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Diesel Diagnostics

Factory-level diagnostic tools and experienced technicians who know diesel systems inside and out.

Diesel engines are fundamentally different from gasoline engines — and so are their diagnostics. High-pressure fuel systems, variable-geometry turbochargers, multi-stage aftertreatment, and complex emissions controls all require specialized tools and knowledge to diagnose correctly. At Sandi Auto & Truck, we invest in factory-level scan tools for every major diesel platform so we can read the data that generic scanners miss and find the actual root cause, not just the symptom.

Why Factory-Level Tools Matter

Generic OBD-II scanners read basic codes but cannot access diesel-specific modules like aftertreatment controllers, DEF systems, or injector trim data. Our factory-level tools read every module on your truck — the same tools the dealership uses, operated by technicians with 65+ years of combined diesel experience.

Diagnostic Capabilities

Engine & Powertrain Diagnostics

Complete engine diagnostics including misfire detection, compression analysis, fuel system pressure testing, turbo boost monitoring, and crankcase pressure checks. We read and interpret OEM-level data, not just generic codes.

Emissions & Aftertreatment Diagnostics

Full diagnosis of DPF, DOC, SCR/DEF, and EGR systems. We read soot load percentages, ash accumulation data, differential pressure sensor readings, DEF quality and level, and NOx sensor output to pinpoint exactly what is failing and why.

Transmission & Drivetrain

Scan tool diagnostics for Allison 1000, Ford TorqShift, and Ram 68RFE transmissions. We monitor clutch apply pressures, shift adaptation data, torque converter performance, and solenoid function to identify shifting issues before they become major failures.

Electrical System Analysis

Advanced electrical diagnostics including circuit testing, ground fault isolation, CAN bus communication analysis, and module programming verification. Modern diesels rely on dozens of networked modules — we trace communication faults that cause intermittent and hard-to-find problems.

Fuel System Diagnostics

High-pressure fuel system testing including injector contribution rates, rail pressure analysis, CP3/CP4 pump performance, and fuel contamination checks. We identify failing injectors, pump issues, and fuel quality problems that cause hard starts, smoke, and power loss.

Preventive Diagnostic Scans

Scheduled diagnostic scans to catch developing issues before they leave you stranded. We check for stored and pending codes, monitor sensor drift, and track system trends so you can plan repairs on your schedule instead of the side of the road.

Common Diesel Trouble Codes We Diagnose

P0087

Fuel rail pressure too low

Common causes: Failing fuel pump, restricted filter, injector leak-back

P2002

DPF efficiency below threshold

Common causes: DPF clogged, soot overload, failed regen

P0299

Turbo underboost condition

Common causes: Sticking VGT vanes, boost leak, actuator failure

P20EE

SCR NOx catalyst efficiency below threshold

Common causes: DEF quality, injector failure, catalyst degradation

P0401

EGR insufficient flow

Common causes: Stuck EGR valve, clogged EGR cooler, sooted passages

P0234

Turbo overboost condition

Common causes: Wastegate stuck closed, VGT solenoid fault

These are just a few examples. We diagnose hundreds of diesel-specific fault codes across all platforms and systems.

Platforms & Scan Tools

Ford Power Stroke

Ford IDS / FDRS

Models: 6.0L, 6.4L, 6.7L, 7.3L (new)

Full module access including PCM, TCM, and aftertreatment. IPC reset, injector coding, and DPF service functions.

GM Duramax

GM GDS2 / Tech2

Models: LBZ, LMM, LML, L5P

Injector trim coding, DPF service resets, DEF system diagnostics, and TCM programming for Allison transmissions.

Ram / Cummins

wiTECH / INLINE

Models: 5.9L, 6.7L

Full Cummins engine diagnostics, aftertreatment service functions, and Chrysler body module access.

Commercial Platforms

JPRO / Noregon

Models: Freightliner, Kenworth, Peterbilt, International, Volvo, Mack

Multi-brand commercial diagnostics covering engine, transmission, ABS, and body systems across all major OEMs.

Diesel Diagnostics FAQ

Why are diesel diagnostics more expensive than gas vehicle diagnostics?
Diesel vehicles require specialized factory-level scan tools that cost $5,000-$15,000+ per platform, plus ongoing software subscriptions. Generic OBD-II scanners miss 60-70% of diesel-specific codes and cannot access aftertreatment, DEF, or advanced engine modules. You are paying for the right equipment and the expertise to interpret the data correctly.
Can a generic code reader diagnose my diesel truck?
A generic OBD-II scanner can read basic powertrain codes, but diesel trucks use manufacturer-specific protocols and modules that generic tools cannot access. DPF soot load, DEF system status, injector contribution rates, turbo position data, and aftertreatment temperatures all require factory-level or OEM-equivalent tools to read and interpret.
How long does a diesel diagnostic session take?
A standard diagnostic session takes 1-2 hours. This includes reading all stored and pending codes across all modules, reviewing freeze-frame data, performing live data monitoring, and testing suspect components. Intermittent or electrical issues may require extended diagnosis time, which we communicate upfront.
What is the difference between a code read and a full diagnostic?
A code read simply retrieves stored fault codes — it tells you what the computer flagged but not necessarily the root cause. A full diagnostic includes interpreting codes in context, performing live data analysis, cross-referencing known platform issues, and physical inspection or testing of suspect components. The code is the starting point; the diagnosis is finding the actual problem.
Do you diagnose check-engine lights caused by emissions/DEF issues?
Yes. Emissions and DEF system diagnostics are one of our specialties. We diagnose DEF quality sensor faults, NOx sensor failures, SCR catalyst efficiency codes, DPF-related codes, and EGR system problems. These issues can trigger derate or countdown-to-shutdown warnings if not addressed promptly.

Serving Willow Springs, Lemont, Burr Ridge, Hodgkins, Countryside, La Grange, Hickory Hills, Justice, Bridgeview, and the greater Chicagoland area.

Check Engine Light On?

Don't guess — get a proper diesel diagnostic. Call us today or schedule an appointment online.

Request Appointment Call (708) 839-1515