Vehicle Management Systems Flashcards
Which of the following conditions would be the likely cause of a “hard to start” complaint that only occurs when the engine is at operating temperature?
“A. Retarded ignition timing
B. Advanced ignition timing
C. Shorted crankshaft position sensor
D. Fuel contamination of engine oil”
“Answer B
Advanced ignition timing is a common cause of a warm engine, ““hard to start”” complaint on an engine that starts easily when cold. “
A standard oxygen sensor is producing an average reading of 450 mV on an engine that is at operating temperature and assumed to be in closed loop mode. What should happen to the voltage reading if you create a vacuum leak by disconnecting a small vacuum hose?
“A. Nothing
B. Voltage reading goes up
C. Voltage reading goes down
D. Engine stalls “
“Answer C
A vacuum leak is a common cause of a low O2 sensor output reading. The result is interpreted by the engine controller as a lean burn condition, and it accordingly overfuels the engine.”
Which of the following input sensors should produce nearly identical readings on a vehicle at the moment of start-up after being shut down for 12 hours?
“A. MAF and MAP
B. ECT and IAT
C. DTC and TPS
D. VSS and CKP”
“Answer B
ECT and IAT should produce equal readings after a prolonged shutdown period. Learn the common OBD II acronyms and the roles they play. “
How many pins are in an OBD II-compliant data link connector?
“A. 2
B. 8
C. 16
D. 32”
“Answer C
There are 16 pins in an OBD II- compliant data link connector”
What is the minimum number of data freeze-frames captured by an OBD 2-Complaint vehicle after a DTC is set?
“A. No minimum
B. 1
C. 2
D. 8”
“Answer B
The minimum number of date freeze-frames captured by and OBD II-compliant vehicle when the PCM logs a DTC is 1. However, most current systems are capable of logging a greater number of freeze-frames, although a proprietary scan tool may be required to access them. “
Which vehicle system do all OBD-II Type A and B diagnostic trouble codes relate to?
“A. Engine
B. Exhaust
C. Emissions
D. Climate control”
“Answer C
All OBD II Type A and B diagnostic trouble codes relate directly or indirectly to the emission control system. Most current vehicles use SAE J1850 data bus (multiplexing) protocols, but OEMs are only required to make OBD II conditions readable on generic scan tools: a J1850 data bus is capable of displaying detailed data on all the vehicle computer-control circuits, but in most cases proprietary PC software or scan tools are required to read this data.”
Which pin in a standard 16-pin, OBD 2-Complaint data link connector is reserved for chassis ground?
“A. 2
B. 4
C. 8
D. 16 “
“Answer B
A standard 16-pin, OBD II-compliant data link connector dedicates pin #4 for chassis ground. You should learn the pin assignments for Bus + (2). Bus - (10), chassis ground (4), and signal ground (5): note that Bus - usually carries some voltage potential. “
How is a warm-up cycle defined for purposes of OBD II code log clearance?
“A. 3 consecutive key-on/ key-off cycles
B. Coolant temperature increase of at least 22°C (71.6°F)
C. Coolant temperature exceeds 70°C (158°F)
D. Coolant temperature exceeds 70°C after an increase of at least 22°C “
“Answer D
A warm-up cycle is defined for purposes of OBD II code status as an event in which the engine coolant temperature increases by at least 22°C (71.6°F) and in doing so, exceeds 70°C (155°F). For instance, an MIL (malfunction indicator light) will deactivate after the PCM monitors 3 consecutive warm-up cycles through which a DTC is not detected. Once the MIL has been deactivated, the DTC will be logged in memory for a further 40 warm-up cycles before it is erased.”
if you unplug a coolant temperature sensor terminal from the coolant sensor on a warm engine, which of the following would result?
“A. The engine will automatically shut down
B. Coolant temperature is displayed on scan tool at the highest possible reading
C. A DTC is set indicating an open
D. A DTC is set indicating voltage high
“
“Answer C
If a coolant temperature sensor terminal is unplugged from the coolant sensor on a warm engine, the result is to log a DTC indicating an open (voltage low) and the displayed scan tool reading will usually be at the minimum value.”
Which of the following conditions would be more likely to account for a low output voltage from a standard O2 sensor located upstream from the catalytic convertor?
“A. Plugged catalytic convertor
B. Restricted exhaust system
C. Failed air injection circuit
D. Cracked exhaust manifold”
“Answer D
A low output voltage from a standard O2 sensor suggests a lean condition. There are 2 causes of a ““false”” lean condition: one is a dead cylinder, meaning that unreacted oxygen is dumped into the exhaust; and the other is air being pulled into the exhaust system, so a cracked exhaust manifold is a likely cause. The other conditions are more likely to result in a higher O2 voltage.”
Which of the following running coniditons would be more likely to require richer than stoichiometric air-fuel mixture?
“A. normal cruising
B. Light load Operation
C. Deceleration
D. Idling “
“Answer D
Depending on the specific engine and fuel system, the range of air-fuel ratios runs from about 8:1 up to 17:1. Generally, a leaner mixture is required for normal cruising and light load operation, while a richer than stoichiometric mixture is required for idling, heavy load, and hard acceleration. Make sure you know how to define stoichiometric. “
The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required.
An engine fuelled with 89 octane gasoline pings especially when accelerated. The fuel is specified as a 10% ethanol cut. Which of the following would be more likely to remedy the condition?
“A. Advance the base ignition timing
B. Change to a higher octane-rated fuel
C. Change to a lower octane-rated fuel
D. Change to an ethanol-free gasoline”
“Answer B
Changing to a higher octane fuel is the only answer that makes sense. Many fuels sold today are cut with ethanol: ethanols usually have a higher octane rating than gasoline but in the question stem, the octane rating is specified. Ping or knock is caused by too rapid combustion of the fuel; it can be remedied by increasing the octane rating or retarding ignition timing. “
What should result when the vacuum hose on the fuel regulator on a port-injected fuel injection system is removed?
“A. Fuel rail pressure decreases
B. Fuel rail pressure increases
C. Fuel rail pressure unaffected
D. Engine stalls “
“Answer B
The fuel rail pressure should increase when the vacuum hose is removed from the regulator. When system vacuum drops off as when the throttle is fully opened, the regulator responds by stepping up rail pressure. Make sure you understand how a fuel regulator operates: this is a common source of AST C of Q questions. “
While performing a noid light test to diagnose a fuel injector problem, the noid light illuminates but appears to dim. What condition is indicated?
“A. High resistance in the fuel injector coil
B. Short circuit in the fuel injector harness
C. Short circuit in the fuel injector coil
D. High resistance in the fuel injector wiring or connector”
"Answer D A noid (short for solenoid) light test is used to diagnose fuel injector circuit malfunctions: the fuel injector is disconnected and the noid light placed in the A circuit. The noid light should illuminate in sequence when the engine is run. A noid light that illuminates but appears to dim suggests high resistance in the fuel injection wiring circuit: it cannot suggest an injector coil problem because to insert the noid light into the circuit, the fuel injector has to be disconnected."
A gasoline fuel pump produces a whine from the fuel tank when it operates. Which of the following should be performed before making the decision to replace the pump?
“A. Replace the fuel filter
B. Replace the fuel regulator
C. Replace the fuel tank
D. Replace the fuel injectors”
“Answer A
A restricted fuel filter may cause a rise in fuel pressure, slowing and overloading the fuel pump in some OEM models. You can verify the problem by checking fuel flow volume downstream from the filter. Note that one OEM had a problem with fuel pump whine in the 1990s that is not associated with reduced flow.”
You have electrically tested a set of injectors on a V6 engine with around 200,000 km on the odometer and found a 3 to be defective to the point of requiring replacement. Which of the following would be the correct procedure?
“A. Keep testing the 3 good injectors to see if you can make them fail
B. Replace the solenoids on the 3 defective injectors
C. Recommend that a set of 6 new injectors be installed
D. Switch the locations of the 3 good and 3 defective injectors”
“Answer C
In this situation, you should recommend that all 6 fuel injector be replaced given the mileage on the vehicle, fuel balance considerations, and the fact that purchasing a full set of injectors is more economical than purchasing them in smaller numbers. Note that gasoline fuel injectors are seldom repaired in the field; they are removed and replaced by the technician.”
When a vacuum hose is removed from a vacuum-modilated fuel pressure regulator, a small quantity of fuel drips from the hose. which of the following is the more likely cause?
“A. Excessively high rail pressure.
B. Leak in the fuel rail return circuit
C. Leak in the regulator diaphragm
D. Restriction in the fuel rail inlet”
“Answer C
When fuel drips from the vacuum hose that connects to a vacuum-modulated fuel pressure regulator when it is disconnected, the cause is usually a failed regulator diaphragm. “
When scoping a pulse width-actuated injector, where should the inductive kick (spike) occur on the graphic?
“A. At the end of the pulse width profile
B. At the centre of the pulse width profile
C. At the beginning of the pulse width profile
D. Profile should be entirely ““square”” if the injector is good”
“Answer A
When scoping a pulse width-actuated injector, the inductive kick (spike) occurs when the injector coil is de-energized and its magnetic field collapses. It should therefore occur at the end of the pulse width on the display graphic.”
You are Scoping one of a set injectors in a port-injected fuel system and observe the inductive kicks displayed in the graphic to gradually reduce in length as the engine warms to operating temperature. what is the likely cause as the engine warms to operating temperature. what is the likely cause?
“A. Short in the injector coil
B. Open in the injector coil
C. High resistance in the injector coil
D. Injector pulse width is shortened as the engine reaches operating temperature”
“Answer D
The inductive kick displayed in a scope graphic of injector pulse width will be observed to gradually reduce in length as the engine warms to operating temperature because the coil is energized for a shorter period when the engine is at operating temperature. Note also that pulse width real-time duration will also reduce. “
If the oxidizing stage of a catalytic convertor on on a gasoline engine is function properly, which of the following should be true regarding exhaust gas temperatures once the engine is at operating temperature?
“A. Convertor in should be 15% warmer than convertor-out temperature
B. Convertor in and out temperatures should be equal
C. Convertor out should be 15% warmer than convertor-in temperature
D. Convertor should be cool enough to touch by hand”
“Answer C
If the oxidizing stage of a catalytic converter on a gasoline engine is functioning properly, the exhaust gas temperature at the converter outlet should be greater than that at the inlet because in essence, unburned HC and CO are being combusted in the converter. The differential should be around 15% once the engine is at operating temperature and under normal loads, but there are many variables here.”
Which type of ignition system eliminates spark plug wires?
“A. COP (coil on plug)
B. DIS
C. Direct fire system
D. Contact point systems”
“Answer A
A coil-on-plug ignition system eliminates spark plug wires. This is one of the more common ignition systems today. “
Which of the following must be true of the shield used on an optical ignition sensor?
“A. It must be airtight
B. It must be periodically replaced
C. It must be lightproof
D. It must be lubricated with engine oil prior to installation”
“Answer C
The shield used on an optical ignition sensor must be lightproof. If this is left off, the results will be rough engine operation”
When troubleshooting a distributorless ignition system you identify a defective high-tension wire. Which of the following should be replaced along with the wire?
“A. Spark plug
B. Coil
C. Ballast resistor
D. Distributor pick-up coil”
“Answer B
A defective high-tension wire almost always destroys the coil that fires it. The high voltage produced by the coil, deprived of its intended ground path, arcs within the coil, creating a short circuit to the primary windings known as a carbon track.”
What switches primarily circuit current in the ignition module in a typical electronic ignition circuit?
“A. Transistor
B. Hall-effect switch
C. Optical switch
D. Electro-mechanical switch”
"Answer A A transistor switches primary circuit current in the ignition module in a typical electronic ignition circuit. Transistors are solid-state components that act like an electronic relay switch: they allow the ignition module to signal the primary transistor with a low-potential voltage"
When platinum spark plugs are to be reused, which of the following is correct procedure?
“A. Regap to specification
B. Coat threads lightly with anti-seize compound and do not attempt to regap.
C. Apply 10% more than original specified torque
D. Glass bead blast the electrodes “
“Answer B
When platinum spark plugs are to be reused, the threads should be lightly coated with never-seize compound (because they require so little service attention and are more likely to seize) and no attempt should be made to regap them. If the gap is well outside specification, replace them. “
When scoping a good pair of plugs on a waste spark ignition system, what should distinguish the power spark from the waste spark on the oscilloscope pattern?
“A. Firing line is higher on the power plug
B. Firing line is lower on the power plug
C. Intermediate oscillation diminish more rapidly on waste plug
D. Both patterns should be nearly identical through the cycle”
“Answer A
When scoping a good pair of plugs on a waste spark ignition system, the power spark is distinguished from the waste spark on an oscilloscope display by a higher firing line. This is caused by increased cylinder pressure, meaning that the voltage required to maintain the spark is increased “
When you disconnect a high-tension wire on a running engine while troubleshooting an ignition problem, what must you do?
“A. prevent the high-tension wire from the contacting ground
B. disconnect the ignition module
C. ground the spark plug with a jumper wire
D. Ground the high-tension wire”
“Answer D
When you disconnect a high-tension wire on a running engine during troubleshooting, you must ground the wire. Failure to do so can destroy the ignition coil (See the explanation for question #50 of this test).”
Which of the following could contribute to a lean air-fuel mixture in a sequential port, gasoline fuel-injection system?
“A. Restricted air filter
B. Leaking lower injector seal
C. Leaking upper injector seal
D. Broken air duct before the mass airflow sensor”
“Answer B
The lower injector seal in a sequential port, gasoline fuel injection system is a seal between atmosphere and the intake manifold. A leaking lower injector seal will therefore allow unmetered air into the intake causing a leaner air-fuel mixture. “
What does a flashing MIL (malfunction indicator lamp) indicate on an OBD 2-complaint vehicle?
“A. Misfire that could cause catalytic converter damage
B. Type A code
C. Type B code
D. Internal PCM failure “
“Answer A
A flashing MIL indicates that there is an engine misfire that at the current engine speed and load conditions could cause catalytic converter damage”
What does an STFT ( short-term fuel trim) value of -10% indicate?
“A. Oxygen sensor is signalling a high voltage condition
B. PCM is subtracting the fuel to lean out mixture
C. PCM is adding fuel to enrich mixture
D. System is not in closed loop yet”
“Answer B
The STFT number of -10% indicates that the PCM, on signal information from the oxygen sensor, is operating in closed loop, and is subtracting fuel out of the mixture to lean the AFR. “
If an EFI engine has adequate spark and fuel pressure, but still does not start, which of the following is the most likely cause?
“A. TPS signal wire shorted to ground
B. TPS signal wire shorted to 5V reference
C. Disconnected oxygen sensor
D. Fuel pump relay failure”
“Answer B
If the PCM reads throttle position as being wide open, the PCM shuts off the injector pulse and goes into (clear floor) mode. A shorted signal wire to 5 volts would signal the PCM that the throttle was wide open “
When testing a pulse generator type crankshaft position sensor, what should the output be during cranking?
“A. 500-1500 w
B. 1-2 V-DC
C. 1-2 V-AC
D. 1-2 AMPS”
“Answer C
A magnetic pulse generator would typically produce 1-2 V-AC during cranking. “
