Wrap-Up

Ready for Review

• The powertrain control module (PCM) controls the output functions of the various engine-related operational components.
• The inputs provided to the PCM allow it to determine the proper outputs to ensure that the engine operates correctly.
• Relays are used to control high-amperage components with lower-amperage switches.
• The PCM controls ignition to coordinate it with the fuel-injection events.
• Idle speed is controlled in a couple different ways: one with an idle air control (IAC) motor and the other through the throttle actuator control (TAC) motor.
• The sensors on the engine can be a combination of analog and digital signals.
• The PCM converts the analog signals to digital so that it can make decisions based on them.
• The electronically erasable programmable read-only memory (EEPROM) is where the calibration is stored inside the PCM.
• The output drivers control the different components of the engine to maintain engine operation.
• Calibrations are the software programs that operate the engine or the modules that they are put into.
• Calibrating the module to new sensors occurs when the module learns the position of the new component.
• When replacing the calibration, the program needs to be reflashed to install it into the module.
• There are sometimes updates to calibrations that fix software bugs present in the pre-updated software.

Key Terms

calibrating  A procedure performed to match electronic input and output values to ECM software.

calibration  The software that operates the module and controls its outputs in the vehicle.

electronic control module (ECM)  A computer that receives signals from input sensors, compares that information with preloaded software, and sends an appropriate command signal to output devices.

electronically erasable programmable read-only memory (EEPROM)  Nonvolatile memory technology that is used to store operating instructions or programming for an ECM.

flashed  a generic term of replacing or introducing the software necessary to make the control module operational.

idle air control (IAC) motor  A stepper motor–controlled idle motor that controls the air that bypasses the throttle blades to keep the engine running when the throttle is closed.

long-term fuel trim (LTFT)  A projected fueling need calculated by taking into account the operational situation of the engine. This is a learned value.

output driver  A device, usually a type of transistor, that controls an output device, such as the blower motor, an interior light, or a fuel injector.

relay  An electromechanical switching device whose magnetism from a coil winding acts on a lever that switches a set of contacts.

SAE J2534 standard  The SAE standard that defines what type of interface is required to reprogram engine control units. This is a governmental regulation that allows non-OEMs to repair PCM-related emission issues.

short-term fuel trim (STFT)  The computer’s immediate response to change the air-fuel ratio by controlling injector on time based on the oxygen sensor’s input.

stepper motor  A specialized DC motor that has a rotor operated by a series of coils that surround the rotor. The rotor is stepped, or moved incrementally, by pulsing the coils in sequence, causing the rotor to move in a specific direction and amount of rotation. The coils can be pulsed in either direction, so the rotor can move clockwise or counterclockwise. These motors are often used to move a component a very specific amount for precise control of the related output system, like the doors in heating and air conditioning duct work.

throttle actuator control (TAC) motor  The housing on an intake manifold that is used to control the amount of filtered air that enters the cylinders. This is controlled by a stepper motor and two TPSs and is commanded by the PCM to a particular position. It is also called a drive-by-wire system.

transistor  A semiconductor device usually made with three layers of doped silicon material. Bipolar transistors can be constructed as positive-negative-positive (PNP) or negative-positive-negative (NPN) types. A transistor has a base, collector, and emitter. A small current at the base controls a larger current through the collector and emitter. The emitter is denoted by an arrow, which usually points toward the ground portion of the circuit.

Review Questions

1. A transistor is used to actuate various components on the engine because of _______________.
   • the quickness of the switch, since it has no moving parts
   • the high-amperage capacity of the switch
   • how easy it is to replace if it fails
   • the mechanical capacity of the switch
2. All of the following statements regarding fuel-injection output signals are true except:
   • The powertrain control module (PCM) uses relays to control electrical components to minimize the possibility of voltage spikes in the module.
   • Ignition control by the PCM is used to operate the crankshaft position (CKP) sensor.
   • A stepper motor is used to position a component in a particular position.
   • The throttle actuator control (TAC) motor replaces the conventional throttle blades that are operated by a cable.
3. A relay is a switch that ____________________.
   • is used because of the absorbent glass mat (AGM) battery in the vehicle
   • uses high current to control a low-current component
   • uses low current to control a high-current component
   • turns on a device
4. Choose the correct statement.
   • The TAC motor uses a throttle cable to calibrate it.
   • The calibration in a module is generic operational software that is the same for every application.
   • The PCM controls ignition coils on coil-on-plug (COP) ignition systems.
   • The idle air control (IAC) motor is a normal DC motor that is either on or off.
5. The SAE J2534 standard allows the technician to ___________________.
   • communicate with any vehicle with one device on that standard
   • repair the vehicle with parts not from the original equipment manufacturer (OEM)
   • increase the performance of the PCM by adding an extra module
   • do nothing more than without it; the SAE J2534 standard will not help the technician
6. The TAC motor is used to control the operation of ______________.
   • the fuel-injection pump
   • the throttle blades
   • the intake manifold runners
   • the exhaust gas recirculation (EGR) valve
7. Choose the correct statement.
   • The TAC motor takes the place of the throttle cable.
   • Transistors are high-amperage switches.
   • Relays have no moving parts.
   • The ignition is controlled mechanically off of the crankshaft.
8. The ignition coil is controlled by a driver in the PCM, which does not have a relay in series with the driver. Why?
   • There are no relays that can handle the increased amperage.
   • It needs precise control to activate the ignition coil.
   • The primary side of the ignition coil is not a high-amperage component.
   • The secondary side of the ignition coil is controlled by the transistor.
9. The PCM likes to detect digital signals because they make the decision process simpler. How does it interpret analog signals?
   • It ignores them and doesn’t use them in its decision process.
   • It converts them to digital ones that it understands.
   • It’s not good information anyway, so it makes decisions based only on the digital signals.
   • It uses a chart to determine where the component is on the analog scale.
10. By using a J2534 communication tool, the technician can __________.
    • change the sensors output signals
    • change which signals the PCM uses to make decisions
    • do nothing
    • program the operation software into the PCM

ASE Technician A/Technician B–Style Questions

1. Technician A says OBDII-equipped vehicles allow the technician to reprogram the PCM with a J2534 device. Technician B says the IAC motor is a simple DC motor that has only an on and off feature. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says that electronically erasable programmable read-only memory (EEPROM) is not erasable and that the module will need to be replaced if the calibration loaded onto it is bad. Technician B says some new sensors must be calibrated to the module on the vehicle so that it recognizes the new normal. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says that when reprogramming the PCM, the technician should look for the oldest calibration file to use. Technician B says transistors are low-amperage switches with no moving parts. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says analog signals from sensors are converted inside the PCM to digital ones. Technician B says the driver controls the IAC motor by using the accelerator pedal position (APP) sensor on the accelerator pedal. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says the CKP and the camshaft position (CMP) sensors control the operation of the ignition coil. Technician B says a module may need to be recalibrated when components are replaced on a system. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says the PCM is the operational component that takes inputs from various modules on the vehicle to operate the engine correctly. Technician B says relays are controlled by the drivers in the PCM. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says the output drivers control everything that the PCM can control. Technician B says the aftermarket component makers create the updated software in order for the PCMs to fix errors created by the OEMs. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says that a stepper motor is used when the component has to spin continuously when it is powered on. Technician B says that the primary side of the ignition coil is a low-amperage circuit. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says that when an output driver has failed in the PCM, it can be replaced with a bigger one that can handle increased power. Technician B says controlling the idle speed is not necessary for engine operation. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says that monitoring the failures of the engine will allow the PCM to modify the output drivers to try to correct the condition. Technician B says the PCM usually controls the ground side of the component. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B