ASE L2 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Diesel compression ignition

Diesel engines ignite fuel by injecting it into air compressed enough to reach ignition temperature; typical compression ratios are about 14:1 to 23:1.

Wet compression test

A compression test repeated after adding a small amount of oil to the cylinder; if pressure rises, worn rings are likely, while unchanged low pressure suggests valve or head leakage.

Crankcase blowby

Combustion gases escaping past rings or pistons into the crankcase; increasing blowby with load indicates worn cylinders, damaged pistons, or a failed head gasket.

Diesel white smoke

White exhaust smoke often indicates unburned fuel from low compression, retarded injection timing, or failed glow plugs; it may clear as the engine warms.

Cylinder balance test

A diagnostic test that compares each cylinder's contribution to engine speed; a weak cylinder shows a smaller speed drop when cut out and may set a misfire code.

Oil dilution by diesel

Diesel fuel entering engine oil raises the oil level and lowers viscosity; common causes are leaking injector nozzles, excessive regeneration, and incomplete combustion.

Combustion gas coolant test

A test for hydrocarbons or bubbles in coolant; positive results indicate combustion gases leaking through a head gasket, cracked head, or liner seal.

CKP sensor function

The crankshaft position sensor reports engine speed and rotational position to the ECM; without it, the ECM usually will not command injection or ignition.

5V reference circuit

A regulated supply shared by several sensors; a shorted sensor can pull the reference low and cause multiple sensor codes, so check voltage with sensors connected.

CAN bus termination

CAN networks normally use two 120-ohm terminating resistors; with power off, resistance across CAN high and CAN low should read about 60 ohms.

Injector trim code

A calibration code unique to an injector that the ECM uses to correct fuel delivery; after replacement, programming the new code prevents imbalance and misfire.

Accelerator pedal plausibility

The APP sensors are redundant and must agree within a calibrated range; disagreement sets a fault and typically forces limp-home or reduced power.

Voltage drop test

Measuring voltage lost across a connection or cable while current flows; excessive drop identifies high resistance that a static voltage check may miss.

Turbo boost leak

A leak in charge-air pipes or the cooler reduces manifold pressure, causing low power and black smoke; pressure-test the intake tract to locate it.

VGT vanes stuck open

Variable-geometry turbo vanes stuck open reduce exhaust drive pressure and cause low boost and turbo lag; command an actuator sweep and compare desired to actual.

Wastegate stuck closed

A wastegate that cannot open allows turbo speed and boost to rise too high, risking overboost codes, derate, and engine damage.

Turbo shaft play

Excessive radial or axial movement of the turbo shaft indicates bearing wear; wheel contact or oil in charge pipes confirms likely turbo failure.

Exhaust backpressure

Pressure in the exhaust system measured with a gauge; high backpressure from a clogged DPF or crushed pipe reduces power and increases exhaust temperature.

Charge-air cooler leak

A cracked or leaking charge-air cooler lowers boost and can let oily mist escape; pressure testing the cooler and pipes confirms the leak.

Common-rail pressure

Fuel pressure in a common rail can exceed 20,000 psi; high-pressure lines must not be loosened while the engine is running because of injection hazard.

Injector leak-off test

Comparing return fuel volume from each injector; excessive return flow indicates worn injector internals and can cause hard starting, rough idle, or low rail pressure.

Pilot injection

A small fuel pulse before the main injection that reduces combustion noise and NOx; a missing pilot pulse can cause diesel knock and rough idle.

Rail pressure regulator

A valve or metering unit that controls fuel pressure in the rail; the ECM compares commanded and actual pressure to detect supply or injector faults.

Fuel contamination

Water, gasoline, or microbial growth in diesel fuel changes lubricity and combustion; it can damage high-pressure pumps and injectors and cause smoke or power loss.

Injector nozzle coking

Carbon deposits on the injector tip disturb spray pattern and fuel delivery; symptoms include imbalance, smoke, and power loss, often isolated by cutout testing.

DOC function

The diesel oxidation catalyst converts carbon monoxide and hydrocarbons to carbon dioxide and water and raises nitrogen dioxide for passive DPF regeneration.

DPF differential pressure

Pressure measured across the diesel particulate filter; high differential pressure indicates soot or ash restriction, while low pressure can indicate a sensor or hose fault.

Active DPF regeneration

The ECM raises exhaust temperature by post-injection or hydrocarbon dosing to burn soot from the DPF; frequent regens suggest excessive soot production.

DPF ash

Noncombustible material left after regeneration, mainly from oil additives and wear metals; it cannot burn away and permanently increases backpressure.

SCR system

Selective catalytic reduction injects DEF into exhaust to convert NOx into nitrogen and water; NOx sensors monitor efficiency before and after the catalyst.

DEF urea concentration

Diesel exhaust fluid is typically 32.5 percent urea in water; incorrect concentration or contamination can set SCR efficiency codes and cause derate.

EGR cooler leak

A leaking exhaust gas recirculation cooler can admit coolant into the intake, causing white smoke, coolant loss, and misfire; pressure-testing confirms it.