ASE L1 Domain 2: Computerized Powertrain Controls Diagnosis

A vehicle's OBD II system has triggered a DTC P0131, indicating a low voltage condition for the pre-catalytic converter oxygen sensor (Bank 1, Sensor 1). After verifying the sensor's voltage supply and ground, what should be the NEXT step in diagnosis?

A technician is diagnosing a DTC P0171 - System Too Lean (Bank 1). If the fuel trim data shows high positive values at idle that begin to normalize at higher RPMs, what is the MOST likely cause?

On a vehicle equipped with a CAN (Controller Area Network) system, a technician has trouble communicating with the powertrain control module (PCM) using a scan tool. There are no drivability problems or other module communication issues. What should be checked FIRST?

When diagnosing an engine performance issue, a technician finds a DTC P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient. The EGR valve and passages have been checked and are operating correctly. What is the NEXT step in diagnosis?

A scan tool displays a DTC P0325 - Knock Sensor 1 Circuit (Bank 1). There is no engine knocking present. What should be the technician's NEXT step?

During a road test with a scan tool, a technician observes that the throttle position sensor (TPS) voltage does not exceed 3.5 volts at wide-open throttle (WOT). The specified range is 0 to 5 volts. What is the MOST likely cause of this condition?

When a vehicle with a coil-on-plug ignition system is exhibiting a misfire, and swapping ignition coils does not move the misfire to a different cylinder, what should be tested NEXT?

A DTC P0505 - Idle Control System Malfunction is present, and the engine is idling erratically. All vacuum lines are intact and correctly connected. What should be the NEXT step?

A vehicle with a turbocharged engine sets a DTC P0234 - Turbocharger/Supercharger Overboost Condition. What should be checked FIRST?

A technician is diagnosing a vehicle with a DTC P0442 - Evaporative Emission Control System Leak Detected (small leak). The gas cap and EVAP lines have been checked and are not the cause. What is the NEXT best step in diagnosis?

A DTC P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) is set shortly after clearing codes on a vehicle. The coolant level is normal, and the vehicle maintains proper operating temperature. What should be the NEXT step in troubleshooting?

When diagnosing a hybrid vehicle that exhibits reduced power and has set a DTC P0A7F - Hybrid Battery Pack Deterioration, which of the following is the MOST appropriate initial diagnostic step?

A vehicle's engine exhibits a condition of running rich under load but operates normally at idle. No DTCs are present. Which of the following is MOST likely causing this issue?

A vehicle with a fully electronic throttle control system is exhibiting a DTC P2135 - Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation. What should be the NEXT step after clearing the code and having it return?

When a vehicle exhibits a P0300 - Random/Multiple Cylinder Misfire Detected code and there is a notable lack of power with no abnormal noises, what should be checked FIRST?

A technician retrieves a DTC P0171 - System Too Lean (Bank 1). After checking for vacuum leaks and finding none, what is the NEXT most likely component to investigate?

During the diagnosis of an engine that will not start, you find that there is no injector pulse. The cam and crank sensors have been replaced, and there is adequate fuel pressure. What is the NEXT logical step?

What should be inspected FIRST when a vehicle equipped with an electronically controlled automatic transmission is setting a P0753 - Shift Solenoid 'A' Electrical code?

A hybrid vehicle sets a DTC P0A80 - Replace Hybrid Battery Pack. Technician A says that individual battery modules should be tested and replaced as necessary. Technician B says that the entire battery pack must be replaced. Who is correct?

A vehicle with a direct fuel injection system has a rough idle and sets a misfire code for cylinder number 2 only when cold. What is MOST likely to be the cause?