Wrap-Up

Ready for Review

• Diagnostic trouble codes provide the technician direction in diagnosing the fault with the vehicle.
• Trouble codes have a universal understanding in OBD II vehicles.
• One-trip DTCs illuminate the check engine light after one failed drive cycle.
• Two-trip DTCs illuminate the check engine light after two failed drive cycles.
• Freeze Frame data is a capture of the data set when the code was set.
• Misfire Freeze Frame data sets up the necessary information needed to diagnose a misfire.
• Code identification allows the technician to process what system the code is from.
• Basic diagnostic steps include looking at the basic areas of faults on the vehicle to examine if it is the source of the issue.
• Parameter Identification (PID) gives the technician information of different aspects of vehicle operation.
• When starting with a DTC, gaining as much information as possible about it should be the goal of the technician.
• When starting with no DTC, the technician should rely on their understanding of the various systems on the vehicle to direct them into a diagnostic plan.
• Enhanced trouble code menus within the scan tool help to direct the technician.
• Failure records are recorded so that the technician can replicate the conditions when the code is set.
• After clearing the code it is recommended to run through a drive cycle to reset the monitor.

Key Terms

Diagnostic Trouble Code (DTC)  A code logged by the electronic control module when electrical faults or system problems occur in commercial vehicle control systems.

Freeze Frame data  A snapshot of the conditions present when the DTC was stored.

History DTCs  Codes that were out of parameter at one time but are not currently out of range.

keep alive memory (KAM)  Memory that is retained by the ECM when the key is off.

Pending DTCs  Codes that failed the first monitor but have yet to fail a second monitor to become a hard code.

Permanent DTCs  Codes that require running the monitor associated with the code until it passes; it cannot be cleared with a scan tool.

Review Questions

1. A one-trip DTC is a situation where the monitor looks at the data PIDs and determines that:
   • In one trip the engine fails to meet the monitor goals
   • The driver didn’t complete one-trip test
   • The monitor is not important enough to be a two-trip DTC
   • A soft fault has occurred
2. A PID refers to what on an OBD II system?
   • Personal Identification Device
   • Parameter Identification
   • Power Inverter Disabled
   • Problem Identification
3. Freeze Frame data allows the technician to:
   • Determine how cold the vehicle has been
   • View what the vehicle was doing when the DTC triggered
   • Capture all of the operation information for the engine
   • Tell the technician where the vehicle has been
4. When trying to diagnose an engine problem with no codes, the first step should be to:
   • Replace the PCM
   • Replace a fuel injector
   • Conduct a visual inspection
   • Determine if the engine has a bad battery
5. When manufacturers use enhanced Freeze Frame, they provide the technician:
   • Decreased information as it is proprietary
   • More information that is related to the fault
   • No more information than regular Freeze Frame
   • Useless information
6. What type of DTC sets after one-trip failure?
   • A
   • B
   • C
   • D
7. Keep alive memory is used to retain what within the PCM?
   • Software programming
   • DTCs
   • Adaptives that have been learned from operation of the vehicle
   • The radio memory
8. During the at-wide, open throttle, the throttle position sensor is close to what voltage?
   • 1.5 V
   • 2.5 V
   • 4.5 V
   • 3.5 V
9. Reading the code description helps the technician to understand:
   • How the monitor operates and what causes the code to set
   • What the PCM operational strategy is
   • How the engine operates
   • Failure records
10. Code identification helps the technician determine which module the code is from. What letter designates PCM?
    • C
    • B
    • P
    • U

ASE Technician A/Technician B–Style Questions

1. Technician A says that Freeze Frame data is useful to determine how many codes there are in the vehicle. Technician B states that understanding what sets the code allows the technician to diagnose it quickly. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
2. Technician A says that keep alive memory is where the adaptive memory is housed. Technician B states a pending code has only failed one time and it is waiting for the monitor to fail again before becoming a hard code. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
3. Technician A says that the misfire monitor tells the technician that there is a fault but does not identify the fault. Technician B states that diagnosing a no-code condition should start with replacing the PCM. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
4. Technician A says that a history code is one that has set on a previous ignition cycle. Technician B states that creating a diagnostic plan based on the trouble code is the correct way of fixing the fault. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
5. Technician A says that code set conditions are not a concern for the technician. Technician B says that a B type code is a two-trip setting fault code. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
6. Technician A says that clearing DTCs is the first action that should be performed when a vehicle comes in. Technician B says that U codes should be diagnosed first before anything else. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
7. Technician A says that completing a drive cycle will run all of the continuous monitors so a correct repair can be validated. Technician B says that a pending DTC may go away if the monitor runs successfully the next time it runs. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
8. Technician A states that code identification is key to going down the right path to diagnose vehicle issues. Technician B says that using manufacturer-enhanced information helps with quickly identifying the PID that will provide the most information about the fault. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
9. Technician A states that without DTCs present the technician must fall back on their understanding of the various systems of the engine. Technician B says that everything that fails produces a DTC and that the technician should only fix those items that are on the code list. Who is correct?
   • Tech A
   • Tech B
   • Both A and B
   • Neither A nor B
10. Technician A says that to clear the PCM codes the technician should use a scan tool to actuate the clear codes function. Technician B says that operating the vehicle in conditions that are opposite of the Freeze Frame data will allow the vehicle to reset. Who is correct?
    • Tech A
    • Tech B
    • Both A and B
    • Neither A nor B