ISSUE 036Buyer Brief
Can you tell if a used car's check-engine codes were cleared?
Sometimes the scan leaves clues, but it cannot prove who cleared the codes or why. Check readiness, permanent codes, MIL status, and scan completeness before buying.
CAR ANSWERS · NO PARTS GUESSINGWarning light or code?
Warning light or code?
Pick what you see.
Get a direct answer, what the warning or code does not prove, and the next useful check. Start with the problem in front of you.
LATEST ANSWERS · MONDAY / WEDNESDAY / FRIDAYUseful enough to save.
Useful enough to save.
Specific enough to test.
Each answer separates observed facts, possible causes, missing evidence, and the next useful test. New work publishes Monday, Wednesday, and Friday only when it passes review.
Follow the free RSS feedISSUE 035Buyer Brief
Can you pass emissions with one readiness monitor not ready?
Sometimes—but not everywhere. The allowed number and type of incomplete OBD readiness monitors depend on the vehicle and the current rules where it is tested.
ISSUE 034Buyer Brief
Will my car pass emissions with the check-engine light on?
A lit check-engine light usually means an OBD-based emissions test will not pass, but readiness, communication, permanent codes, and local rules also matter. Learn what to check before the inspection lane.
ISSUE 033Buyer Brief
Why are my VSC and check-engine lights on together?
VSC and check-engine lights can appear together without proving one shared failure. Learn which indicator is on, what a regular OBD scan can read, and the next exact check.
ISSUE 032Buyer Brief
Why is my airbag light on, and what should I do?
An airbag or SRS warning means the restraint system detected a problem that needs exact vehicle guidance and prompt inspection. Learn what the light proves, why an engine scan may miss it, and what to preserve before service.
ISSUE 031Buyer Brief
Why is my ABS light on if the brakes feel normal?
Normal pedal feel does not prove ABS is working or the car is safe. Check for a red brake warning or changed braking first, then read the exact ABS module.
ISSUE 030Buyer Brief
Why did my check-engine light turn off by itself?
Yes—scan it before clearing anything. The light can go out while stored, pending, permanent, or readiness evidence remains. See what to check next.
ISSUE 029Buyer Brief
Can a loose gas cap cause a check-engine light?
Yes. A loose or damaged gas cap can trigger an EVAP-related check-engine light—but tightening it does not prove the fault is fixed or the car is inspection-ready.
ISSUE 028Buyer Brief
A used EV needs more than a charge percentage
A buyer evidence checklist spanning low-voltage behavior, charging, faults, thermal context, history gaps, and independent inspection.
ISSUE 027Case Debrief
EV repair verification needs the same proving condition
Why before and after evidence should match temperature, charge state, load, event timing, and data source.
ISSUE 026EV Brief
An EV flight recorder does not need a location trail
How bounded signal capture, owner consent, event markers, local processing, and signed summaries can preserve diagnostic value.
ISSUE 025EV Brief
A charging fault can belong to the car, station, cable, or grid
A structured way to separate vehicle, connector, supply, thermal, authorization, and charging-network causes.
ISSUE 024EV Brief
Temperature belongs in every EV range conclusion
Why ambient conditions, pack temperature, cabin demand, preconditioning, speed, and route load change usable energy evidence.
ISSUE 023EV Brief
Cell imbalance needs temperature, load, and repeat evidence
How voltage spread can guide the next battery test without declaring a failed module from one snapshot.
ISSUE 022EV Brief
EV state of charge is not battery health
Why a dashboard percentage cannot establish capacity, balance, resistance, degradation, or remaining battery life.
ISSUE 021EV Brief
Connected-vehicle data should begin and end with the owner
A privacy and evidence boundary for owner authorization, minimum scopes, revocation, deletion, and read-only vehicle data.
ISSUE 020Access Truth
A secure gateway is an authorization boundary, not a bug
Why legitimate OEM access, identity, subscriptions, audit trails, function scope, and revocation are part of modern diagnostics.
ISSUE 019Case Debrief
Stable vehicle voltage is part of the diagnostic session
Why key-on load, battery condition, chargers, long scans, service functions, and programming risk require explicit power evidence.
ISSUE 018Access Truth
Why won't my OBD2 scanner connect to my car?
Use the free connection-stage checker to separate adapter power, phone access, adapter handshake, vehicle response, and module coverage before retrying.
ISSUE 017Buyer Brief
Capture freeze frame before the clear command removes context
Why load, RPM, temperature, speed, fuel state, and supported snapshot fields can be more useful than the code label alone.
ISSUE 016Access Truth
DoIP is an Ethernet path, not an automatic OEM session
What vehicle discovery, routing activation, addressing, timing, TLS variants, authorization, and exact profiles add to Diagnostics over Internet Protocol.
ISSUE 015Access Truth
J1939 heavy-duty support starts with address discipline
How source addresses, parameter groups, DM1 and DM2 reads, transport limits, connectors, and operator confirmation shape a safe truck workflow.
ISSUE 014Access Truth
Older OBD-II vehicles need more than a modern CAN assumption
Why K-Line, ISO 9141, KWP2000, SAE J1850, initialization behavior, and adapter electronics still matter for legacy coverage.
ISSUE 013Access Truth
Laptop or phone: choose the diagnostic surface by the job
A practical comparison of portability, session length, adapter transport, report work, privacy mode, and evidence handoff.
ISSUE 012Access Truth
A CAN FD label does not prove diagnostic compatibility
The controller, transceiver, firmware, framing, timing, transport, driver, and vehicle evidence required before a CAN FD adapter claim is useful.
ISSUE 011Case Debrief
Mode 06 can show test evidence without naming the failed part
How onboard monitor results, limits, test identity, operating conditions, and manufacturer context should shape the next diagnostic step.
ISSUE 010Buyer Brief
Why a permanent DTC can remain after codes are cleared
How stored, pending, and permanent code states differ, and why a scan tool cannot simply erase every emissions record.
ISSUE 009Access Truth
Can a regular OBD2 scanner read ABS and airbag codes?
Usually not through generic OBD2. ABS, airbag/SRS, and stability-control codes require exact manufacturer-enhanced module access, definitions, hardware, and authorization.
ISSUE 008Access Truth
BLE and Bluetooth Classic are not interchangeable OBD-II paths
Why adapter radio type, operating-system policy, service layout, and firmware behavior must match before vehicle communication begins.
ISSUE 007Access Truth
Can you use an OBD2 scanner with a Mac?
Yes—when the adapter and its Bluetooth, USB, serial, or Wi-Fi connection are supported. A Mac improves the workspace; it does not create vehicle or module coverage.
ISSUE 006Fleet Evidence
What changed after return—and what the scan cannot accuse
A neutral evidence model for fleets, rental operators, and high-value vehicle custody.
ISSUE 005Parts Desk
The part number has to survive the marketplace
A RockAuto-first identity workflow that compares price only after brand, manufacturer number, suffix, and position match.
ISSUE 004EV Brief
The small battery can make an EV look catastrophically broken
How low-voltage wake-up behavior can create broad EV warnings without proving a traction-battery failure.
ISSUE 003Access Truth
What “all systems support” would actually have to mean
The hardware, software, authority, vehicle, module, and function dependencies hidden inside one marketing phrase.
ISSUE 002Case Debrief
How one P0171 can become $690 in unnecessary parts
A lean-code case debrief about operating state, fuel correction, and the first test that actually separates causes.
ISSUE 001Buyer Brief
The clean scan that had not tested itself yet
Why zero codes and incomplete readiness are two different facts in a used-vehicle inspection.
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No content mill. Every scheduled issue must pass scope, duplicate-intent, claim, source, safety, internal-link, accessibility, representation, and conversion checks before entering the runway.
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