Used Diesel Truck Pre-Purchase Inspection: The Checklist We Use
Updated: Sep 29
A used diesel truck can run for a very long time. It can also hide problems that a test drive won't show you. A pre-purchase inspection is how you find out which one you're buying before the money changes hands.
At Westco Automotive & Truck Repair in Colorado Springs, we inspect Ford Power Stroke, GM Duramax and Ram Cummins trucks for buyers. This is the checklist we work from. It won't tell you whether a truck is a good deal. It will tell you what condition it's in.
For the general case for inspections, see our post on why a pre-purchase inspection is crucial.
What should a diesel pre-purchase inspection include?
It should cover the engine's internal health, the fuel and emissions systems, the turbo, the cooling system, the frame, and the truck's paperwork. A gas-truck checklist misses too much. Here's what we look at.
Blow-by and crankcase pressure
Blow-by is combustion pressure that gets past the piston rings into the crankcase. Some blow-by is normal. Excessive blow-by can point to worn rings or other internal wear. We check crankcase pressure and look for signs like oil pushing out of the fill cap or breather.
Scan data
A diesel's computer records a lot about how the engine is running. Depending on the truck, we look at:
Injector balance rates (or the equivalent for that engine). Uneven readings can point to an injector that's wearing out.
Fuel rail pressure, commanded versus actual. A gap between the two can suggest a fuel supply or pump problem.
Regen history and soot load. Frequent regens can point to a sensor, EGR or driving-habit issue.
Stored and pending codes, including ones that were recently cleared.
DPF, EGR and DEF condition
On trucks equipped with them, we check the diesel particulate filter, the EGR system and the DEF (diesel exhaust fluid) system. We look for warning messages, fault codes, leaks, crystallized DEF around fittings and signs of soot where it shouldn't be.
Turbo
We check for shaft play, oil leaks, boost performance and unusual noises. Oil in the intake piping can point to turbo seal wear or excess crankcase pressure.
Cooling system
We inspect the radiator, hoses, coolant condition and the degas bottle. On some engines, coolant loss or contamination can be an early sign of a larger internal problem, so we note anything unusual.
Frame, underbody and rust
Colorado roads are commonly treated with liquid deicers such as magnesium chloride in winter. Mag chloride residue can be hard on undercarriages, brake lines, fasteners and wiring. We look at the frame, crossmembers, brake and fuel lines, and the bed and cab mounts.
VIN and title
We confirm the VIN matches across the truck and the paperwork. We also recommend running a vehicle history report and checking for open recalls on NHTSA's recall lookup.
How can you tell if a truck has been deleted, and why does it matter?
Signs of a delete often include missing or hollow emissions parts, a straight pipe where the DPF should be, blocked-off EGR components, aftermarket tuning devices, and scan data that doesn't match a factory setup. We look for all of these on every inspection.
It matters for three reasons:
It's prohibited by federal law. According to the EPA, the Clean Air Act prohibits any person from knowingly removing or rendering inoperative emissions controls on a motor vehicle, and prohibits selling or installing parts designed to defeat them. That applies to owners, not just the people who sell the parts.
Putting it back can be a big job. A deleted truck may need its emissions system rebuilt to factory function before it's legal and road-ready again.
Registration and resale. Diesels registered in parts of the Front Range, including parts of El Paso County, are in Colorado's diesel emissions program. A truck with missing emissions equipment can create headaches when you register it or sell it later.
Westco does not do emissions deletes or delete tuning, on any vehicle. If a truck we inspect has been deleted, we tell you plainly and explain what it would take to return it to factory function.
What should I watch for by engine?
Every engine family has its own patterns, and condition matters more than reputation. These are areas we pay extra attention to. None of them means a specific truck has a problem.
Ford Power Stroke
Across the 6.0, 6.4, 6.7 and 7.3 Power Stroke, we focus on coolant and oil condition, EGR and cooler health, fuel system data and regen behavior. On some Power Stroke generations, cooling and EGR issues are a known area of concern, so we look closely for coolant loss, pressure in the degas bottle, and contamination.
For a deeper look by generation, read our Ford Power Stroke buyer's guide.
GM Duramax
On Duramax trucks, we look hard at fuel system data, injector balance rates and the DEF and DPF systems. Some diesel generations use a high-pressure fuel pump design that owners watch closely. We check fuel rail pressure and fuel quality signs like water in the separator. Our post on CP4 pump failures and hidden diesel problems goes deeper on fuel pumps.
Ram Cummins
On Cummins trucks, we check blow-by, turbo condition, the emissions system on equipped models and the front-end and steering components that carry the engine's weight. Heavy towing history can show up in the transmission, so we check fluid condition and shift quality on the drive. See our Cummins diesel repair post for more.
Does Colorado require an emissions test when a diesel is sold?
In the program area, often yes. Colorado's DMV says that at the time of sale, the seller must provide the buyer with a passing emissions test that hasn't already been used to register or renew a vehicle, for vehicles that require one.
Here's how that applies around Colorado Springs, according to the Colorado DMV and the El Paso County Clerk and Recorder:
Diesel vehicles: Parts of El Paso County are in Colorado's diesel emissions program. The El Paso County Clerk and Recorder says emissions tests are required for diesel vehicles in the county.
Gas vehicles: El Paso County is not listed in the state's gas-vehicle emissions program counties.
Newer diesels: The DMV says diesel vehicles are exempt from testing for their first four model years, with an exception for a transfer of ownership in the final exempt year.
Rules can depend on the vehicle, its age and the address where it's registered, and they can change. Before you buy, check the current requirements on the Colorado DMV emissions page and the diesel vehicles page, or ask the El Paso County motor vehicle office. If you're buying from a private seller, ask for the passing test up front.
How long does the inspection take, and what do I get?
It depends on the truck and what we find. Call ahead to schedule, and we'll tell you how long to plan for when you book. The seller needs to agree to let the truck come to our shop.
You get a report of what we found. A sample report covers:
Vehicle summary: VIN, mileage, engine and transmission.
Scan results: stored, pending and recently cleared codes, plus key data like fuel rail pressure, injector readings and regen history.
Engine health: blow-by and crankcase observations, leaks, turbo condition.
Emissions system: DPF, EGR and DEF condition, and whether the factory equipment appears intact.
Cooling, fluids and drivetrain: fluid condition, hoses, transmission behavior on the drive.
Frame and underbody: rust, damage and prior repairs, with photos.
Our notes: what looks good, what needs attention now, and what to watch.
We don't tell you whether to buy. We tell you what we found, so you can make the call or negotiate with real information.
FAQ
Can you inspect a truck for sale in Pueblo or Monument?
Yes, if the seller can bring it to our shop at 1130 Valley St in Colorado Springs. We serve buyers from Fountain, Manitou Springs, Monument, Security-Widefield, Peterson SFB, Fort Carson and Pueblo.
Do you inspect Isuzu NPR box trucks too?
Yes. We service Isuzu NPR trucks and fleets, and the same approach applies: scan data, emissions system, cooling, frame and paperwork.
Should I get an inspection on a truck with low miles?
Yes. Low miles don't tell you how a truck was used. A short-trip truck can have its own emissions-system issues, and deicer exposure doesn't depend on mileage.
Bring it to Westco
Before you buy, let us look it over. Westco Automotive & Truck Repair is a female-led shop founded in 2018, with ASE-certified technicians. We're CARFAX Top Rated and RepairPal Certified, and diesel work is a core part of what we do. Learn more on our diesel service page.
We're at 1130 Valley St Ste A/B in Colorado Springs, open Monday through Friday, 9 to 5.
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Book my FREE Inspection or call (719) 591-7743.
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