CONOCER Mantenimiento Mecánico Automotriz (EC1121, Mexico)

A technician prepares to measure battery open-circuit voltage during a diagnostic inspection. Which multimeter function and range selection must be chosen to obtain an accurate reading on a standard 12-volt automotive electrical system?

• ADirect Current Volts (DCV) set to the 20V range or auto-ranging DC
• BAlternating Current Volts (ACV) set to the 200V range
• CDirect Current Amperes (DCA) with the red lead in the 10A jack
• DResistance (Ohms) set to the 2k range

During engine cranking, a technician performs a voltage drop test on the positive battery cable from the battery positive terminal post to the starter solenoid B+ terminal. The digital multimeter records a reading of 0.65 V. How should the technician evaluate this result?

• AExcessive drop: high resistance in the cable or its connections that must be repaired
• BNormal voltage drop is present, since starter circuits routinely drop between 0.50 V and…
• CThe positive cable is completely open-circuited, requiring immediate battery replacement
• DThe starter motor internal armature windings have shorted directly to the engine ground

EC1121 Element 1 expects the technician to prepare the work area wearing a uniform and personal protective equipment (equipo de protección personal, EPP). Under Mexico's current PPE standard, NOM-017-STPS-2024, how is the specific EPP for a workshop task determined?

• AThe employer analyzes the task's risks, then determines, provides, and trains workers on…
• BEC1121 publishes one fixed EPP list that every certified mechanic must wear for every task
• CEach technician chooses EPP by personal preference, and the employer supplies it only if…
• DEPP is required only when handling chemicals; mechanical work under a lifted vehicle need…

Under CONOCER EC1121 Element 2 (Realizar el mantenimiento del vehículo), which set of actions makes up the first performance criterion, preparing the vehicle for maintenance?

• AVerify existing covers, add those the repair needs, list parts on the requisition, prepar…
• BBegin the maintenance immediately and complete the parts requisition afterward from the f…
• CRemove the covers fitted at reception so they do not get in the way, then protect only th…
• DPosition the vehicle and prepare tools; immobilizing the vehicle is required only when it…

What is the standard form and usual location of the OBD-II Data Link Connector (DLC) on light passenger vehicles?

• AA 16-pin D-shaped connector in the cabin, usually under the driver's side of the dash
• BA 12-pin circular connector located inside the trunk near the spare tire compartment
• CAn 8-pin square connector mounted directly on top of the air cleaner assembly in the engi…
• DA 24-pin rectangular connector integrated into the instrument cluster behind the speedome…

A diagnostic scan tool retrieves code P0302 from the powertrain control module. What does this standardized diagnostic trouble code (DTC) indicate?

• APowertrain fault, SAE generic definition, ignition system/misfire detected on cylinder nu…
• BChassis fault, manufacturer proprietary definition, wheel speed sensor error on the left…
• CBody fault, SAE generic definition, open circuit in the passenger side airbag deployment…
• DNetwork communication fault, CAN bus data lost from the electronic transmission controller

When examining OBD-II freeze frame data on a scan tool after a malfunction indicator lamp (MIL) illuminates, what specific information does this data deliver to the technician?

• AA snapshot of engine data such as RPM, coolant temperature, speed, load, and fuel trims s…
• BA list of every trouble code the vehicle has stored since new, including codes that were…
• CA continuous log of all sensor data for the entire trip during which the fault occurred
• DThe manufacturer's recommended repair procedure for the stored code

A vehicle displays a Check Engine light with code P0171 (System Too Lean, Bank 1). While reviewing live data at idle, the technician observes Short-Term Fuel Trim (STFT) at +19% and Long-Term Fuel Trim (LTFT) at +22%. What do these fuel trim readings signify?

• AThe ECM is adding fuel to correct a lean condition such as unmetered air or low fuel deli…
• BThe engine control module is reducing fuel injection volume because the engine is running…
• CBoth oxygen sensors have completely shorted to ground and are reporting invalid zero-bias…
• DThe fuel pressure regulator has failed completely open, delivering excessive fuel rail pr…

A technician conducts a cylinder compression test on a four-cylinder engine. Cylinder 1 produces 160 psi, Cylinder 2 produces 155 psi, Cylinder 3 produces 95 psi, and Cylinder 4 produces 160 psi. Adding a tablespoon of clean motor oil into Cylinder 3 raises its compression to 145 psi. What mechanical defect is diagnosed?

• AWorn or stuck piston rings in Cylinder 3
• BA burned or poorly seating exhaust valve in Cylinder 3
• CA cracked intake manifold runner feeding Cylinder 3
• DA blown cylinder head gasket between Cylinders 1 and 2

During a cylinder leakage test with the cylinder positioned at top dead center (TDC) on its compression stroke and compressed air applied at 100 psi, the technician hears air hissing loudly out of the vehicle throttle body. What does this observation verify?

• AThe intake valve for that cylinder is leaking or improperly seated
• BThe exhaust valve face has burned away or failed to close
• CThe cylinder head gasket has breached into an adjacent water jacket
• DThe engine oil dipstick tube O-ring seal has deteriorated

A vacuum gauge connected to a direct intake manifold port on an engine running at warm curb idle displays a steady reading of 19 inches of mercury (in-Hg). How should this measurement be interpreted?

• ANormal engine mechanical condition with healthy manifold vacuum and proper sealing
• BSevere restriction in the exhaust system or a completely plugged catalytic converter
• CLate ignition timing or significantly retarded camshaft valve timing
• DWorn piston rings permitting massive blow-by into the intake plenum

Where should a mechanical fuel pressure test gauge be connected when evaluating the fuel delivery system on a port fuel-injected (PFI) gasoline engine?

• ATo the Schrader test valve fitting located directly on the fuel delivery rail
• BTo the intake manifold vacuum port that supplies the fuel pressure regulator's reference…
• CDirectly into the fuel vapor purge line leading to the EVAP canister
• DTapped into the power steering high-pressure hydraulic circuit

A fuel pressure gauge connected to a vehicle fuel rail reads 45 psi with the engine running. Immediately after turning off the ignition, fuel pressure drops rapidly to 5 psi within 20 seconds. What is the most probable cause of this rapid pressure loss?

• AA leaking injector, a failed pump check valve, or a leaking pressure regulator
• BA completely restricted in-tank fuel pickup sock filter
• CContaminated gasoline with excessive ethanol concentration
• DAn open circuit in the electric fuel pump relay control coil

When monitoring the live voltage signal of a conventional zirconia upstream oxygen sensor (O2S 1) on a warmed-up engine running in closed loop at 2,000 RPM, what behavior indicates normal operation?

• AThe voltage keeps switching between about 0.1 V and 0.9 V
• BThe voltage remains solidly locked at exactly 12.0 V direct current
• CThe voltage holds perfectly steady at 0.00 V under all throttle positions
• DThe voltage gradually increases to 5.0 V and remains permanently constant

While diagnosing a vehicle with an illuminated Check Engine light displaying catalyst efficiency code P0420, how does the signal from the downstream oxygen sensor (Sensor 2) compare to the upstream sensor (Sensor 1) on a vehicle with a healthy, functioning catalytic converter?

• ASensor 1 switches rich-lean while Sensor 2 stays fairly steady around 0.5 V to 0.7 V
• BBoth Sensor 1 and Sensor 2 switch rapidly in perfect synchronization between 0.1 V and 0.…
• CSensor 1 remains completely steady at 0.1 V, while Sensor 2 fluctuates between 0.0 V and…
• DSensor 2 holds a steady reading near 0.1 V, showing that the catalyst is consuming all of…

What critical safety and equipment protection rule must be followed whenever using a digital multimeter to measure resistance (Ohms) in an automotive electrical circuit?

• AThe circuit or component under test must be completely de-energized with power disconnect…
• BThe vehicle ignition switch must be left in the START/CRANK position throughout testing
• CThe multimeter black lead must be plugged into the high-amperage fused terminal
• DThe component must stay connected in its powered circuit with the ignition ON so the read…

A customer states that their vehicle battery goes completely dead after being parked for two days. To perform a parasitic battery drain test, how should a digital multimeter be connected to the vehicle electrical system?

• ADC amps (or mA), in series between the disconnected negative cable and the negative post
• BSet to DC Volts and connected in parallel across the positive and negative battery termin…
• CSet to AC Volts and connected in series between the alternator output post and the starte…
• DSet to Ohms and connected in parallel across the vehicle ignition switch terminals with t…

A vehicle hesitates and stumbles during hard acceleration, and live scan tool data reveals that the Mass Air Flow (MAF) sensor reports significantly lower grams per second (g/s) than expected under wide-open throttle. What is the most common cause of this condition?

• AOil, dust, or contamination coating the heated sensing element inside the MAF sensor hous…
• BA weak ignition coil that misfires under heavy load
• CA partially clogged fuel filter that starves the engine at full throttle
• DAn upstream oxygen sensor that reads falsely rich

How does the output voltage of a conventional analog Manifold Absolute Pressure (MAP) sensor behave as engine load increases from closed throttle deceleration to wide-open throttle (WOT)?

• AIt rises from about 1 V at idle or deceleration to about 4.5 V at wide-open throttle
• BVoltage decreases from 5.0 V at idle down to exactly 0.0 V at wide-open throttle
• CVoltage remains completely constant at 2.5 V while the frequency changes from 20 Hz to 20…
• DVoltage alternates continuously between +12 V and -12 V direct current

An automotive Engine Coolant Temperature (ECT) sensor utilizes a negative temperature coefficient (NTC) thermistor. How does the internal electrical resistance of this sensor change as the engine warms up from cold ambient to normal operating temperature?

• AIts electrical resistance decreases significantly as coolant temperature rises
• BIts electrical resistance increases dramatically as coolant temperature rises
• CIts resistance remains completely fixed at 1,000 ohms under all temperatures
• DIts resistance drops to zero below freezing and rises to infinity at 90°C

A technician connects a digital multimeter or lab scope to the signal wire of a traditional potentiometric Throttle Position Sensor (TPS) with the ignition on and engine off. When smoothly opening the throttle from closed to wide open, what waveform or reading indicates a defective sensor?

• AA momentary voltage dropout or sudden jagged spike to 0 V or 5 V during the sweep
• BA smooth, continuous voltage progression rising gradually from approximately 0.5 V to 4.5…
• CA total elapsed time of 2 seconds required to manually move the throttle linkage
• DA steady reference supply voltage of 5.0 V measured at the sensor input terminal

A technician performs a starter current draw test on a four-cylinder gasoline engine using an inductive clamp meter. During cranking, current draw measures 380 amperes while the engine turns over sluggishly and battery terminal voltage drops to 8.2 V. What is the most likely diagnosis?

• AHigh mechanical resistance in the engine or an internally shorted starter motor
• BExcessive high electrical resistance in the starter solenoid control circuit
• CAn open-circuited engine ground strap between the transmission and body
• DA defective ignition key tumbler switch assembly

To test the physical bus integrity and termination resistance of a standard Controller Area Network (CAN-C / High-Speed CAN) on an OBD-II compliant vehicle, where should an ohmmeter be connected and what resistance value should be measured with the vehicle battery disconnected?

• ABetween DLC Pin 6 (CAN High) and Pin 14 (CAN Low); expected resistance is 60 ohms
• BBetween DLC Pin 4 (Chassis Ground) and Pin 16 (Battery 12V+); expected resistance is 0 oh…
• CBetween DLC Pin 7 (K-Line) and Pin 15 (L-Line); expected resistance is 120 ohms
• DBetween DLC Pin 1 (Manufacturer) and Pin 9 (Manufacturer); expected resistance is 10,000…

A technician spots a fluid leak on the shop floor directly beneath the transmission bellhousing. The fluid is slippery, translucent bright red to reddish-brown, and has a petroleum aroma. What automotive fluid has leaked?

• AAutomatic Transmission Fluid (ATF)
• BEngine motor oil
• CEngine ethylene glycol coolant
• DHydraulic brake fluid (DOT 4)

During engine acceleration, thick blue-gray smoke discharges continuously from the vehicle tailpipe. What internal engine malfunction does this exhaust emission indicate?

• AEngine oil is entering the combustion chambers past worn valve stem seals or worn piston…
• BCoolant is leaking into the cylinders through a blown cylinder head gasket
• CThe fuel injection system is delivering an excessively rich air-fuel mixture
• DThe secondary air injection pump is forcing fresh atmospheric air into the catalytic conv…

Under EC1121 Element 1, after preparing the work area, the technician receives the work order (orden de trabajo). What does the standard require at this step, before the vehicle inspection begins?

• AVerify the work order, confirm it matches the vehicle, and position the vehicle in the wo…
• BStart the inspection at once; the work order is checked only when the final service order…
• CRewrite the customer's complaint in technical terms and have the customer sign the order…
• DSend the order to the parts warehouse so the parts can be requisitioned before the inspec…

A single cylinder of an engine has a cylinder displacement volume (swept volume, Vd) of 450 cubic centimeters (cc) and a combustion chamber clearance volume (Vc) of 50 cc when the piston is at top dead center. What is the calculated compression ratio of this engine?

• A10.0:1
• B9.0:1
• C8.5:1
• D11.5:1

What do the numbers and letters signify on a container of multi-grade automotive engine oil labeled SAE 5W-30?

• A5W is the cold (winter) grade and 30 is the grade at the 100°C operating temperature
• BThe first number (5W) is the viscosity grade at 100°C operating temperature, and the seco…
• CIt is a winter-only oil: the 5W grade applies below freezing, and an SAE 30 oil must be s…
• DThe 'W' stands for 'weight', and the label means the oil is a blend of 5 parts SAE 5 oil…

A customer's owner's manual for a turbocharged direct-injection gasoline car calls for an API SP oil of a stated viscosity grade. Which API service category is the newest gasoline-engine category, licensed since March 2025, that a technician can select when it also meets the specified viscosity grade and any manufacturer approval?

• AAPI SQ
• BAPI SA
• CAPI SJ
• DAPI CF

What is the correct procedure for installing a new spin-on engine oil filter during routine periodic maintenance?

• AClean the base, oil the new gasket, spin on until it touches, then hand-tighten about 3/4…
• BApply silicone RTV gasket sealant to the rubber ring, thread on, and torque tightly with…
• CInstall the filter completely dry and tighten with a metal strap wrench until the filter…
• DIf the old gasket is stuck to the mounting base, leave it in place because two gaskets se…

Which operating condition is the primary contributor to severe black sludge accumulation inside an automotive engine valve cover and oil pan?

• AFrequent short cold-weather trips, overdue oil changes, and a clogged PCV system
• BContinuous high-speed highway driving at steady engine operating temperatures
• CUsing an engine oil with an API service rating that exceeds factory minimum recommendatio…
• DReplacing the engine air filter element prematurely before the scheduled mileage limit

How should a technician inspect a mechanical spring-loaded Positive Crankcase Ventilation (PCV) valve during a minor engine tune-up service?

• ACheck that the valve rattles when shaken and that it has strong vacuum with the engine id…
• BLeave the valve in place; a PCV valve can only be judged by the oil-consumption history,…
• CPressurize the PCV valve with 150 psi of shop air in both directions to ensure bidirectio…
• DConnect a 12V battery directly to the valve body to check electromagnetic coil pull-in cu…

What is the industry-standard mixture ratio of concentrated ethylene glycol antifreeze to distilled water for most passenger vehicle cooling systems, and what thermal protection does it provide?

• A50% antifreeze and 50% water, protecting to about -37°C and raising the boiling point
• B100% pure antifreeze with 0% water, providing maximum cooling efficiency and freeze prote…
• C10% antifreeze and 90% water, formulated to prevent radiator corrosion without altering t…
• D75% antifreeze and 25% water, because every increase in antifreeze concentration always g…

A vehicle cooling system radiator cap is rated at 15 psi. During bench testing with a cooling system pressure tester, the cap relief valve releases pressure at 8 psi. What symptom will this defective cap produce on the vehicle?

• APremature coolant boilover and coolant loss into the overflow reservoir at normal operati…
• BImmediate rupture of the heater core and upper radiator hose due to excessive system pres…
• CThe engine will run permanently cold and set trouble code P0128
• DCoolant will be forced past the head gasket into the engine oil

A customer complains that the vehicle cabin heater blows only lukewarm air in winter and the engine temperature gauge barely rises above the cold mark on the highway. Diagnostic scanning retrieves code P0128. What component failure does this indicate?

• AThe engine cooling system thermostat is stuck open or opening prematurely
• BThe cooling system thermostat is stuck completely closed
• CThe engine cylinder head gasket has suffered an external oil leak
• DThe electric radiator cooling fan motor has seized mechanically

During a visual cooling system inspection, a technician discovers coolant weeping steadily from a small circular hole (weep hole) on the underside of the water pump housing. What corrective action is required?

• AReplace the entire water pump assembly, as the internal mechanical ceramic/carbon shaft s…
• BSeal the weep hole permanently using high-temperature epoxy or a threaded brass screw
• CAdd a cooling-system stop-leak additive and recheck the pump at the next scheduled service
• DTighten the water pump pulley bolts an additional two turns past factory torque specifica…

An engine overheats only when idling in traffic, but cools down to normal temperature when cruising at 80 km/h on the open highway. Which cooling system component is the most probable cause of this specific symptom?

• AAn inoperative electric radiator cooling fan or defective fan control relay
• BA missing radiator pressure cap spring
• CA completely plugged radiator core tubes
• DA defective cylinder head gasket with combustion gases leaking into coolant

What is the recommended workshop inspection method to determine if a dry paper engine air filter element requires replacement during routine vehicle maintenance?

• AShine a light through the pleats; if little light passes, replace the element
• BWash the paper element in kerosene, blow dry with 120 psi shop air, and reinstall
• CIgnore its condition and replace it only at the mileage interval, because a paper element…
• DApply a light coat of engine oil to the pleats to restore filtering efficiency, as is don…

When cleaning carbon deposits from an Electronic Throttle Control (ETC / drive-by-wire) throttle body bore, which critical precaution must a technician observe?

• AUse a cleaner safe for coated bores and don't force the motorized throttle plate open by…
• BSoak the entire electronic throttle body assembly in a bucket of concentrated carburetor…
• CScrub the bore and throttle plate with a wire brush or abrasive pad to remove the deposit…
• DDisconnect the throttle body harness and leave the battery connected while washing with w…

A technician checks the coil resistance of four port fuel injectors with a digital multimeter. Injectors 1, 2, and 4 measure 13.8 ohms, 14.1 ohms, and 13.9 ohms respectively. Injector 3 measures 1.2 ohms. What does this measurement reveal about Injector 3?

• AInjector 3 has an internal short circuit in its solenoid windings and must be replaced
• BInjector 3 is operating normally as a low-resistance high-performance unit
• CInjector 3 has an open circuit and cannot pass any electrical current
• DThe injector tip has become completely clogged with solid fuel varnish

What is the primary difference in construction and thermal operation between a 'hot' spark plug and a 'cold' spark plug?

• AA hot plug has a longer insulator nose that holds heat; a cold plug has a shorter nose th…
• BA hot spark plug generates a 50,000-volt spark, while a cold spark plug generates only 10…
• CA hot spark plug has a wider electrode gap, while a cold spark plug has a narrower gap
• DA hot spark plug is used exclusively in diesel compression-ignition engines

When adjusting the electrode gap on a set of traditional copper-core spark plugs prior to installation, which tool and technique must be employed?

• AMeasure with a wire or feeler gauge and bend only the ground electrode with the gapping t…
• BClose the gap by tapping the center electrode against the workbench until the gauge fits
• CPry against the center ceramic insulator using a flat-head screwdriver blade
• DSkip measuring, because all new copper-core plugs come pre-gapped to the correct setting…

Upon removing spark plugs from an engine that idles roughly, the technician observes that the insulator firing tips and electrodes are covered with dry, soft, velvety black soot. What does this spark plug appearance indicate?

• ACarbon fouling caused by an excessively rich air-fuel mixture, weak ignition spark, or pr…
• BOil fouling caused by leaking valve stem seals or worn piston oil control rings
• COverheating caused by severe lean air-fuel ratio or excessively advanced ignition timing
• DNormal spark plug appearance for a clean-burning vehicle meeting modern emissions standar…

When testing a two-wire Coil-on-Plug (COP) ignition coil bench resistance with a digital multimeter, what values represent normal winding conditions on a typical passenger car coil?

• APrimary about 0.5 to 1.5 ohms; secondary about 5,000 to 15,000 ohms
• BPrimary winding resistance of 0.00 ohms; secondary winding resistance of 0.00 ohms
• CPrimary winding resistance of 100,000 ohms; secondary winding resistance of 1 ohm
• DPrimary winding resistance of infinite (OL); secondary winding resistance of infinite (OL)

An engine cranks normally when the key is turned, but will not start. A scan tool displays 0 RPM during cranking, an inline spark tester shows no spark, and a noid light connected to an injector harness shows no pulse. What component failure is the primary suspect?

• ACrankshaft Position (CKP) sensor or its electrical circuit
• BVehicle Speed Sensor (VSS) mounted on the transmission output shaft
• CCamshaft Position (CMP) sensor
• DFuel pump relay

In a hydraulic brake system, the pedal linkage pushes the master cylinder piston (area 4 cm²) with a force of 400 N. A front caliper piston has an area of 24 cm². Ignoring losses, what force does that caliper piston apply?

• A2,400 N, because the same pressure (100 N/cm²) acts on the larger piston area
• B400 N, because a hydraulic system passes force through unchanged from piston to piston
• CAbout 67 N, because the force is divided by the area ratio (24 ÷ 4 = 6)
• D9,600 N, because the input force is multiplied by the caliper piston area (400 × 24)

A technician uses an outside micrometer to measure the thickness of a ventilated front brake rotor. The rotor stamp specifies 'MIN THICKNESS 22.40 mm'. The technician measures rotor thickness at four points around the friction ring, finding readings of 22.10 mm, 22.15 mm, 22.08 mm, and 22.12 mm. What action does the manufacturer's specification require?

• AReplace the brake rotor, as all measured points are below the manufacturer's minimum (dis…
• BMachine (resurface) the rotor on a brake lathe to remove an additional 0.50 mm of material
• CReinstall the rotor with new thick brake pads to compensate for rotor metal loss
• DRotate the brake rotor to the rear axle where braking forces are lower