Auto Repair & Diagnostics
We test,
not guess.
Something not right? We fix that.
Expert diagnostics and repair for domestic, Asian, and European vehicles. Same-day service on most small jobs. Real testing, clear quotes, no guessing.
Trust
DMV Registered
J&N Auto is a NYS DMV-registered motor vehicle repair shop.
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What We Fix
From check engine lights to full engine repair — if it rolls, we diagnose it.
Diagnostics
Check engine light, electrical, wiring faults
Brakes & Suspension
Pads, rotors, calipers, steering
Engine Repair
Timing belts, tune-ups, internal repair
A/C & Heating
Diagnostics, repair, recharge
Electrical
Wiring, immobilizer, EVAP systems
Fluid Services
Oil changes, transmission, coolant
Ready to get it fixed?
Call, text, or fill out the form. We'll get back to you with the next appointment window.
Diagnostic Spotlight
No crank. No start.
No easy answer.
A 2012 Mini Cooper. Another shop had already replaced the starter. This is the rest of the story.
Vehicle
2012 Mini Cooper
Symptom
No crank / no start
Previous repair
Starter replaced — no change
Primary cause
Shorted DME (jump-start with broken block ground)
Secondary damage
Cylinder wash — fuel dumped during testing
Result
Running — verified, delivered
Verify
The starter was just replaced by another shop. We observed a faint clicking noise from the starter location. We sent power directly to the starter through the exciter wire — the vehicle started cranking.
Confirmed: not the starter, not load-side power, not block ground.
Isolate
Scanned the vehicle. No codes stored in the CAS (Car Access System), which sends the starter signal from the ignition. Several codes stored in the DME (Engine Control Unit). Cleared codes, tried several start attempts — no codes returned. But with the key in the ON position, several solenoids and relays were turning on and off. Scanned again — different DME codes than the first scan.
Load tested power and grounds to the DME. All checked out.
Trace
Scoped the power control side of the valvetronic system — one of the relays cycling with the key ON. The waveform spiked to almost 50 volts, and the pattern looked exactly like an injector pattern. Suspected the DME was internally shorted. Pulled the computer and sent it in for testing — confirmed, internally shorted.
Gathered more information: customer had tried jumping the car after discovering a broken block ground. Jumping with no path to ground shorts components. Root cause found.
Fix
Installed a newly cloned DME. The car cranked — but did not start. The engine had almost no cadence. Performed a compression test: every cylinder far below spec, running from 25 PSI to 60 PSI. That injector pattern we saw earlier? Every time we conducted tests with the key ON, the injectors were dumping fuel into the combustion chambers — cylinder wash.
Pulled all plugs. Soaked each piston with thin oil. Cranked engine to remove excess. Rechecked compression — it climbed, but still not enough to start. Repeated the process several times.
Prove
After completing the process several times, the car started and ran. Final repair: oil change, as it was now contaminated with fuel.
Verified start. Delivered.
Compression Test — Cylinder Pressure
After cylinder wash
After repeated oil treatment
This is the difference between replacing parts and finding the cause.
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Where we serve
By-appointment auto repair serving Long Island, NY.
Areas Covered
- Long Island
- Nassau County
- Suffolk County
- Brookhaven
- Islip
- Babylon
- Smithtown
- Huntington
Outside this area? Call us — we may still be able to help.