How to Diagnose and Fix Cummins Fault Code 1921

Cummins is arguably considered the powerhouse behind some of the most hardworking heavy-duty engines. At the heart of this muscular performance lies an intricate network of sensors and signals, such as fault codes. Today we'll be specifically covering Cummins Fault Code 1921, guiding you through the diagnosis and repair process.

Understanding Cummins Fault Code 1921

Fault code 1921 is an important flag for Cummins engines. It indicates elevated soot levels in the after-treatment particulate filter, which — if left unaddressed — can negatively impact your engine's performance. This fault code is usually triggered by issues with sensors, wiring problems, or specific engine parameters. Common symptoms of this fault code include performance issues and dashboard alerts.

Tools and Materials for Solving Fault Code 1921

Jaltest is your biggest ally for complex issues such as filter malfunctioning. Jaltest is a cutting-edge, multi-brand diagnostic software with excellent coverage for the Cummins brand of engines. 

For better troubleshooting, have a multimeter and a sturdy wrench set on hand to make immediate adjustments and quick fixes when applicable. 

Alternatively, you can try using Cummins’ brand-specific diagnostic tool: INSITE and QuickServe (QSOL).

Learn how to use Cummins INSITE & QSOL like a pro with our affordable, expert-led online courses! With more experience, you can solve simple fault codes, such as fault code 1921, with ease. Expand your understanding of datalink today.

Step-by-Step Diagnosis Decoding

Step 1: Inspecting Wiring and Connectors

The journey to a healthy engine begins with the sensors. Locate them, and perform a meticulous visual inspection of the wiring and connectors associated with this fault code. Be on the lookout for any visible damage, corrosion, or loose connections. These may seem like tiny issues, but they make a massive impact. 

Step 2: Testing the Sensors

Grab a multimeter and  check the resistance and voltage readings of the related sensors. Keep the manufacturer's specifications in sight to identify any discrepancies in the readings.

Step 3: Reviewing Engine Control Module (ECM) Settings

Your ECM governs the actions of your engine. Using Jaltest, sift through the ECM data and ensure the parameters align with your Cummins engine model. This tiny check can ward off unnecessary confrontations with Code 1921.

Step 4: Repairing or Replacing Damaged Wiring and Connectors

With the culprit exposed, it's time to restore your engine to perfect health. Repair the damaged wiring efficiently using techniques such as soldering or crimping. If they're beyond repair, consider a replacement to avoid future engine woes.

Step 5: Replacing Faulty Sensors

Need to replace a sensor? Remember that an essential quality replacement here can save you other headaches down the line. Follow the manufacturer guidelines for proper removal and installation.

Step 6: Reprogramming the ECM (If Required)

In some cases, ECM reprogramming might be necessary. Though reprogramming might sound complicated, Jaltest ensures this step is completed accurately and safely, protecting you from any missteps.

Step 7: Ensuring Functionality Post-Repair 

Repair done? Fire up the engine, listen to its heartbeat for a few minutes, and check its performance with a test ride. Call upon Jaltest for a final diagnostic scan. If all checks out, fault code 1921 is cleared. 

How to Clear Cummins Fault Code 1921

Step 1: Initiate a Stationary Regeneration

Utilize Cummins INSITE or a comparable tool to initiate a stationary (parked) regeneration. This is the appropriate maintenance action for the current soot levels.

Step 2: Verify After Successful Regeneration

If the soot load falls below the specified threshold, the ECM diagnostic will pass, resulting in the lamp turning off and the Check Engine light being cleared.

Step 3: Manually Clear Fault Codes

After soot levels normalize, employ INSITE’s “Reset All Faults” option to remove any active or inactive codes.

Step 4: Examine Underlying Issues if the Code Reappears

Light-duty operation may not produce sufficient heat for passive regeneration, so you should consider enhancing the operational load.

Inspect for excessive soot generation stemming from engine problems or inefficient fuel combustion.

Why Won’t Cummins Fault Code 1921 Clear?

If the code is not clearing automatically, you may need to do a diagnostic reset using a tool like Jaltest.

However, if the code still reappears after a full reset, that is usually an indicator that the soot levels are still too high. Try recleaning and regenerating the aftertreatment system before clearing the code again.

How to Prevent Cummins Fault Code 1921

You can take proactive steps to prevent Cummins fault code 1921 by addressing soot build-up before it becomes a serious issue. By adopting these simple but effective habits, you can ensure you never see the fault code again.

• Stop Excessive Idling

  • Idling is one of the leading causes of soot build-up because exhaust temps stay too low to trigger passive regeneration.

  • If members of your team are idling unnecessarily, make sure to alert your team of the issue and retrain them to avoid it.

  • Setting up idle shutdown timers also makes a big difference.

• Allow Passive and Active Regeneration

  • Soot is burnt off automatically through active and passive regeneration, which prevents build-up that triggers the 1921 error code.

  • Short trips, low load driving, and cool temperatures can cause regeneration to fail, allowing soot to build up.

  • To prevent interrupting the automatic regeneration, you need to regularly drive at highway speeds with moderate-to-high engine load.

• Perform Stationary Regens When Needed

  • If passive regeneration is not finishing the job, don’t be afraid to schedule stationary regens (even if it does mean there will be some downtime involved). Especially if you see DPF lamps or a Check Engine light.

• Ensure Sensors are Clean and Dry

  • Water or soot in the sensor lines can trigger false readings.

  • Take the time to inspect the sensors regularly and replace them when needed.

Full Circle: Learning and Forwarding

There is an understated value in prompt, proactive engine maintenance. Staying ahead of these fault codes translates to longer engine life and enhanced performance.

Jaltest unravels the complexities of these fault codes and energizes your journey from diagnosis to resolution. We encourage all our readers to deploy this multi-brand diagnostic tool. Intrigued? For a hands-on understanding of Jaltest, we're happy to offer a demo.