Wrap-Up

Ready for Review

• The DLC is where the scan tool hooks up and information can be extracted from the vehicle.
• OBD II started in 1996, which created a set of standard communication protocols.
• OBD II protocols change the speed of the network and physical makeup.
• Multiplexing is used to minimize the use of wires.
• The CAN has two 120 Ω terminating resistors wired in parallel.
• Some networks have a gateway module that interprets different networks and translates to others.
• CANs are at rest at 2.5 V.
• No-communication codes in modules are usually the result of no communication with another module, not the module they are in.
• There are phantom U-codes that are not hard faults, and they need to be diagnosed.
• The network topology map can help with diagnosing network faults.
• Use a scan tool to understand which modules are having the communication problem.
• A lab scope can be used to view the communication between modules to check for shorts to ground or power.
• LINs are used to help take the load off of the CAN for nonessential items.
• Use a DVOM to test for power and ground on the network.
• Use a DVOM to test the terminating resistors and network integrity.

Key Terms

antilock brake systems (ABS)  A safety measure for the braking system that uses a computer to monitor the speed of each wheel and control the hydraulic pressure to each wheel to prevent wheel lockup.

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; it is used to manage the ABS.

electromagnetic interference (EMI)  A small electromagnetic field, which can interfere with other electronic devices because of the magnetic wavelengths produced; it is generated by every electronic device.

high-speed controller area network (HS-CAN)  A wire data network in vehicles that is used to connect control modules so that they can communicate quickly and easily.

local interconnect network (LIN)  A network designed by a consortium of automakers to provide the benefits of CAN but at a lower speed and lower cost. LIN uses a single-wire communication line.

modules or nodes  An electronic computer or circuit board that controls specific functions.

supplemental restraint systems (SRS)  A passenger safety system, such as airbags and seat belt pretensioners.

Review Questions

1. When a controller area network (CAN) is present on a vehicle, the network wiring is twisted to help combat what?
   • Shorts to ground.
   • Electromagnetic interference (EMI).
   • Cross power distribution.
   • Wiring getting caught in other components.
2. All of the following statements with respect to network communications are true except:
   • Networking the modules on the vehicle increases the number of wires present.
   • Communication between modules allow for more efficient vehicle operation.
   • CAN HI and LO are at rest at 2.5 V.
   • A universal asynchronous receiver-transmitter (UART) is a single-wire communication protocol.
3. A network topology map can be used for __________.
   • finding a place to add a module
   • determining where the module is located in the vehicle
   • nothing
   • identifying the gateway module
4. When using a lab scope to verify communication on the CAN, what should be looked for?
   • 12 volts on the network.
   • A crisp square wave of approximately 5 volts negative to positive.
   • A 26-volt square wave.
   • Alternating current (AC) voltage.
5. Pin 16 on an OBD II DLC is used for _________.
   • unswitched 12 V
   • switched 8 V
   • ground
   • CAN HI
6. When the CAN is shorted to ground, what can happen to the networked modules?
   • Nothing.
   • It can generate false information that can cause other issues with the vehicle.
   • It can allow the body module to take over operational duties of the network.
   • A networking fault light can come on.
7. When a CAN is at rest and no communication is happening, what should be the voltage on Pins 6 and 14 of the DLC?
   • 12 volts.
   • 5 volts.
   • 2.5 volts.
   • 8 volts.
8. If the vehicle doesn’t have the correct battery voltage to the modules, the communication networks may not have enough power to operate properly. What should the battery voltage be if it is fully charged?
   • 12 volts.
   • 12.6 volts.
   • 14.4 volts.
   • 12.1 volts.
9. When using a scan tool on a no-communication fault, where the scan tool cannot communicate, the technician should verify that the scan tool ____________ another vehicle.
   • communicates with
   • plugs into
   • turns on
   • retrieves codes for
10. A connector on the network is heavily corroded from water intrusion. This connector could cause skewed communication signals.
    • True.
    • False.

ASE Technician A/Technician B–Style Questions

1. Technician A says that a terminating resistor is 120 Ω, so an ohms test of the CAN is needed to determine whether it has the required 120 Ω. Technician B says that the twisted wires used on the CAN help with limiting EMI. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says that UART is not used on engine control modules anymore. Technician B says that UART is used for module-to-module communication. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says that scoping the communication lines should be done to determine whether the modules are communicating with each other. Technician B says a communication line that is shorted to power will look like a solid 12 V line on the scope. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says a LIN is used for nonessential systems and lightens the load on the CAN. Technician B says that a gateway module may have more than one type of communication standard coming into it. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says that using a simple DVOM can verify power and ground on the communication network. Technician B says a scan tool may be the cause of a no-communication issue with the vehicle. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says the model year 1998 was the first year for On-Board Diagnostics second generation (OBD II) datalink connectors (DLCs). Technician B says CAN protocol became a requirement in the 2008 model year. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says networking modules allow the vehicle to react to situations that are present in other areas on the network. Technician B says having a charging system that will not maintain the proper voltage can cause networking issues. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says using a DLC breakout box (BOB) will help to maintain the terminals in the DLC connector. Technician B says not to diagnosis a U-code unless it relates to the module suspected of having a problem. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says to clearly understand what the complaint with the vehicle is before trying to diagnose a networking problem. Technician B says that serial data are simpler forms of communication, which are slower than CAN data. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says that using a module topology chart can help with diagnosing communication line faults. Technician B says the Society of Automotive Engineers (SAE) sets standards for communication networks so that there is some commonality among makes. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B