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Mobile & Roadside Service
The mobile mechanic's certification.
6 skill areas
60 key concepts
$0 to learn
Mobile & Roadside Service is unique to Mechanicrank — no other certification body has an official mobile-work credential. Covers the operational, safety, and diagnostic considerations that differ from shop work. Everything below is free — no login, no paywall. Work through the skill areas, drill them in Study Mode, and when you're ready, prove it with the certification exam.
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Your readiness to certify
Drill all 60 concepts in Study Mode. Mark each one “Got it” once you know it cold. When every concept is cleared, you're ready for the MOB exam.
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What you'll be able to do
- Mobile diagnostic toolkit essentials
- Roadside safety protocols and traffic control
- Portable lift and jack safety
- Efficient parts sourcing on-the-fly
- Battery, alternator, and starter swap procedures at the customer's location
- Common roadside repairs: brakes, hoses, belts, jump starts, lockouts
- When to complete on-site vs. tow to shop
- Customer communication and mobile-work billing practices
Skill areas
Jump to any area — each one distills the concepts you need to master it.
Safety
8 concepts- Chocks on the downhill side prevent the vehicle from rolling further downhill if the jack fails. On an incline, you should NEVER trust the parking brake alone, and moving the vehicle isn't always practical.
- Two jack stands on manufacturer-rated jack points is the minimum for safe undercar work. The jack itself is NEVER a safety device — always use jack stands. Placement should always match the vehicle's structural jack points.
- Creating a visible work perimeter with cones prevents other vehicles and pedestrians from entering your workspace. This protects both you and them, and it's a professional standard that also serves as visual signage that you're working.
- Leaning jack stands are a fatal accident waiting to happen. There is no scenario in which continuing work is acceptable. Exit, correct, and re-verify placement before continuing.
- Children near working vehicles are a safety catastrophe. The professional immediately stops, involves the parent respectfully, and doesn't resume until the situation is safe. Never work around unsupervised children.
- The most common breaker bar injury is a slipped fastener causing the bar to swing through the operator's hand or face. Body position — never in the swing path — is the primary defense. Gloves help with grip but don't prevent this.
- Whenever you're inside the engine bay, physically remove the key/keyfob and keep it in your possession. Verbal instructions to customers get forgotten. This has prevented countless serious injuries.
- Disconnecting the battery prevents welding current from damaging vehicle electronics. Covering fuel components with a fire blanket prevents ignition. Both are non-negotiable before hot work on a vehicle.
Tools
5 concepts- A bench-mounted hydraulic press cannot practically be brought to a job site. All the other tools are portable and essential for mobile diagnostic work.
- Low-profile floor jacks fit under lowered vehicles and typically lift 2-3 tons, while scissor jacks (the type included with vehicles) are for emergency tire changes only and struggle with lowered vehicles or heavier applications.
- At highway breakdowns, warning devices placed 100-300 feet before the vehicle give oncoming traffic time to move over or slow down. Nothing else is more important than scene visibility.
- A high-capacity portable inverter connected to your work vehicle gives you 110V power without depending on the customer's home or dragging cords. It works on highway calls, parking lots, and homes without accessible outlets.
- Solo mobile mechanics can't practically transport 2-post or 4-post lifts. Low-profile floor jacks + proper jack stands handle 95% of work. Ramps are helpful for oil changes only. Portable lifts exist but are expensive and heavy.
Diagnostics
13 concepts- An OBD-II scanner will show stored codes, live data (fuel pressure sensor, RPM, cam/crank correlation), and freeze frame data — quickly narrowing whether it's fuel, spark, or timing related without further disassembly.
- Intermittent electrical faults require capturing data during the failure event. A logger or freeze-frame gives you evidence, not guesses. Parts-swapping is expensive and doesn't confirm the actual cause.
- Intermittent problems require duplication or logging. A professional explains this to the customer and offers a systematic approach — either a data logger over several days or arranging to be present when the fault occurs. Never sell parts as guesses.
- Bidirectional control lets you command a fuel pump, injector, cooling fan, or ABS actuator directly — proving whether the component works before ordering parts. This is often the difference between diagnosing correctly and guessing.
- P0420 can be triggered by faulty O2 sensors, exhaust leaks, engine misfires, or fuel system issues — not just a bad catalyst. Selling a $600+ cat replacement without ruling out the cheaper causes damages your credibility when the light returns.
- A fuel pressure gauge attached at the schrader valve or in-line gives you a direct pressure reading. While scan tools display fuel pressure sensor data on newer vehicles, mechanical verification is more reliable, especially when sensors themselves may be faulty.
- Triggered logging with pre-trigger buffer captures conditions leading up to and during the failure — the key diagnostic data. Constant logging fills storage; post-fault logging misses the failure moment.
- Voltage drop across a cable under load should typically be under 0.2V. 0.6V of drop indicates poor connections or degraded cable — often the root cause of intermittent starting or charging issues that get misdiagnosed as bad batteries or alternators.
- Freeze frame data (RPM, load, coolant temp, throttle position at the time the code set) tells you when the misfire occurred. Duplicating those conditions during testing helps you catch the misfire live and identify the failing cylinder.
- A single cylinder that's low tells you it's a specific-cylinder problem, but you still need to narrow WHY — is it fuel (injector), spark (coil/plug), or mechanical (compression)? Compression testing quickly rules out mechanical causes.
- A test light shows presence of power but not quality — a wire with high resistance may light a test light but not deliver adequate voltage under load. A DMM shows the actual voltage. If the component draws current, back-probe the connector under load.
- Vacuum leaks are the number one cause of lean codes on gasoline engines. Unmetered air enters after the MAF sensor, so the ECU doesn't know how much extra air is present and can't add enough fuel to compensate. Always smoke test or check intake vacuum before replacing parts.
- A mechanical stethoscope (or long screwdriver as an ear) at the injector body reveals whether the injector is receiving pulses. No click = no signal or no injector operation. Fastest non-invasive test.
Roadside Repairs
14 concepts- Check for signs of a damaged battery (leaking, swelling, obvious corrosion) BEFORE connecting a jump pack. A physically damaged battery can rupture or explode when current is applied.
- Connecting the final negative to an engine ground point (not the battery) prevents sparks from occurring near the battery, which may be venting hydrogen gas. This is a safety-critical procedural detail.
- Before opening any vehicle, verify ownership (registration, ID matching). Aiding vehicle theft — even unintentionally — is a serious legal exposure. Most mobile mechanics who do lockouts have a documented verification process.
- Overheating causes engine damage. Simply refilling coolant without knowing WHY it lost coolant may send the customer down the road to catastrophic engine failure or a fire. Diagnose the root cause first, then decide.
- Front brake pads are a fast, well-scoped job requiring only lift equipment and basic tools. Major internal work (transmission, head gasket) requires shop conditions. Frame welding requires more preparation than typical roadside work.
- A weak battery or high resistance in the charging circuit can mimic a bad alternator. Confirming battery health and testing voltage drop between alternator and battery ensures you're replacing the actual failed component.
- Hot coolant scald injuries are common and severe. Waiting for cooling and proper drain protects both you and the vehicle. Stop-leak and tape are not repairs — they're delays.
- At highway breakdowns, being struck by traffic is the number one hazard. Setting up warning devices and putting on high-vis gear takes 60 seconds and prevents catastrophic outcomes.
- You're not obligated to work in dangerous conditions. Recommend towing to a safer location — a well-lit parking lot, gas station, or the customer's home — and dispatch there. Insurance often covers tows in these situations.
- Never run a vehicle inside a closed garage — CO poisoning can develop rapidly. If jumped and started, open the garage door immediately and back the vehicle out before doing any diagnostic idling.
- Lug nuts torqued unevenly can warp brake rotors, damage wheel studs, or come loose. Always use a torque wrench and follow a star (cross) pattern to seat the wheel evenly. This is one of the most-missed steps on hurried roadside calls.
- Verifying charging voltage at the battery with loads applied (headlights, blower on high, defroster) confirms the alternator is delivering under real-world conditions. Charging light off doesn't guarantee proper output.
- Bad cables cause repeat starter failures. Testing voltage drop on both positive and ground paths before installing a new starter catches degraded cables — otherwise the new starter fails prematurely from voltage starvation.
- Once the radiator is damaged, coolant containment is unreliable. Replacing just the belt sends the customer down the road to overheating and potentially catastrophic engine damage. Tow to shop for proper radiator diagnosis is the professional call.
Business
18 concepts- Ranges with a waived-on-completion diagnostic fee are the industry standard for mobile work — protects your time if the customer declines, but doesn't cost them anything if they proceed.
- Understand the concern first — many disputes are misunderstandings. Documenting what was said (in writing, or a text follow-up) protects you if they later dispute in small claims or a chargeback.
- A signed authorization protects you if the customer disputes the scope or price afterward. Some states legally require this (like California's BAR requirements). Even where not required, it's basic protection.
- Customer-supplied parts are a business decision — some mechanics accept them, some don't. If accepted, get written acknowledgment that warranty on the part is with the customer, not you. This protects both parties.
- Card payments settle immediately and can't bounce. For mobile work where you're leaving the customer's location, this eliminates the risk of a customer stopping payment or a check bouncing after you're gone.
- A single, thoughtful follow-up feels personal. Aggressive marketing feels like spam and makes customers switch to a competitor. The professional standard is one clean follow-up and then trust that they'll call when needed.
- Never expand scope without authorization. This is the number one cause of customer disputes and Yelp complaints in the industry. Stop, explain, quote, get approval — even if it means an inconvenient callback later.
- Informal credit is where mobile businesses die. Even good customers forget or delay. Professional processors like Klarna, Affirm, or Square Financing let you extend credit while getting paid immediately.
- Personal auto policies typically EXCLUDE commercial use. If you have an accident while using your vehicle for work, your claim may be denied. Commercial auto insurance or a rider is essential. This is a common but severe gap for new mobile mechanics.
- General liability covers third-party property damage — the customer's car, driveway, garage, or belongings you damage while working. It does NOT cover your own tools (need Tools & Equipment coverage), your vehicle (auto insurance), or your own injuries (health/workers comp).
- Garage Keepers coverage protects you when a customer's vehicle is damaged while under your control — even by fire, theft, or vandalism. For mobile mechanics who leave a vehicle overnight or take it briefly for test drives, this is important coverage.
- California BAR registration is required for all auto repair (including mobile), written estimates are required for work above threshold amounts, and unauthorized additional charges above the estimate are illegal. Most states have similar consumer protection frameworks.
- Effective hourly rate reveals the truth: are you actually making money after all the unbilled drive time, parts runs, and quotes? Many mobile mechanics discover they're effectively earning $25/hr after tracking this — a wake-up call to raise rates or restructure.
- Silent customers are often either scheduling problems (they forgot) or ghosts (they hired someone else). A multi-channel confirmation attempt clarifies. Showing up without confirmation risks wasting a slot; canceling too fast loses good customers who simply missed a call.
- Under most state consumer protection laws (including California BAR), text or email approval of a written estimate is treated as valid written authorization. Keep the estimate + text response as your record.
- 12 months or 12,000 miles is the industry standard for both parts and labor. Parts often come with their own manufacturer warranty. Setting expectations up front (in the invoice) prevents disputes later.
- Off-book work skips liability insurance, invoicing, and authorization. It's also uninsured — if you damage the vehicle you have no protection. Professional response: offer to schedule properly.
- For most solo mobile mechanics, the bottleneck is time spent on phones and scheduling — non-billable hours. A dispatcher/scheduler at $15-20/hr can create 15-20 additional billable hours per week for you at your $100+/hr rate. Highest ROI first hire.
Parts Sourcing
2 concepts- Late-night mobile calls require parts NOW. Building relationships with 24-hour parts stores and knowing which have your customer's belt/hose/battery in stock is core mobile business infrastructure.
- Standard mobile mechanic parts markup is 15-40% depending on the part. It covers pickup time (which you don't bill hourly for during a parts run) and warranty exposure. Customer-supplied parts create warranty problems and should generally be discouraged.
READY TO PROVE IT?
Studied the material? Get MOB certified.
The Mobile & Roadside Service exam turns what you just learned into a verifiable credential drivers and shops can look up. 45 questions · 60 minutes · 75% to pass · $19.99.
Studying here is free forever. There's no obligation to take the exam.