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newSchoolWorks.com › VoTechWorks › Transportation › Automotive Technology › Capstone Project: Integrated Vehicle Diagnosis, Repair, and Documentation › Lesson 2
TRN-AUTO19-09 · Lesson 2 · 160 clock hours · lab

Hands-On Multi-System Diagnosis and Repair

Objective. The student diagnoses root causes for all prioritized concerns using structured diagnostic strategies, completes all approved repairs to manufacturer specifications, and verifies each repair with the appropriate test or drive cycle before closing the repair order line.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Hands-On Multi-System Diagnosis and Repair

This lab is the practical center of your capstone project. You will diagnose real faults on an assigned shop vehicle, execute all approved repairs to manufacturer specifications, and verify every repair before closing each repair order line. The habits you build here—careful documentation, structured thinking, and disciplined verification—are exactly what ASE A1–A8 and EV L3 examiners expect you to demonstrate on the job.

The Five-Step Diagnostic Process

Every concern, regardless of which system it affects, follows the same five steps:

1. Verify the complaint. Reproduce the customer's described symptom under the same conditions. If you cannot reproduce it, you cannot diagnose it. Note ambient temperature, engine temperature, and operating mode at the time of occurrence.

2. Gather data. Retrieve and record all diagnostic trouble codes (DTCs)—both current and pending—with a scan tool that supports live data and bidirectional control. Pull freeze-frame data for each DTC. Access wiring diagrams, component locations, and OEM specifications in AllData or Mitchell1 before touching a component.

3. Isolate the fault. Use the data to form a hypothesis, then test it. Electrical faults require voltage, resistance, and voltage-drop testing with a calibrated digital volt-ohmmeter (DVOM). Brake concerns require measuring lining thickness with a gauge and checking wheel bearing play with a dial indicator. Cooling or sealing concerns call for a compression or leak-down test. HVAC concerns require manifold gauge pressures and vent temperature measurements. Record every reading in the repair order—not on a scratch pad.

4. Repair. Perform only the approved repair, using OEM torque specifications from the service information. Use a calibrated torque wrench; estimate nothing. Replace fluids with the OEM-specified type and capacity. For brake hydraulic work, bleed the system with a pressure or vacuum bleeder and record the result. For A/C refrigerant work, use an SAE J2788-compliant recovery/recycle/recharge machine and follow EPA Section 609 practices—no venting refrigerant to atmosphere, ever.

5. Verify the fix. This step closes the loop. Run the vehicle through the appropriate OEM drive cycle to confirm all readiness monitors set to 'Ready.' Road-test or lift-test as required. Recheck brake pedal feel. Verify A/C vent temperature meets specification. Capture a post-repair scan tool screenshot and attach it to the repair order. If the verification fails, return to step 2.

Relearns and Service Resets

Many modern vehicles require electronic relearns after component replacement or disconnection. Common examples include throttle body relearn, steering angle sensor (SAS) calibration after alignment or steering work, and TPMS relearn after tire rotation or sensor replacement. Failing to perform required relearns leaves warning lights on and can create new drivability or safety concerns. Perform all relearns through the scan tool before road-testing and document each one on the repair order.

Documentation Standards

Every measurement must be recorded with its units, the OEM specification alongside it, and a pass/fail conclusion. A repair order entry that reads "brake pads OK" is unacceptable. A correct entry reads: "LF brake lining measured 4 mm; OEM minimum 2 mm; within spec." Screenshots from the scan tool, including pre- and post-repair DTC status and readiness monitor status, are required evidence—not optional.

Safety Non-Negotiables

Personal protective equipment (PPE): Safety glasses are required at all times in the shop. Nitrile gloves protect against petroleum products. Chemical-resistant gloves are mandatory when handling brake fluid or refrigerant. If any hybrid or electric vehicle (HEV/EV) work is included in your project, Class 0 insulating gloves rated for high-voltage work are required before contacting any orange-jacketed high-voltage cable or component. Never assume a vehicle is de-energized because the ignition is off.

Lockout/tagout (LOTO): When performing repairs that require disabling the vehicle's ability to start or move unexpectedly—such as brake system work with the vehicle on a lift—apply LOTO procedures per your shop's written policy. Place wheel chocks before lifting.

Refrigerant handling: Refrigerant must never be vented. Use a refrigerant identifier before connecting recovery equipment to verify the system contains the expected refrigerant and is not contaminated. Operate the recovery/recycle/recharge machine according to manufacturer instructions and EPA Section 609 requirements.

Torque compliance: Under-torqued fasteners can loosen and create dangerous failures; over-torqued fasteners can strip threads or crack components. Use a calibrated torque wrench for every critical fastener. Angle-torque (torque-to-yield) procedures require an angle adapter—a conventional torque wrench alone is not sufficient for those fasteners.

Checkpoint and Final Evaluation

Your instructor will conduct a mid-project checkpoint at approximately 80 hours of repair work. Bring your repair order documentation, be prepared to explain the logic behind your test data, and expect one completed repair to be spot-checked for specification compliance. The final evaluation requires every repair order line closed with a recorded verification result, all scan data attached, and zero unaddressed safety violations observed during any lab session. Meeting OEM specification on every measured item, with complete and internally consistent documentation, is the pass standard.

Key terms10

Diagnostic Trouble Code (DTC)A standardized alphanumeric code stored by the vehicle's control module that identifies a detected fault or out-of-range condition in a monitored circuit or system.
Readiness MonitorAn onboard self-test routine run by the ECM to verify that an emission-related system has been checked and is functioning correctly; must show 'Ready' (complete) before an OBD II vehicle can pass an emissions inspection.
Voltage Drop TestA DVOM test performed with current flowing in a circuit to measure resistance-caused voltage loss across a connector, wire, or ground; preferred over resistance-only testing for loaded circuit diagnosis.
Leak-Down TestA cylinder sealing test in which regulated compressed air is introduced through the spark plug port with the piston at TDC; the percentage of air that escapes indicates the condition of rings, valves, and head gasket.
Torque-to-Yield (TTY) FastenerA one-time-use fastener engineered to stretch into its elastic limit during installation; requires an angle-torque procedure and must be replaced rather than reused.
SAE J2788The SAE standard that specifies performance requirements for refrigerant recovery/recycle/recharge machines used in automotive A/C service, including refrigerant purity and charge accuracy.
Steering Angle Sensor (SAS) CalibrationA scan-tool relearn procedure that resets the steering angle sensor's zero reference point after alignment, steering component replacement, or battery disconnection; required for proper electronic stability control operation.
Bidirectional ControlA scan tool feature that allows the technician to command actuators—such as fuel injectors, cooling fans, or ABS solenoids—to operate independently of normal control logic in order to isolate faults.
Class 0 Insulating GlovesRubber insulating gloves rated to protect against voltages up to 1,000 V AC; required PPE when working on or near high-voltage components in hybrid and electric vehicles.
Drive CycleA specific sequence of vehicle operating conditions—speeds, loads, idle periods, and decelerations—defined by the OEM or EPA to allow all OBD II readiness monitors to run and complete after a fault repair or battery disconnect.

Worked examples4

1. A brake lining gauge reads 3 mm on the left-front inboard pad. The OEM specification states the minimum lining thickness is 2 mm and the new-lining thickness is 12 mm. Express the remaining lining as a percentage of usable life consumed.
  1. Step 1 – Identify usable lining range. Usable lining = new thickness − minimum thickness = 12 mm − 2 mm = 10 mm.
  2. Step 2 – Identify remaining usable lining. Remaining usable lining = measured thickness − minimum thickness = 3 mm − 2 mm = 1 mm.
  3. Step 3 – Calculate percentage of usable life consumed. Life consumed = (usable lining used ÷ total usable lining) × 100 = ((10 mm − 1 mm) ÷ 10 mm) × 100 = (9 ÷ 10) × 100 = 90%.
  4. Step 4 – Record on repair order. Entry: 'LF inboard pad measured 3 mm; OEM minimum 2 mm; new 12 mm; 90% of usable life consumed; above OEM minimum—within spec at this time; customer advised.'
Answer: The pad has consumed 90% of its usable life (1 mm of 10 mm usable lining remains). The pad is above the OEM minimum of 2 mm but requires customer notification and near-term replacement.
2. During a voltage-drop test on the starter circuit ground path, the DVOM reads 0.45 V while the engine is cranking. The OEM maximum allowable voltage drop for any ground cable is 0.20 V. How much excess voltage drop exists, and what does this indicate?
  1. Step 1 – Identify the measured value and the specification. Measured drop = 0.45 V; OEM maximum = 0.20 V.
  2. Step 2 – Calculate excess voltage drop. Excess = measured − maximum = 0.45 V − 0.20 V = 0.25 V.
  3. Step 3 – Interpret the result. Any voltage drop across a conductor represents resistance that should not be there; 0.25 V above the limit indicates excessive resistance in the ground cable or its connection—likely a corroded terminal, loose clamp, or damaged cable.
  4. Step 4 – Record and plan repair. Entry: 'Starter ground cable voltage drop 0.45 V under crank load; OEM max 0.20 V; 0.25 V excess—clean and tighten battery negative terminal and engine ground strap; retest after repair.'
Answer: The voltage drop exceeds the OEM maximum by 0.25 V, confirming excessive resistance in the starter ground circuit. The ground cable connections must be cleaned, tightened, or replaced, then retested.
3. A compression test on a four-cylinder engine yields the following readings: cylinder 1 = 165 psi, cylinder 2 = 168 psi, cylinder 3 = 102 psi, cylinder 4 = 160 psi. The OEM specification is 150–175 psi with no more than 25% variation between the highest and lowest cylinder. Determine whether cylinder 3 is within specification.
  1. Step 1 – Confirm range specification. OEM minimum = 150 psi; OEM maximum = 175 psi. Cylinder 3 at 102 psi is below the 150 psi minimum—already a fail on the range test.
  2. Step 2 – Calculate the 25% variation limit. Highest reading = 168 psi. Maximum allowable variation = 25% × 168 psi = 0.25 × 168 = 42 psi.
  3. Step 3 – Calculate actual variation for cylinder 3. Variation = highest − cylinder 3 = 168 psi − 102 psi = 66 psi.
  4. Step 4 – Compare to allowable variation. 66 psi > 42 psi allowable—fails the variation test as well.
  5. Step 5 – Record and plan next step. Entry: 'Cylinder 3 compression 102 psi; OEM 150–175 psi; variation from highest (168 psi) = 66 psi; OEM max variation 42 psi. Both tests fail. Perform leak-down test on cylinder 3 to identify sealing fault (rings, valves, or head gasket).'
Answer: Cylinder 3 fails both the minimum pressure specification (102 psi vs. 150 psi minimum) and the maximum variation specification (66 psi vs. 42 psi maximum allowable). A leak-down test is the required next diagnostic step.
4. After an A/C recharge, the technician verifies vent temperature. The OEM specification states that with ambient temperature at 80 °F, engine at idle, blower on max, and doors closed, center vent temperature should be 40 °F or below. The measured vent temperature is 47 °F. Calculate how many degrees out of specification this reading is and identify the next diagnostic direction.
  1. Step 1 – Identify the specification limit and the measured value. Specification: ≤ 40 °F; Measured: 47 °F.
  2. Step 2 – Calculate the deviation. Deviation = measured − maximum allowable = 47 °F − 40 °F = 7 °F above specification.
  3. Step 3 – Determine that the verification test has failed. The repair is not confirmed; the repair order line cannot be closed.
  4. Step 4 – Identify next diagnostic direction. Check manifold gauge pressures against OEM charge specifications for current ambient temperature; verify refrigerant charge weight is correct; inspect condenser airflow, compressor clutch engagement, and expansion valve or orifice tube operation. Record: 'Post-recharge vent temp 47 °F; OEM ≤ 40 °F at 80 °F ambient; 7 °F out of spec. Verification failed. Returning to diagnosis—checking system pressures and refrigerant charge.'
Answer: The vent temperature is 7 °F above the OEM maximum. The verification test fails; the repair order line must remain open and diagnosis must continue, beginning with system pressure checks and charge weight verification.

The math in this lesson2

Learners compute remaining lining life, compression variation as percent, and vent temperature drop.
7.RP.3N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Work through each concern using a five-step diagnostic process (verify complaint, gather data, isolate fault, repair, verify fix): retrieve and interpret DTCs with the scan tool; access wiring diagrams and component location data in AllData or Mitchell1; perform electrical tests (voltage, resistance, voltage drop), pressure tests, mechanical measurements (brake lining thickness with a gauge, wheel bearing play, belt tension, compression or leak-down as needed), and HVAC performance tests as required by the fault type—recording all data in the repair order. · Execute all approved repairs following OEM torque specifications, using calibrated torque wrenches and, where applicable, angle-torque adapters; replace fluids to OEM type and capacity; perform brake system bleeding using pressure or vacuum bleeder; recharge A/C only with a certified refrigerant recovery/recycle/recharge machine operated under EPA Section 609 practices; reset service reminders and perform required relearns (throttle body, steering angle sensor, TPMS) via scan tool. · After each repair, perform the specified verification test: road-test or lift-test the repaired system, run a drive cycle to confirm DTC readiness monitors set to 'Ready,' recheck brake pedal feel and stopping distance, verify A/C vent temperature meets specification, and capture post-repair scan data screenshots to attach to the repair order as evidence of successful repair.
Materials: Assigned shop vehicle, full tool set (hand tools, torque wrenches, specialty sockets), scan tool with live data and bidirectional control capability, DVOM, lab scope (optional), brake pressure bleeder, refrigerant recovery/recycle/recharge machine (SAE J2788-compliant), refrigerant identifier, vacuum pump, manifold gauge set, compression tester, leak-down tester, micrometer and vernier caliper set, dial indicator, OEM service information via AllData/Mitchell1, parts (ordered by student through instructor approval), safety glasses, nitrile gloves, chemical-resistant gloves for brake fluid/refrigerant, Class 0 insulating gloves if HEV/EV work is included, ASE A1–A8 and EV L3 task lists
Check: Instructor conducts a mid-project checkpoint at approximately 80 hours of repair work: reviews documented test data for logic and accuracy, spot-checks one completed repair for torque and specification compliance, and verifies scan tool verification screenshots are attached. Final check: all repair order lines closed with a verification test result recorded; no safety non-compliance observed during any lab session. Pass standard: all repairs within OEM specification (measured and documented); repair order data complete and internally consistent; zero unaddressed safety violations.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

ASE A8 – Engine Performance
1. A technician retrieves a pending DTC for an oxygen sensor heater circuit on a vehicle that was just purchased used. What should the technician do FIRST before replacing the oxygen sensor?
ASE A6 – Electrical/Electronic Systems
2. During a voltage-drop test on a headlight ground circuit with the lights on, the DVOM reads 0.6 V. Which condition does this MOST likely indicate?
ASE A1 – Engine Repair
3. A cylinder leak-down test on cylinder 4 shows 35% leakage, and the technician hears air escaping from the throttle body air intake. What does this finding MOST likely indicate?
ASE A4 – Steering and Suspension
4. After replacing a steering rack on a vehicle equipped with electronic stability control, the technician must perform which of the following relearn procedures before returning the vehicle to the customer?
ASE A7 – Heating and Air Conditioning
5. Which EPA regulation governs the recovery, recycling, and recharge of mobile air conditioning refrigerant?
ASE EV L3 – Electric Vehicle
6. A technician is about to replace a high-voltage drive motor cable on a hybrid electric vehicle. Which PPE item is required that would NOT be required for a conventional brake job?
ASE A5 – Brakes
7. After completing a brake fluid flush and bleeding on all four corners, which of the following is the BEST method to verify the repair before closing the repair order?
ASE A1 – Engine Repair
8. A technician installs a new cylinder head and the OEM service information specifies torquing the head bolts to 30 ft-lb, then rotating each bolt an additional 90 degrees. What type of fastener procedure is described, and what special tool is required?
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