Diesel Diagnostics Checklist: What to Expect During a Full Engine Scan

Diesel Diagnostics Checklist: What to Expect During a Full Engine Scan

If your diesel truck is throwing codes, showing the dreaded "Check Engine" light, or just acting off, it’s time to get a full diagnostic scan. But what actually happens during a diesel diagnostic? What systems are tested, and how can you trust the results?

At Kash Diesel & Auto in Sicklerville, NJ, we use professional-grade diagnostic tools to evaluate Cummins, Powerstroke, and Duramax systems for daily drivers, work trucks, and fleets across the Tri-State area. Here's exactly what to expect during a diesel diagnostic—and how it helps you avoid breakdowns and unnecessary repairs.

Why Diesel Diagnostics Matter

Modern diesel trucks use complex electronic systems to manage performance, emissions, and drivability. If any sensor or component malfunctions, the ECM (engine control module) stores a diagnostic trouble code (DTC).

Diesel diagnostics are the first step in:

• Preventing costly failures
  
  
• Identifying real problems vs. false alarms
  
  
• Avoiding unnecessary part replacement
  
  
• Ensuring emissions system compliance
  
  

When to Schedule a Diagnostic Scan

• Check engine light is on (solid or flashing)
  
  
• Performance issues: rough idle, poor fuel mileage, laggy throttle
  
  
• New sounds: knocking, ticking, turbo whine
  
  
• Warning lights for DEF, DPF, or glow plugs
  
  
• Pre-purchase inspection for used diesel trucks
  
  
• After recent engine or emissions work
  
  

What Happens During a Diesel Diagnostic?

At Kash Diesel, our diesel diagnostic checklist includes:

1. OBD-II & OEM Scan

We connect a scan tool to your truck’s onboard diagnostic port to pull all active and stored DTCs. For diesel-specific systems, we use manufacturer-level software to access:

• Powertrain Control Module (PCM)
  
  
• Transmission Control Module (TCM)
  
  
• Fuel System Module
  
  
• Emissions System Module
  
  

2. Sensor Readings and Live Data

We review real-time data to check sensor accuracy:

• Boost pressure
  
  
• Exhaust gas temperature (EGT)
  
  
• Fuel rail pressure
  
  
• Turbo actuator function
  
  
• Injector balance rates
  
  
• Mass airflow (MAF) and manifold absolute pressure (MAP)
  
  

This helps identify failing sensors, clogged filters, or air/fuel imbalances.

3. Visual Inspection

Our certified techs inspect:

• Wiring harnesses and connectors
  
  
• Visible leaks (fuel, oil, coolant)
  
  
• Loose or worn hoses
  
  
• Signs of overheating or exhaust leaks
  
  

4. Emissions System Check

We evaluate all emissions-related components:

• DEF quality, tank level, and injector function
  
  
• DPF soot load and regen history
  
  
• EGR valve operation
  
  
• NOx sensor functionality
  
  

We also determine if a forced regeneration is needed.

5. Transmission & Drivetrain Evaluation

For trucks with shift concerns or drivetrain noise, we also check:

• Transmission fluid pressure
  
  
• Torque converter behavior
  
  
• Shift solenoid status
  
  
• Transfer case and axle sensors (if applicable)
  
  

6. Battery & Charging Test

We test the charging system and battery load to rule out low voltage errors that may mimic more serious faults.

Interpreting the Results

Once the scan and inspections are complete, we:

• Print and explain diagnostic codes
  
  
• Identify root causes (not just symptoms)
  
  
• Quote only needed repairs
  
  
• Advise on urgency and safety risks
  
  
• Clear codes (if appropriate) and re-scan after repairs
  
  

Common Diesel Codes We Diagnose

We also diagnose manufacturer-specific codes on:

• 6.7 Cummins (Ram HD)
  
  
• 6.6 Duramax (Chevy/GMC HD)
  
  
• 6.0/6.4/6.7 Powerstroke (Ford Super Duty)
  
  

Case Study: Ford 6.7 Powerstroke with Low Boost

A customer from Camden County brought in a 2017 F-350 with sluggish acceleration and frequent regen cycles. We scanned the truck and pulled:

• Code P0299 (underboost)
  
  
• High DPF soot load
  
  
• Low boost readings at 2,000+ RPMs
  
  

Our test revealed a sticking turbo actuator and restricted DPF. We replaced the actuator, performed a forced regen, and cleared codes. The truck regained full power and fuel economy.

FAQs: Diesel Diagnostics

How much does a diesel diagnostic cost?
At Kash Diesel, standard diagnostics start around $125 and go up depending on complexity.

Can I just clear codes myself with a scanner?
Clearing codes without fixing the root cause can hide real issues and cause worse damage. Always diagnose before clearing.

How long does a diagnostic take?
Most scans take 1–2 hours depending on systems tested. More complex issues may require extended evaluation.

Do you offer diagnostics for fleets?
Yes! We support local contractors and fleet managers with bulk pricing and fast turnaround.



Can you test deleted or tuned trucks?
We can scan and evaluate modified trucks, but we do not install or support emissions-deleted configurations (illegal in NJ/PA/DE).

Don’t Ignore the Check Engine Light

Catching diesel issues early saves thousands in repairs and keeps your truck safe and legal. Whether you're local to Sicklerville or driving in from Philadelphia or Wilmington, we're ready to help.