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Preventive Maintenance & Inspection
Oil, filters, fluids, safety inspection — done right.
7 skill areas
60 key concepts
$0 to learn
Preventive Maintenance & Inspection is the foundation service every mechanic performs. Includes proper multi-point inspection methodology and pre-purchase inspection standards. 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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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 PMI exam.
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What you'll be able to do
- Oil change procedures across major platforms (including oil filter housing variants)
- Fluid services: transmission, differential, transfer case, brake, coolant
- Air and cabin filter service
- Belts, hoses, and pulley inspection
- Battery load testing and inspection
- Multi-point inspection methodology
- Pre-purchase inspection standards (35-125 point PPI)
- Customer reporting: what to recommend, what to defer, what to prioritize
Skill areas
Jump to any area — each one distills the concepts you need to master it.
Oil Service
8 concepts- Using a full synthetic of the correct viscosity is always safe and often extends service intervals. The concern of switching to synthetic causing 'leaks' is a myth — modern oils are compatible. The only rule: match the manufacturer's specified viscosity.
- Lubricating the gasket allows it to seat properly without twisting or tearing. Overtightening damages the gasket and makes future removal difficult. The 3/4 to 1 turn spec (or manufacturer torque) prevents both leaks and overtightening.
- The housing O-ring (or gasket, depending on design) is the primary seal. It ships new with every cartridge filter kit but is often reused, leading to slow leaks 500 miles later. Always replace it.
- Dark oil is normal — it means the oil is doing its job absorbing combustion byproducts. Warning signs are: milky (coolant), gasoline smell (fuel dilution), or visible metal. Color alone doesn't indicate emergency.
- Modern aluminum oil pans strip easily if drain plugs are overtightened. Manufacturer torque specs (typically 20-30 ft-lbs) prevent this. Overtightening creates a leak that requires oil pan replacement — an expensive repair caused by a $2 oil change.
- Missing 2 quarts is significant. Investigate: external leaks first (visible drips, wet valve covers), then PCV system, then potential internal (valve seals, rings). Track consumption rate. Some engines burn oil normally — Subaru, older BMW inline-6, etc. — but this warrants documentation.
- 20% is low — approaching required service. After changing oil, reset the oil life monitor. Failing to reset means the customer's next reminder is off, potentially leading to skipped services later. Reset procedures vary by manufacturer — some require button sequences, others need a scan tool.
- European manufacturers specify approved oil standards. Using off-spec oil can cause turbo damage, timing chain wear, sludge, and warranty voids. Always confirm the specific standard for the vehicle — 'synthetic 5W-30' is not enough.
Fluid Services
11 concepts- Fresh ATF (automatic transmission fluid) is red or pink. Very dark brown or black fluid indicates overheating and severe degradation. The transmission has already suffered heat damage — recommend a service AND thorough inspection.
- CVT fluid is engineered for the belt/chain and pulley system in CVTs. Using standard ATF causes the belt to slip and can destroy the transmission within thousands of miles. Always use the exact manufacturer-specified fluid.
- Manual transmissions have a drain plug at the bottom and a fill plug on the side — the fill plug height determines the correct fluid level. Fill until fluid seeps out level, then reinstall the fill plug. There's no dipstick.
- 50/50 coolant-to-distilled-water provides the optimal balance of freeze protection, boiling point, corrosion inhibition, and heat transfer. Tap water contains minerals that cause scale buildup. Pure coolant has worse heat transfer than the mix.
- Brake fluid is hygroscopic — it absorbs water from the atmosphere. Water lowers the boiling point of the fluid. When brakes get hot, the water flashes to steam causing brake fade. Testing reveals when a flush is needed regardless of color.
- The industry standard for brake fluid flush is 2% moisture content or higher. At 3.5%, the boiling point is severely compromised and brake fade risk is elevated. A full flush is warranted.
- Systematic bleeding at each caliper — starting furthest from the master cylinder (typically RR, LR, RF, LF for most cars) — ensures all air is displaced. Simply pumping the pedal doesn't remove air trapped in the system. Some vehicles now require scan-tool-controlled ABS bleeding after fluid service.
- Foamy power steering fluid indicates air is entering the system. Common causes: low fluid level, worn pump seals, cracked return hose, or old fluid. Fresh fluid should be pinkish-red (or clear, depending on brand) and free of foam.
- Coolant chemistries (IAT green, OAT orange/dex-cool, HOAT yellow, etc.) can react with each other, forming gel that blocks cooling passages. Always drain, flush, and refill with the manufacturer's specified chemistry. Universal coolants exist but must be applied per manufacturer approval.
- Common ATF service mistakes: (1) not draining the torque converter leaves most of the old fluid inside, (2) overfilling causes foam and shift issues, (3) overtightening the pan bolts strips threads. A proper service addresses all three.
- Fine glitter-like particles in differential fluid are normal from gear-on-gear wear. Larger chunks, chips, or excessive particles indicate damage. Small glitter alone with normal fluid color is not an emergency.
Multi-Point Inspection
20 concepts- A tiered inspection report communicates severity clearly. 'Immediate Safety' items require action before driving, 'Recommended Now' items should be addressed within days/weeks, and 'Watch' items are being monitored. This builds trust and reduces upsell perception.
- A torn CV boot means the grease is escaping and contamination is entering the CV joint. The joint may run for months but is deteriorating. Replacing the boot (or the axle if damaged) now is far cheaper than the CV/axle replacement it will require if ignored.
- New pads are typically 10-12mm. Wear threshold is ~2-3mm. At 4-5mm the pads are used but not immediately dangerous. Recommend within the next few thousand miles or before the next service, but no emergency.
- The legal minimum is 2/32" but wet-braking performance degrades drastically below 4/32". At 3/32", the customer is approaching a serious safety issue and should replace before winter or the wet season.
- Rear main seals require transmission removal on most vehicles (major labor). If the leak is minor and only marking the driveway, monitoring may be more cost-effective than repair. If the leak is significant enough to affect oil level, address it. Discuss the tradeoffs honestly with the customer.
- Small amounts of fine metal (like glitter) are normal in differential fluid. Larger metallic particles or chunks indicate gear/bearing damage. Servicing the fluid without inspection won't fix the underlying wear. Recommend a full diff inspection.
- Replacing shocks/struts in pairs (front axle or rear axle) maintains balanced handling. Mixing new and old on the same axle causes uneven ride and handling problems. This is the industry standard even when only one component appears failed.
- Parking brake failure is a safety issue. It's the redundant hold when the transmission fails or park pawl breaks. Also required for state safety inspections. Immediate service is warranted.
- Exhaust rust is normal and doesn't require action until it causes leaks or structural issues. Recommending replacement based on cosmetic rust erodes customer trust and appears predatory.
- Wheel bearing failure at highway speed is dangerous — potential wheel lockup or complete separation. Slight play indicates near-term failure. Recommend replacement within weeks, not months.
- Honesty builds long-term trust. A customer who receives an honest 'everything looks good' report will return for years. Manufactured findings destroy trust the moment they suspect (or worse, catch) the pattern.
- Deep grooves consume material below serviceable thickness. Heat spots indicate crystallized metal that will crack. Modern rotors are also thinner than they used to be — resurfacing often takes them below minimum. Replacement is usually the correct call.
- Ball joints connect suspension components. Complete failure (which follows visible play) drops the wheel angle catastrophically and can cause total loss of control. This is one of the highest-priority safety findings in an inspection.
- Feathered/scalloped edge wear indicates alignment problems. Inside-edge wear typically indicates toe-out. Simply replacing tires without correcting alignment will cause the new tires to wear the same way. Always inspect and quote alignment with tire recommendations.
- New plug electrodes are sharp-edged. Wear rounds the electrode, increasing the gap and voltage requirement. Eventually the ignition system can't jump the gap under load, causing misfires. Replace at manufacturer interval (60-100k on iridium/platinum plugs).
- Torn motor mounts allow the engine to shift under acceleration, potentially damaging attached hoses, wiring harnesses, and drivetrain components. Not immediate safety, but a real issue that will cause cascading failures if unaddressed.
- Headlight bulbs age together. If one is out, the other is close to failure. Recommending pair replacement saves the customer a return trip and possibly a state inspection failure. It's not upselling — it's practical maintenance.
- The intake tube is downstream of the MAF sensor — any air entering through cracks is unmetered. The ECU doesn't know about it, can't add fuel to compensate, and lean codes result. Cracked intake tubes are a common cause of P0171/P0174 codes.
- Cabin air filters clean the air passengers breathe. A moldy filter blows contaminated air into the cabin every time the HVAC runs. This can trigger allergic reactions, worsen asthma, and cause chronic exposure to airborne mold. Address as a health priority, not just cosmetic.
- Written, photographic documentation is now the industry standard for inspections. It builds trust, provides value the customer can reference later, and protects you legally if disputes arise. Even for jobs where they decline further work, the documentation reinforces your professionalism.
Belts and Hoses
6 concepts- Visual inspection: perpendicular cracks in the ribs, missing rubber chunks, glossy/glazed surface, or fraying edges all indicate replacement. Age or mileage exceeding the manufacturer's spec is also an indicator even if the belt looks OK visually.
- Timing belt intervals are safety-critical. On interference engines (most modern engines), belt failure causes pistons to strike open valves, destroying the engine. The cost of replacement ($800-1500) versus rebuild ($4000-8000+) is not comparable.
- The water pump is often driven by the timing belt and is behind the same components you're already removing. Skipping the water pump means doing all the labor twice when it fails at 130k miles. Combined service is always recommended.
- Squeeze test: healthy hose feels firm. Sponge-soft indicates deterioration from the inside; brittle indicates dry rot; soft spots or bulges are pre-failure warning signs. This test catches most hose failures before catastrophic rupture.
- Serpentine belt tensioners have sealed bearings. A squeaking tensioner is a failing bearing — imminent seizure or shaft failure. Replace the tensioner AND the belt together (belt will show additional wear from the failing tensioner) for a complete repair.
- Belt routing is critical — reversed routing causes water pump to run backwards, alternator failure, or immediate belt shedding. Photograph BEFORE removal, then verify against service data. Many engines have routing stickers under the hood as a reference.
Air Filters
3 concepts- Air filters are meant to trap dirt — dark color is normal. Replacement is warranted when visibly clogged (light won't pass through), damaged, or at the manufacturer's interval. Some vehicles now have 30k+ mile intervals with modern paper filters.
- Cabin air filters are separate from engine air filters and clean the air the driver/passengers breathe. Neglected cabin filters cause reduced HVAC airflow, musty smells, and mold. Recommend annual replacement or at manufacturer interval.
- The air filter gasket seals the airway. If it's degraded, unfiltered air bypasses the filter — potentially damaging the MAF sensor and letting debris into the engine. Filter media condition alone doesn't matter if the seal fails. Replace the filter.
Battery
6 concepts- Under load test, a healthy 12V battery should maintain at least 9.6V. Anything below indicates internal cell degradation and imminent failure. Replacement is warranted regardless of age.
- Heavy corrosion can indicate case cracking or internal degradation. Clean, protect, and monitor closely. Note in the inspection report that battery replacement is likely needed within 6 months even though it currently tests OK.
- Battery life in hot climates (AZ, TX, southern CA) is typically 3 years vs. 5+ in moderate climates. A marginal test at 3 years in Arizona means near-term failure. Preventive replacement saves the customer a stranded call and no-start emergency.
- AGM batteries have different internal characteristics — a conventional carbon-pile load tester or high-amp draw can damage them. Modern smart testers (Midtronics, etc.) have AGM/EFB/flooded settings that apply the correct test methodology.
- Start/stop systems cycle the battery hundreds of times per day. Flooded batteries cannot handle this and will fail rapidly. AGM (or EFB) batteries are specifically designed for start/stop. Also, the BCM (battery control module) may need reset/coding for the new battery.
- 12.6-12.8V is a fully charged battery at rest. 12.4V is roughly 75% charged. 12.2V is 50%. Below 12.0V is significantly discharged and cycling. Consistently low resting voltage suggests parasitic drain or charging system issues.
Pre-Purchase Inspection
6 concepts- PPI reports should be thorough, honest, and documented. Photos + repair estimates + severity rating give the customer real negotiation leverage. The inspection's value is the actionable information.
- Frame damage on a modern unibody vehicle is a major concern — it affects crash safety, alignment, and resale value. The PPI report should clearly flag this as a fundamental issue, not a routine repair item.
- Diesel-specific PPI items include emissions delete evidence (which is illegal and requires expensive re-installation), fuel injector rate testing, glow plug function, and turbocharger inspection. Diesel repair costs 2-3x gasoline, so the PPI matters more.
- The battery pack is the most expensive component on an EV and its state-of-health determines the vehicle's remaining useful life. A scan tool that reads battery health (percentage of original capacity) is essential for EV PPI. Without this, the customer is buying blind.
- Rebuilt (salvage) titles significantly reduce vehicle value (often 20-40%) and may hide undisclosed damage. The PPI report should prominently note this so the customer negotiates accordingly. It's not automatic disqualification — some rebuilds are quality — but transparency is essential.
- Sellers sometimes clear codes right before selling to hide check engine lights. Readiness monitor status reveals this — unset monitors mean codes were recently cleared and haven't had time to re-set. Modern PPIs must include this check.
READY TO PROVE IT?
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