Diagnostic Service
Decoded, not guessed.
A check engine light is a symptom, not an answer. Pro Tech uses real diagnostic equipment and a structured process to identify root cause — then explains what we found before any work begins.
Tested, then quoted
1st
No parts swapped on a guess. We diagnose first, recommend second.
and beyond
OBD-II
Scanners, scopes, smoke machines, multimeters — the tools required to find intermittent faults.
Findings explained
100%
Every diagnostic ends with a plain-English explanation of what's wrong and what it'll take to fix.
Symptom Matcher
What's it doing?
Click a symptom to see the most common root causes and the diagnostic test we'd run. Not a substitute for a real diagnosis — but a useful starting point for the conversation.
Likely causes — Check engine light on
- 01
Failed oxygen sensor
TestRead codes + check sensor live data and switching rate.
- 02
EVAP system leak
TestSmoke test the evap system to locate the leak.
- 03
Misfire from coil or plug
TestLive data on cylinder contributions + scope ignition.
Not a diagnosis — a starting point. Bring the car in and we’ll run the actual tests.
Diagnostic Process
Five steps, then a quote.
We follow the same structured process on every diagnostic, whether it's a P-code on a Civic or an intermittent fault on a German V8.
- 01
Document conditions
Capture the symptom, when it happens, and the driving context. Read codes and freeze-frame data.
- 02
Hypothesize
Rank likely causes from most to least probable based on the symptom, codes, vehicle, and miles.
- 03
Test
Run the test that confirms or rules out the top hypothesis. Scope, smoke, multimeter, live data — whatever the test calls for.
- 04
Confirm root cause
Verify the failure with a test that wouldn't pass if the part were healthy. No 'replace and hope.'
- 05
Quote and explain
Walk you through what we found, what it'll take to fix, and what it'll cost — before any parts are ordered.
Equipment
Tools the job actually needs.
A code reader is the entry-level tool. Most real diagnostics need more.
OBD-II + manufacturer scanners
Code reading, live data, bidirectional control, manufacturer-specific systems beyond generic OBD.
Oscilloscope
For electrical faults a multimeter can't characterize — wiring, sensors, ignition signals over time.
Smoke machine
EVAP leak and intake-leak testing. Where the leak is is rarely where the code points.
Multimeter
Voltage, resistance, continuity — the everyday electrical workhorse.
Compression + leakdown
Cylinder-by-cylinder mechanical health. The difference between a fuel issue and an engine issue.
Fuel pressure
Confirming the fuel system delivers what the engine demands, under load.
What we diagnose
Every fault that ends in a code or a complaint.
Across domestic and European platforms. If your car is doing something it shouldn't, this is the page that gets you to an answer.
- Check engine codes (P-codes)
- No-start / no-crank
- Rough idle
- Misfire
- Hesitation under load
- Hard cold start
- Battery drain
- Charging system
- Starter circuit
- Alternator
- Fuel system
- Injector concerns
- EVAP leaks
- Intake leaks
- Catalytic / O2 codes
- Transmission codes
- Hard shift
- Slipping
- ABS / traction codes
- Airbag light
- HVAC failures
- AC blows warm
- Heater stays cold
- Power steering
- Suspension noise
- Brake pulsation
- Pre-purchase inspections
- European-specific faults
- Intermittent electrical
- Wiring / connector issues
From the bay — diagnostic customers
Оксана Турок
a year ago · Jeep · Headlight diagnostics
After five (!) failed attempts at different auto shops, I had almost given up on fixing the low beams on my Jeep. But then — like magic. Just two visits: accurate diagnostics, the right part ordered, quick repair — and now the lights work perfectly! The service was top-notch, and the price was a pleasant surprise. Highly recommend if you’re looking for real expertise, not just another “let’s change the bulb” approach. Also, they’re open on Saturdays — a huge plus for those of us who work all week.
FAQ
Diagnosis FAQ
How Pro Tech approaches the hard-to-find problems.
01
My check engine light is on. What does it cost to diagnose?
A basic scan reads the codes, but a real diagnostic — confirming which component actually failed, not just which one threw a code — takes time. We quote the diagnostic time upfront before we start so you know what you're committing to.
02
Another shop diagnosed my car. Will you give a second opinion?
Yes. We see this regularly with intermittent electrical and drivability concerns. Bring the prior diagnosis and any paperwork; we'll run our own tests and tell you what we find — even when it confirms the other shop was right.
03
Why do shops misdiagnose? What do you do differently?
The common failure mode is reading a code and replacing the part the code names — without verifying. We pair the code with live data, tests, and (where needed) a scope or smoke machine to confirm the actual root cause before any parts are ordered.
04
Can you diagnose intermittent problems that come and go?
Yes — these are the diagnoses most shops avoid. We document conditions, capture freeze-frame and live data, and where needed install a data logger you drive with. Intermittent doesn't mean unsolvable.
05
Do you charge for a diagnostic if I get the repair done here?
Policy varies by job complexity. For straightforward diagnostics where the repair runs in the same visit, the diagnostic time is often rolled into the repair quote. We'll be clear about it upfront — no after-the-fact surprises.
06
What kinds of diagnostic problems do you handle?
Check engine codes (P-codes), electrical faults, no-start and no-crank, drivability (hesitation, misfire, rough idle), charging system, fuel system, transmission, HVAC, and pre-purchase inspections. Domestic and European.
More services
The rest of the menu.
Brakes, suspension, engine, transmission, European
Repairs
From brake jobs to engine internals — the full mechanical menu, including Audi and other European service.
Explore RepairsOil, fluids, intervals, inspections
Maintenance
Scheduled service that protects the engine and surfaces wear before it becomes a breakdown.
Explore MaintenanceMufflers, leaks, cats, O2 sensors
Exhaust
Quiet it down and get it through inspection — exhaust repair from the manifold back.
Explore ExhaustCoding, modules, component protection
Programming
Replacement control modules sourced, installed, and coded to your VIN — including Audi/VW component protection — without the dealer visit.
Explore Programming
Book Service
Schedule the repair.
Send a few details and we'll confirm a time — usually within one business day.
- Phone
- (603) 270-5456
- Address
- 61 Elm St, Unit 5
Manchester, NH 03101 - Hours
- Mon–Fri 8:00 AM – 5:00 PM
Prefer to call? Dial (603) 270-5456 during shop hours.