Workshop Safety and PPE
Not publishedof exam
Circuits, Wiring and Fusing
Not publishedof exam
Battery, Charging and Starting
Not publishedof exam
Lighting and Body Electrical
Not publishedof exam
Sensors, ECU and Networks
Not publishedof exam
Test Equipment and Diagnostics
Not publishedof exam
Quick Facts
- Owner
- PACC / Takamol / MHRSD
- Platform
- pacc.sa
- Occupation code
- SSCO 9214013
- Format
- Computer test plus practical
- Time limit
- Maximum 120 minutes
- Questions
- Not published
- Passing score
- Not published
- Domain weights
- Not published
- Attempts
- Up to 3, each paid
- Fee outside KSA
- USD 50 per attempt
- Fee inside KSA
- SAR 540.50 per attempt
- Validity
- 5 years with practical
- Vehicle system
- 12 V negative earth
Hazard Response Picker
- Energised electrical fire→CO2 or dry powder(Isolate supply)
- Acid in the eyes→Flush 15 minutes(Never neutralise)
- Battery gassing hard→Ventilate, kill all sparks
- Working near an airbag→Wait for capacitor discharge
- Orange cable in reach→Stop, call HV technician
- Handling a bare module→Earthed wrist strap
PPE and Isolation
- 12 V burn risk
- Arc and weld, not shock
- Rings and watches
- Metal bridges to earth
- Disconnect order
- Negative first, positive last
- Reconnect order
- Positive first, negative last
- Lockout tagout
- Only the fitter unlocks
- Charging battery
- Releases explosive hydrogen gas
- Acid in the eyes
- Flush 15 minutes, seek help
- Electrical fire
- CO2 or dry powder
- Airbag work
- Wait for capacitor discharge
Battery Hazards
- Before moving clamps
- Switch the charger off
- Charging bay
- Ventilate, keep sparks away
- Spilled acid
- Neutralise with baking soda
- Acid on skin
- Flush with water only
- Jump start last clamp
- Engine earth, away from battery
- Lifting a battery
- Use a carry strap
- Damaged or bulging case
- Do not charge it
- Gulf heat
- Shortens battery service life
High Voltage Safety
- Orange cable
- High voltage, do not touch
- Automotive high voltage
- Over 30 VAC or 60 VDC
- Voltage class A
- Up to 60 V DC
- Voltage class B
- Above 60 V DC
- Governing standard
- ISO 6469-3 electrical safety
- Who may work
- Trained HV technicians only
Relay Pin Order
30 feeds, 85 and 86 coil, 87 out
30: battery feed85: coil earth86: coil supply87: normally open87a: normally closed
Series vs Parallel
Series
- One path only
- Current stays same
- Resistances add up
Parallel
- Several paths
- Voltage stays same
- Total below smallest
One path versus many
Circuit Fault Picker
- Fuse blows immediately→Short to ground
- Load runs on its own→Short to power
- No voltage at load→Open circuit
- Dim or slow operation→High resistance
- Works cold, fails hot→Thermal intermittent
- Several circuits affected→Shared earth or feed
Ohm's Law and Power
- Ohm's law
- V = I x R
- Current
- I = V / R
- Resistance
- R = V / I
- Power
- P = V x I
- Power from current
- P = I squared R
- Series resistance
- Add the resistors up
- Parallel resistance
- Less than smallest resistor
- Series current
- Same at every point
- Parallel voltage
- Same across each branch
- Kirchhoff current rule
- In equals out
Ohm's Law Triangle
V equals I times R
I = V / RR = V / IP = V x I
Open vs Short
Open
- No current flows
- Fuse stays good
- Load simply dead
Short
- Excess current flows
- Fuse blows
- Wire can burn
Dead load versus blown fuse
Circuit Fault Types
- Open circuit
- No current, load dead
- Short to ground
- Fuse blows at once
- Short to power
- Load on unexpectedly
- High resistance
- Dim, slow, running hot
- Parasitic draw
- Key-off current drain
- Intermittent fault
- Comes and goes
- Bad earth
- Several circuits misbehave
Terminal 87 vs 87a
87
- Normally open
- Live when energised
- Load switches on
87a
- Normally closed
- Live when resting
- Load switches off
Energised on versus resting on
DIN 72552 Terminals
- 30
- Battery positive, unswitched
- 31
- Earth, battery negative
- 15
- Switched positive, ignition on
- 50
- Starter solenoid trigger
- 54
- Stop lamp
- 55
- Fog lamp
- 56a
- Main beam
- 56b
- Dipped beam
- 58
- Side and tail lamps
- 61
- Charge warning lamp
- 49
- Flasher unit input
- 49a
- Flasher unit output
- B+
- Alternator battery output
- D+
- Alternator excitation output
- W
- Alternator speed signal
- L and R
- Left and right indicators
Relay Pin Map
- 85
- Coil earth side
- 86
- Coil supply side
- 30
- Common contact feed
- 87
- Normally open output
- 87a
- Normally closed output
- Coil diode
- Cathode goes to 86
- Diode fitted
- Coil polarity now matters
- Why a relay
- Small current switches large
Blade Fuse Colours
- 2 A
- Grey
- 3 A
- Violet
- 5 A
- Tan
- 7.5 A
- Brown
- 10 A
- Red
- 15 A
- Blue
- 20 A
- Yellow
- 25 A
- Clear or natural
- 30 A
- Green
- 40 A
- Orange
Wire Gauge Sizes
- Lower AWG number
- Thicker conductor
- 20 AWG
- About 0.5 mm2
- 18 AWG
- About 0.8 mm2
- 16 AWG
- About 1.3 mm2
- 14 AWG
- About 2.1 mm2
- 12 AWG
- About 3.3 mm2
- 10 AWG
- About 5.3 mm2
- Choosing gauge
- Current and voltage drop
- Undersized repair wire
- Drops voltage, runs hot
Harness Repair Rules
- Preferred joint
- Correctly crimped terminal
- Solder in engine bay
- Stiff joint cracks
- Sealing a repair
- Adhesive-lined heat shrink
- Multiple splices
- Stagger along the loom
- After any repair
- Restore clips and routing
- Testing a live plug
- Back-probe, never pierce
- Connector cleaning
- Contact cleaner, no abrasives
State of Charge
12.6 full, 12.2 half, 11.9 flat
12.65 V: 100 percent12.24 V: 50 percent11.89 V: flatRest four hours
CCA vs Reserve Capacity
CCA
- Cold cranking burst
- 30 seconds
- Above 7.2 V
Reserve capacity
- Minutes at 25 A
- Down to 10.5 V
- Alternator dead
Start it versus run it
No Crank Diagnosis
- Nothing happens at all→Battery, earths, main feed
- Rapid clicking→Battery or connections(Voltage collapses)
- One solid click→Solenoid or starter(Contacts or motor)
- Slow crank, high draw→Drag or internal short
- Slow crank, low draw→Cables, joints, earths
- Cranks in neutral only→Park neutral switch
- Cranks but no start→Immobiliser, fuel or spark
Battery Ratings
- CCA
- Cranking amps at -18 C
- CCA cut-off
- Stays above 7.2 V
- Reserve capacity
- Minutes at 25 A
- Reserve cut-off
- Down to 10.5 V
- Amp hours
- Capacity over 20 hours
- Cell voltage
- 2.1 V nominal
- 12 V battery
- Six cells in series
- Full specific gravity
- About 1.265
Jump Start Order
Dead plus, good plus, good minus, engine earth
Last clamp: engine earthNever the flat negativeRemove in reverse order
AGM vs Flooded
AGM
- Sealed, valve regulated
- No water top-up
- No equalise charge
Flooded
- Vented cells
- Water can be added
- Equalise charge allowed
Sealed needs controlled charging
Charging Fault Picker
- Below 13.5 V running→Alternator or field circuit
- Above 15 V running→Regulator overcharging
- AC ripple over limit→Rectifier diode failed
- Output fine, battery flat→Earth path voltage drop
- Voltage keeps changing→Smart charging strategy(Check scan data)
- Charge lamp stays lit→D+ or excitation circuit
State of Charge Voltage
- 12.65 V
- 100 percent charged
- 12.45 V
- 75 percent charged
- 12.24 V
- 50 percent charged
- 12.06 V
- 25 percent charged
- 11.89 V
- Discharged
- Rest before reading
- Four hours minimum
- Surface charge
- Load briefly, then read
- Load test
- Half CCA, 15 seconds
- Load test pass
- 9.6 V at 21 C
- Conductance tester
- Works when partly discharged
Charging System
- Typical output
- 13.5 to 14.5 V
- Rectifier bridge
- Three-phase AC to DC
- Voltage regulator
- Controls rotor field current
- AC ripple limit
- Under 0.5 V AC
- High AC ripple
- Failed rectifier diode
- Temperature compensation
- Minus 3 mV per cell
- Hot battery
- Needs lower charging voltage
- Smart charging
- Voltage varies by design
- Charge lamp lit
- Charging system not working
- Good output, flat battery
- Check the earth path
Starting System
- Pull-in winding
- Throws pinion, closes contacts
- Hold-in winding
- Keeps contacts closed
- Rapid clicking
- Supply collapses under load
- High draw, slow crank
- Drag or internal short
- Low draw, slow crank
- High resistance in circuit
- Overrunning clutch
- Stops engine back-driving starter
- Park neutral switch
- Blocks crank unless parked
- Parasitic draw target
- Under about 50 mA
- Module sleep time
- 20 to 60 minutes
Lighting Terminals
56 head, 58 side, 54 stop, 55 fog
56a: main beam56b: dipped beam58: side and tail54: stop lamp
Lamp Fault Picker
- One lamp dead→Bulb, socket or earth
- All lamps dead→Fuse, switch or module
- Warning after bulb change→Wrong bulb wattage
- Dim yellow output→Corroded earth point
- Poor beam after LED→Reflector mismatch
Lamp and Beam Basics
- H4 bulb
- Twin filament, main and dip
- H7 bulb
- Single filament, one beam
- HID lamp
- Needs ballast and igniter
- LED in halogen reflector
- Scatters, ruins beam cutoff
- PWM dimming
- On-time ratio sets brightness
- Meter on PWM
- Shows misleading average voltage
- Bulb outage warning
- Module measures lamp current
- Wrong wattage bulb
- Triggers false outage warning
Body Electrical Control
- Body control module
- Drives lamps and accessories
- Dash switch role
- Low-current input signal
- Dead lamp circuit
- Can be a module
- Shared earth point
- One fault, many symptoms
- Window from master only
- Door switch or wiring
- Accessory supply
- Own fused circuit only
- Amplifier power lead
- Fuse close to battery
Inductive vs Hall
Inductive
- Two wires
- Generates own AC
- Amplitude rises with speed
Hall
- Three wires
- Needs a supply
- Square wave, fixed amplitude
Self-powered versus supplied
Network Fault Picker
- One module silent→Its power and earth
- All modules silent→Bus wiring or termination
- Resistance not 60 ohms→Termination or bus fault
- Several sensors implausible→Shared 5 V reference
- New module fitted→Program and code it
Sensor Types
- Reference supply
- Typically 5 volts
- Coolant and air temp
- NTC thermistor
- NTC behaviour
- Hotter means lower resistance
- Throttle and MAP
- Three-wire, 0.5 to 4.5 V
- Narrowband oxygen
- Switches lean and rich
- Stoichiometric point
- About 450 mV
- Wideband oxygen
- Read by pump current
- Inductive crank sensor
- Two-wire, makes own AC
- Hall sensor
- Three-wire, square wave
- Knock sensor
- Piezoelectric vibration signal
Vehicle Networks
- High-speed CAN
- ISO 11898-2, twisted pair
- Powertrain CAN speed
- Commonly 500 kbit/s
- Low-speed CAN
- ISO 11898-3, 125 kbit/s
- Termination
- 120 ohm at each end
- Bus resistance check
- About 60 ohms, ignition off
- CAN High dominant
- Rises toward 3.5 V
- CAN Low dominant
- Falls toward 1.5 V
- LIN bus
- Single wire, 20 kbit/s
- FlexRay
- 10 Mbit/s, chassis control
- One module missing
- Its power, earth, branch
- Many modules missing
- Bus wiring or termination
ECU Service Rules
- New module fitted
- Program and code it
- Stored adaptations
- Reset after part change
- Shared 5 V reference
- One short affects many
- Immobiliser
- Module must match vehicle
- During coding
- Hold supply voltage steady
- Handling a module
- Earthed wrist strap
Voltage Drop Limits
0.2 wire, 0.3 switch, 0.1 earth
Cable: 0.2 VSwitch: 0.3 VEarth: 0.1 VTest under load
Voltage Drop vs Resistance
Voltage drop
- Circuit under load
- Finds weak joints
- Real operating condition
Resistance
- Circuit dead
- Component isolated
- Can pass falsely
Loaded truth versus dead reading
Test Tool Picker
- Reading starter current→Clamp meter(Circuit stays intact)
- Chasing an intermittent→Oscilloscope(Shows dropouts)
- Suspect bad connection→Voltage drop test(Under load)
- Checking a PWM output→Duty cycle mode
- Module output circuit→High-impedance meter(Never a test lamp)
- Judging battery condition→Conductance tester
- Finding key-off drain→Ammeter in series
Meter Modes
- DC volts
- Parallel across the component
- Amps
- In series, move lead
- Ohms
- Power off, component isolated
- Continuity
- Finds breaks in wire
- Duty cycle
- Reads PWM on-time
- Clamp meter
- High current, circuit intact
- Oscilloscope
- Shows the signal over time
- Test lamp
- Power circuits only
Circuit vs Rationality Code
Circuit code
- Outside electrical limits
- Open or shorted
- Suspect the wiring
Rationality code
- Value electrically legal
- Disagrees with others
- Suspect drifting sensor
Wiring versus drifting sensor
Voltage Drop Limits
- Test condition
- Circuit loaded and working
- Across a cable
- 0.2 V maximum
- Across a switch
- 0.3 V maximum
- At an earth point
- 0.1 V maximum
- Whole starter circuit
- 0.2 to 0.5 V
- Clean connection
- Near zero drop
- Named standard
- SAE J541 starter circuits
Test Lamp vs Multimeter
Test lamp
- Draws real current
- Damages module drivers
- Power circuits only
Digital multimeter
- High impedance
- Safe on modules
- Reads exact value
Load versus safe measurement
Scan Tool Data
- Stored DTC
- Confirmed fault in memory
- Pending DTC
- Seen this drive cycle
- Permanent DTC
- Clears only after repair
- Freeze frame
- Conditions when code set
- Live data
- What sensors report now
- Codes versus data
- Area, then present fault
- Bidirectional test
- Command the actuator directly
DTC Code Format
- P
- Powertrain
- B
- Body
- C
- Chassis
- U
- Network communication
- Second character 0
- Generic, SAE defined
- Second character 1
- Manufacturer specific
- Circuit code
- Outside electrical limits
- Rationality code
- Legal value, illogical reading
OBD-II Connector Pins
- Pin 16
- Battery positive, unswitched
- Pin 4
- Chassis ground
- Pin 5
- Signal ground
- Pin 6
- CAN High
- Pin 14
- CAN Low
- Pin 7
- K-line, ISO 9141
- Connector location
- Within the driver's reach
Common Traps
Fuse protects the wire
It guards the harness ≠ Not the load device
Coil versus contacts
85 and 86 are coil ≠ 30 and 87 carry load
Resting volts versus load
Surface charge reads high ≠ Load test finds truth
Ohms versus voltage drop
Dead resistance can pass ≠ Loaded drop reveals fault
Codes do not name parts
A code names a circuit ≠ Live data confirms it
Charging voltage is not fixed
Smart systems vary output ≠ Judge against maker strategy
Bulb fits, beam fails
LED fits the socket ≠ Reflector still expects filament
One module versus the bus
One silent means branch ≠ All silent means bus
12 volts is not harmless
Shock risk is low ≠ Short circuit energy high
Bigger fuse is not a fix
Wire becomes the fuse ≠ Find the real fault
Last Minute
- 1.Weights and pass mark: not published
- 2.Relay: 30 feed, 87 out
- 3.85 and 86 are coil
- 4.Fuse protects wire, not load
- 5.Lower AWG number, thicker wire
- 6.12.65 V rested equals full
- 7.Load test: 9.6 V minimum
- 8.Charging: 13.5 to 14.5 V
- 9.AC ripple under 0.5 V
- 10.Drop: 0.2 wire, 0.3 switch
- 11.CAN termination reads 60 ohms
- 12.NTC: hotter means lower resistance
- 13.Orange cable equals high voltage
- 14.Negative off first, on last
- 15.Never test lamp on modules
- 16.Rationality code: sensor has drifted
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