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These 10 free DSD questions are organized by exam domain, so you can see how each part of the Diesel Scanner Diagnostics Certification blueprint is tested. Reveal the answer and explanation under each question.
During a stabilized low-power test, desired boost is 145 kPa gauge, manifold pressure is 225 kPa absolute, and local barometric pressure is 85 kPa absolute. Both pressure readings have been validated. The permitted boost-tracking error for this test is plus or minus 10 kPa. Select the correct interpretation of this pull.
Correct answer: D - 140 kPa gauge; boost tracking is within the permitted range.
Global OBD II communicates normally with a diesel truck's powertrain, but its data list contains no individual wheel speeds. The scan tool's coverage information confirms that its installed manufacturer-specific ABS application supports this exact vehicle. How should the technician obtain the wheel-speed data?
Correct answer: C - Enter the manufacturer-specific ABS application and select its live data.
An EGR functional test is being used to investigate an insufficient-flow fault. Under the specified steady test conditions, opening the valve should reduce measured fresh-air mass flow. The scan tool accepts the command, position feedback follows it, and valve movement is independently verified. Fresh-air mass flow does not change, although that measurement has passed its checks. Which diagnostic direction is now best supported?
Correct answer: D - Check the EGR gas-flow path for a restriction.
A common-rail diesel loses power under load and records P0087, fuel rail/system pressure too low. Requested rail pressure is 120 MPa; actual pressure is 78 MPa, and the pressure-sensor circuit passes its checks. At the same operating point, a gauge at the high-pressure pump inlet reads 180 kPa; the specified supply range is 350-550 kPa. Which fault path deserves investigation before the high-pressure pump is condemned?
Correct answer: B - The low-pressure supply feeding the high-pressure pump.
An engine controller intermittently drops off the network when electrical loads are switched on. Battery voltage stays at 12.6 V. During the dropout, the loaded voltage drop is 0.08 V from battery positive to the controller's supply terminal and 2.4 V from the controller's ground terminal to battery negative. The service limits are 0.20 V for the feed and 0.10 V for the ground return. Which repair should precede another communication test?
Correct answer: B - Repair the controller's ground-return path.
A truck loses power on long grades. The technician wants to distinguish deliberate engine torque limiting from failure to achieve requested boost. The custom list already contains engine speed, accelerator-pedal position, manifold absolute pressure, and barometric pressure. All of the following additional parameters are supported. Which set of four additions most directly separates those explanations?
Correct answer: C - Desired boost, torque-limit status, turbo actuator command, turbo actuator position.
Following wheel-bearing service, a truck with Bendix EC-80 ABS and passive sensors intermittently loses the left-front wheel-speed signal at low speed. With the vehicle secured and the prescribed sensor test setup in place, measurements at the disconnected ECU harness are 2,000 ohms and 0.10 VAC at approximately 0.5 wheel revolution per second. Bendix specifies 1,500-2,500 ohms and AC output above 0.25 VAC for this test. The resistance is acceptable; what does the AC result justify?
Correct answer: A - Inspecting sensor seating, the air gap, and the tone ring at that wheel.
A high-mileage truck completes a service regeneration that meets the specified temperature and duration targets. At the same engine speed and load, DPF differential pressure remains above its service limit. The pressure sensor and sensing tubes pass their checks. Inspection confirms substantial ash accumulation in an intact filter approved for off-vehicle cleaning. What maintenance addresses the remaining restriction?
Correct answer: D - Remove the filter for an approved ash-cleaning procedure.
A transmission is holding a steady commanded gear with no shift in progress. Engine speed is 1,800 rpm, converter turbine speed is 1,500 rpm, and transmission output speed is 750 rpm. The turbine directly drives the transmission gearset, and the converter clutch is commanded released. For this gear, the specified turbine-to-output speed ratio is 1.90-2.10. Which conclusion belongs in the diagnostic record?
Correct answer: B - Ratio 2.00; the commanded gear's speed-ratio check passes.
Two technicians review a J1939 fault for a pressure parameter. One says, 'FMI 3 and FMI 0 both mean the pressure is too high, so they lead to the same diagnosis.' What distinction is being overlooked?
Correct answer: A - FMI 3 identifies high signal voltage; FMI 0 identifies valid data above normal at the most severe level.
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