Semiconductors & Electronic Switching · Mini Course 08

Semiconductor Fault Diagnosis & Electronic Driver Testing

Investigate an ECU-controlled load without guessing at parts. Compare the command, electrical supply, driver output, and actual load current using simulated meters and waveforms.

10 lessonsVirtual DMM + oscilloscope5 diagnostic casesOffline interactive HTML

Your mission

A vehicle module can command a component without the component actually working. You will learn to separate requested operation, driver command, voltage at the load, and current through the load.

Simulation and shop safety: This is a simplified 12 V, chassis-grounded, resistive-load model, not a vehicle wiring diagram. Follow OEM service procedures, use suitably rated equipment, and isolate power before resistance checks. Never connect a conventional oscilloscope ground clip to B+ or an unidentified/high-voltage point. Do not probe HV propulsion circuits using these exercises.
01Identify command
Did the module intend to turn the load on?
02Verify the path
Can power flow through the load and the driver?
03Verify the outcome
Did the load receive voltage and draw current?

10 guided lessons

Open each lesson, study its example, then mark it complete.

Electronic Driver Workbench

In this simplified low-side circuit, B+ supplies a resistive load. A module-controlled N-channel MOSFET completes the ground path. A PWM command switches the MOSFET on and off repeatedly.

Fuseprotected feedLOAD12 ΩB+ 12 VLoad supplyDrainN-MOSdriverECU PWMGateSource / groundConcept schematic · not a vehicle-specific circuit
MOSFET ON: drain voltage is near ground and load current flows. MOSFET OFF: an intact load pulls the drain toward B+, with almost no load current. The diagram uses idealized switching; real modules may use current sensing, clamps, high-side drivers, diagnostic pull-ups, or multi-stage output circuits.

Configure the healthy circuit

Expected operation

0.99 A
Load current while ON
0.40 A
Average load current
0.10 V
Drain-to-chassis, ON
11.90 V
Voltage across load, ON

ON current ≈ supply ÷ (load R + 0.10 Ω driver R).
Average current ≈ ON current × PWM duty fraction.
Examples assume ideal rectangular PWM and a resistive load.

Virtual DMM & Oscilloscope

Change the simulated circuit state, select a test point, and compare meter readings with the waveform. Start with a known-good baseline before introducing faults.

12.00 V
Virtual meter measurement
40% · 100 Hz
Commanded duty · frequency
Normal
Injected circuit state

An averaging meter reads the time average of an idealized waveform. Real DMM readings depend on meter design, bandwidth, and waveform.

Oscilloscope trace · gate command

Oscilloscope trace · MOSFET drain

Current clamp trace · load current

Two displayed PWM periods. Abrupt edges and stable current are model simplifications; motor coils, solenoids, and protected drivers behave differently.

Fault Injection Lab

Select a known fault, then return to the meter and waveforms to practice identifying its electrical signature. These symptoms apply to this teaching model, not all real vehicle driver designs.

Healthy operation

Investigation path

1. Confirm the requested operation and module command. 2. Check fused load feed. 3. Check driver output while ON and OFF. 4. Compare load voltage to actual current. 5. Verify the fault and repair using service information.

Quick reference: expected signatures

ConditionGate commandDrain when commanded ONCurrent when commanded ON
Healthy5 VNear 0 VNear supply ÷ load R
Open load5 VNear 0 V in this model0 A
Driver fails open5 VNear B+0 A
Driver shorted ON0 or 5 VNear 0 V, even when OFFFlows even when OFF
Missing load feed5 VNear 0 V when ON0 A
Resistive load feed5 VNear 0 V when ONLower than expected
No commanded ON pulse0 VNear B+ through intact load0 A

High-impedance and open-circuit measurements can float on real vehicles. Use an OEM-approved load or targeted tests as appropriate; the model assumes a diagnostic pull-up for an open load’s OFF interval.

The Challenger's Diagnostic Lab

The next five cases hide the failure. You must reveal all three tests before selecting the conclusion supported by the evidence. The cases use the same 12 V resistive load model with the driver commanded ON unless stated otherwise.

0/5 solved

Reveal all three measurements before choosing.

Final Assessment

Answer all five questions. A score of 4/5 passes. Complete the other activities to earn the course badge.