Connecting the Scanner

10-03 Use the scan tool to gather information from the vehicle.

Most engine performance diagnoses will begin by installing a scan tool and checking for codes. After retrieving DTCs, locate the service information for the proper flow chart or pinpoint test. Typically, the diagnostic procedure will involve the technician accessing PID information that relates to the component or system that set the code. PID data are displayed in various forms: voltage, hertz, percentage, milliseconds, and amperage. The concern for the technician is the accuracy of this information and how it is sourced.

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Exercise care when installing the scan tool. A damaged DLC may prevent data from being exchanged between the scanner and the vehicle’s module that is being accessed. If connecting the scan tool changes any of the vehicle’s operating characteristics, disconnect the scanner and retest the module. If the concern is present only when the scan tool is installed, inspect for damaged pins in the DLC or scanner connector. If a scanner fails to communicate with a vehicle and it powers up normally, try installing a different brand of scanner before searching for a vehicle fault.

To access the vehicle’s onboard modules with the ignition turned off, align the connector from the scan tool to the vehicle’s diagnostic connector. Then plug the scan tool into the DLC, exercising care not to force it (FIGURE 10-7). Turn the key on to link the tool to the vehicle. Identify the vehicle’s make, model, and year to the tool. Next, select the module or system to be tested; for drivability concerns, normally start with the engine (manufacturer-specific information) or generic OBD II options. Connect the scan tool and identify the vehicle to the tool to establish a communication link in the correct data language. An exchange of information between the PCM (or another module) and scan tool then occurs. The communication is an exchange of voltage pulses that can be interpreted by the scanner into relevant information and then be displayed for the technician to read. The voltage pulses are also visible when using a DMM or oscilloscope, but they are not relevant as far as information provided. Viewing the changes in voltage only confirms that the network can exchange information; its content, however, is unknown. Think of this communication as a text message being sent between the tool and the module. An OBD II-compliant scan tool is designed to automatically select the correct data protocol.

FIGURE 10-7 When a vehicle comes in with a check engine light on, the technician should plug the scan tool into the DLC located near the steering wheel so that they can access the modules on the network.

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The fuse that supplies power to Pin 16 of the DLC is often shared with other vehicle loads. A common shared power supply is the power point or lighter fuse. For example, a charging cable for a cell phone or other device often shorts internally and may blow a fuse. Check the fuse chart in the owner’s manual or the vehicle’s service information for a shared power input. Also, do not use the power supply pin or either of the ground pins (Pins 4 and 5) to operate additional accessories or devices.

Note: Always verify that the ignition is off before installing a scan tool. Connecting the scan tool to the DLC with the ignition on or the engine running may induce false communication codes (DTCs) into various modules, erase valuable stored data, or cause the vehicle to operate differently. Therefore, always install a scanner with the ignition switch in the Off position.

After identifying the vehicle and linking it to the diagnostic connector, the scan tool can access DTCs, perform bidirectional tests of control systems and inputs to check their operation, and monitor PIDs (TABLE 10-4). The scanner displays the information collected on an LED screen for the technician to read and interpret. In addition to accessing the PCM current, scan tools can access the ABS; air bag/SRS; transmission; electronic suspension; BCM; HVAC; and infotainment systems.

TABLE 10-4 Scanner Connection and Operation Checklist

•Verify that the ignition is off before connecting.

•Check the scan tool cable for damaged, bent, or broken pins.

•Check the DLC connector for damaged pins.

•Verify the orientation of the DLC, align the connector and cable, and then carefully push the connector into place.

•Do not force the cable into the DLC; if it does not fit, examine the cable and connector for a cause.

•If the scanner is not internally powered by batteries and fails to power up after connecting it, check for power at Pin 16 of the DLC.

•Once installed, exercise caution to avoid kicking the cable or connector with the installed scanner, to prevent damaging either component.

•If the vehicle is being test-driven and a corded installed scanner is used, route the cable away from the pedals and steering wheel to prevent an accident.

•If the scan tool being used does not include a Record function when monitoring a PID during a test drive, then for safety reasons, monitor the scan tool while another technician drives the vehicle.

•If a recording of PID data is being made while driving, save it to review it after returning to the shop.

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Do not front probe the DLC pins when checking for power or ground or when testing a system’s network. Inserting the incorrect size of probe can spread the terminal, damaging it and causing a communication issue with the scan tool. Several manufacturers have TSBs stressing this point. Use a DLC BOB or a smart BOB. A smart BOB includes assorted colors of LEDs that light up to indicate power and ground if the circuits are intact. For the communication circuits, a distinct color of LED usually flashes when communication is taking place on the network. If a DLC BOB is not available, then carefully back probe the DLC connector to prevent damaging the pins.

Manufacturer versus Generic Information

There are three levels of scan tools available for technicians and repair shops: OBD II generic, OBD II enhanced, and factory scan tools. The differences between an OBD II generic tool and the enhanced scan tool is that a generic scan tool provides only emissions-based PCM or engine information.

Enhanced scan tools grant access into other systems, including the transmission, ABS, air bag or SRS, HVAC, BCM, and other modules. Some current-model vehicles have more than 75 different modules.

A factory scan tool is specifically made and designed by the OEM manufacturer. Every OEM has its own factory scan tool for use on its vehicles (FIGURE 10-8).

FIGURE 10-8 When diagnosing a vehicle, use the factory scan tool if one is available, to open up more options for diagnostics than a generic scan tool can offer.

Generic Information

By law, all vehicles built in the US since 1996 must contain generic OBD II emissions information. The PCM must provide emission-related data to a certified OBD II-compliant interface tool. The PCM software includes both generic and enhanced (OEM) data. Any OBD II-compliant scan tool and cable will fit any OBD II DLC. To retrieve codes, a professional-grade scan tool or a simple code reader can be used. Generic data include DTCs, data stream information, freeze-frame data (stored in the PCM when a code sets), and information for all the vehicle’s monitors and their status.

The OBD II generic interface performs the following tasks:

A code reader is a basic tool that provides access to the PCM’s emission and engine information. A code reader allows the technician to quickly read and clear DTCs. Most code readers also provide a basic code definition.

Code readers offer various levels of module access and information. The basic functions include reading and clearing OBD II generic codes. Upgraded versions provide code definitions. For an additional cost, a higher-end code reader can include additional information, such as pending codes, freeze-frame data, and permanent codes. The higher-end code readers normally provide the ability to read and clear DTCs in the ABS and air bag system. The basic functions of a code reader prevent it from being used for complex diagnostics. Typically, they do not include data stream information or bidirectional testing. Some code readers that are now available provide OBD II enhanced data, but at a reduced level compared to a fully enhanced diagnostic tool.

Generic data are for emission control systems only. Begin a diagnosis by using the generic mode. Using the generic interface does not require any vehicle information to be entered into the scan tool. Check for DTCs and freeze-frame data. Always record this information for later use. Note: Remember that if the codes are cleared or if battery power is removed, this information will be lost. Next, check the generic data stream; it is typically sufficient to diagnose and repair most faults. Although the number of PIDs is limited compared to enhanced data, generic information focuses on the most important inputs and commands. An additional benefit of the generic data stream is that substituted sensor data won’t affect the diagnosis.

If after using the generic interface, additional information is required to switch over to the OEM-enhanced interface. Generic data are often limited when compared to enhanced data involving non-emission-related systems that require access to the vehicle’s enhanced interface. Note: When entering the enhanced interface, identify the vehicle to the scan tool if this has not already been done.

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Many aftermarket scan tools list OEM and generic OBD II options separately. To use a scan tool, connect it to the DLC and select the desired function. Other vehicles may have two separate test connectors. One is the mandated OBD II connector; the other requires a special adapter for OEM functions.

Enhanced or Manufacturer-Specific Information

Enhanced or manufacturer-specific (OEM) interfaces provide additional emission data and frequently contain information on non-emission components, access to other vehicle modules, and bidirectional tests. Most professional-grade scan tools include both generic and enhanced interfaces, facilitating moving back and forth between the two interfaces. Manufacturer-specific interfaces are accessed through the DLC on most vehicles. However, some manufacturers include a separate diagnostic link. Remember that when obtaining OEM-level information, enter the vehicle information into the scan tool, including vehicle make, model, and year.

Bidirectional testing provides a technician with two actions to perform: actuator testing and adjustments. Bidirectional actuator testing allows the technician to use a scan tool to complete an action on the vehicle. For instance, if a fuel pump is not working, it could be a faulty pump, wiring, relay, or command. By turning the fuel pump on and off using the scan tool, most of the possible faults can be eliminated (FIGURE 10-9). If the pump runs, then there is an issue with the module commanding the pump on. If the pump still fails to operate, checking power and ground at the pump connector while bidirectionally controlling the fuel pump will determine whether it’s a wiring, relay, or pump issue. If power and ground circuits pass a circuit load or voltage drop test, suspect a faulty fuel pump.

FIGURE 10-9 A factory scan tool allows the technician more control than a generic scan tool, but the former may not always be available to the technician in the repair facility.

Some higher-end scan tools do include enhanced-level diagnostic capability but lack the proprietary advantages of an OEM scan tool. Enhanced data provide access to systems other than powertrain emission functions. OEM-level interfaces typically require a manufacturer-specific scan tool to access all available options. Factory scan tools can communicate with all the vehicle’s modules, including the PCM. The features of OEM diagnostics, regardless of the module involved, include an increase in the number of PIDs available for diagnosis, make and model bidirectional testing, OEM-level testing of components or systems, and module programming, which is not available in generic OBD II.

Another function of some enhanced and all OEM scan tools is reprogramming, also known in OBD II terms as J2534 reflashing. J2534 programming is an SAE standard allowing aftermarket technicians to reprogram a vehicle’s engine computer. An increasing number of modules require updated software for a variety of vehicle conditions that are affected by a module’s calibration. The only way to repair a fault if the software is corrupted or incorrect is to reprogram it. These updates are typically part of an OEM TSB to replace defective files in the module’s software with OEM files that are downloaded from the Internet (FIGURE 10-10). Also, as vehicle complexity increases, part replacement may require programming. Many new components require a relearning process or require the vehicle’s information to be downloaded into it via programming before it will function correctly.

FIGURE 10-10 Replacing a module usually requires programming it to the vehicle and inputting the proper software to make it operate. If it is not programmed properly, the new module will not operate and the repair will not be complete.

To access enhanced data, the vehicle’s vehicle identification number (VIN) information must be entered into the scan tool. The data required include the vehicle’s make, model, and year. Late-model OEM systems and scan tools with the appropriate software typically automatically identify the vehicle. Automatic identification prevents having to enter the information manually.