km) with proper maintenance.

Can I drive long distances with SPN 3720 active?

While possible, it’s not recommended. Long-distance driving with this code active may lead to reduced engine performance and potential damage to the DPF system.

Will SPN 3720 affect my vehicle’s fuel efficiency?

Yes, a clogged or malfunctioning DPF can reduce fuel efficiency and overall engine performance.

Is SPN 3720 covered under warranty?

Coverage depends on your vehicle’s specific warranty terms. Some manufacturers may cover DPF-related issues under emissions system warranties.

Can I perform a manual DPF regeneration to clear SPN 3720?

Manual regeneration may help in some cases but won’t resolve the issue if the DPF has reached its ash capacity limit. Always consult your vehicle’s manual before attempting manual regeneration.

How long does it take to replace a DPF?

DPF replacement typically takes 2-4 hours, depending on the vehicle model and technician’s experience.

Will ignoring SPN 3720 cause damage to my engine?

Prolonged neglect of this code can lead to reduced engine performance, increased fuel consumption, and potential damage to other engine components.

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