141 Questions
What is done when an axle wheel bearing has a blue discolouration?
Replace wheel bearing and increase bearing end play
To ensure accuracy of a digital multimeter, what is done to ensure its test lead resistance does not 0.2 OHMS?
Connect the positive and the negative leads
Where is information regarding the vehicle VIN, Make and model found?
Inside driver’s door B pillar
What is done when preparing to weld on a vehicle?
Disconnect the control modules and the negative cable from the battery
What is the procedure to install a fastener using thread locking compound?
Clean the threads, apply compound then torque to manufacturers specifications
What PPE is required when using a bench grinder?
Hearing and eye protection
A safety stand is missing its capacity reading tag. What is done?
Have safety stand tested and recertified
What is used to clean up an oil spill on the shop floor?
Absorbent pads
When removing a transmission with a transmission jack, what is done to secure the load
secure a ratchet strap around the output shaft
When replacing a VGT actuator, what are the steps to complete the installation?turbo sector
Position the turbo sector shaft to the install position, use scan tool to position actuator, then perform calibration after assembly
What is done to verify an air in fuel problem?
Install a clear hose after the lift pump
What is the cause of a hard start in a HEUI fuel injected engine?actuation
Low oil actuation pressure
During operation of a cooling system, it is found that the temperature is NOT rising above 88C (190F). What is the cause
Thermostat failed open
What is the result of a restricted exhaust system?
The engine operating temperature increases
A truck comes in for service. An engine cooling fan is running continuously.What is checked?
Air conditioning high pressure switch, coolant temperature sensor and intake temperature sensor
Pressure is found in the DEF lines after the ignition is shut off. What is done?
Perform a computer override test and follow the troubleshooting tree to repair the faulty component.
An engine compression brake is weak and the engine warning light is illuminated. what is the cause?
one of the engine compression brakes solid circuits is open
What is done when removing multiple compression brake heads at once?
Mark the brake heads and then reinstall in the original location
What is done to confirm correct operation of a DEF pump?
check pump flow, fluid level and spray pattern
What is the procedure to replace a broken piston cooling nozzle?
drain oil, remove oil pan, replace damaged nozzle, then clean Supply gallery
The inlet Knox sensor is reading higher than normal. What is the cause?
EGR valve stuck open
What is the procedure to collect an oil sample?
warm up engine, remove oil drain plug, then collect the oil sample halfway through the oil drain.
The engine is doing frequent regenerations and there is no check engine light visible. What is the cause?differential
stuck in range DPF differential pressure sensor
What are the steps to install an oil pan on a truck?
Clean meeting surfaces, clean inside the pan, install gasket on pan, apply sealant to seams, position pan, install bolts, then torque
Since new, an engine has excessive oil consuption. What is the cause?
worn oil control rings
What is the procedure to replace a water pump?housing
b. Drain the coolant, remove the accessory drive belt, remove the water pump cartridge, inspect the housing, install a new water pump cartridge, reinstall the accessory drive belt, then fill the cooling system
What is the cause of a high rate of fuel return measured at the cylinder head return gallery in a high pressure common rail system
Leaking high pressure injector connector
What is done to inspect an exhaust system
Inspect the system for soot leaks, routing and supports
What is the procedure to replace a real sensor in a high pressure common rail system?
d. Bleed off the rail pressure then change the sensor
What is the procedure to replace a cooling system filter?
allow the system to cool, close the shut-off valve, remove the filter, install new filter, then open the shutoff valve.
What is done after a major turbocharger failure?
a. check the air Inlet and exhaust system for contamination, standing oil and integrity
Valve clearance becomes tighter between adjustments. what is the cause?
c. The valve seat is worn.
What is the procedure to confirm slow buildup time for an air brake system?
b. Start engine and run at idle, monitor dashboard air pressure gauges, then confirm that the system pressurizes from 50 psi to 90 PSI in 3 minutes or less
The rear wheels of a hydraulic brake system are locking up during hard application. What is the cause?
c. Defective proportioning valve
What is done to release the stored energy when replacing the quick release valve on a secondary air system?
b. Drain all air system tanks to 0 psi
How is S-cam bushing clearance checked?
b. By releasing park brake, then using dial indicator to measure radial play
What will prevent an active ABS after replacing a wheel seal?
a. Pushing the sensor in until it contacts the tone ring.
What is the procedure to remove the spring the chamber on an air brake system?
a. Chock wheels, release park brake, back off service brake, cage power spring,apply park brake, then remove spring chamber
The primary and secondary brake systems of a truck are at normal operating pressures. The primary brake system applies but the secondary brake system does NOT. What is the cause?quick
b. Faulty quick- release valve
What is checked after installing a new rotor?
d. Lateral run out
A truck with a hydraulic brake system pulls to one side during braking. What is the cause?
c. Seized caliper piston
The spring brakes are slow to apply. What is the cause?tractor prot
c. Leaking tractor protection valve
What is done when compressing a hydraulic brake caliper with ABS?
a. Open bleeder screw, then compress caliper piston
A steering axle brake line is cracked. What is done?
b. Replace with a DOT certified rubber hose, then check for leaks
What is done to increase system air pressure?
b. Adjust governor by turning screw clockwise, then verify pressure with master gauge
During a chuff test one chuff is not audible and no active ABS code is present. What is the cause
d. Defective modulator
The primary air gauge reads 120 PSi and the secondary air gauge reads 90 psi at cut-out pressure on a truck dashboard. What is done to verify the accuracy of the air gauge pressure indicators?
b. Install an air pressure gauge at air supply tank and air pressure gauge at secondary air tank
A truck’s air brakes operate normally. When a trailer is connected, the brakes are weak. What is the cause?
b. A faulty tractor protection valve
What causes a 76.2-mm (3in) brake stroke?
a. Push rod length too long
Air leaks out of the treadle valve exhaust port when the hand brake is applied. What is the cause?
b. Faulty 2-way check valve
A truck rides below the height range specified by the manufacturer. What is done to correct the ride height?
d. Chock wheels, release parking brake, normalize suspension, measure at specified location, then adjust levelers to attain specified height
When applying the service air brake, the push rod angle is over 90*. What is done?
c. Measure push rod length
What is the first step when bleeding a hydraulic brake system
b. Bleed the wheel furthest from the master cylinder
What is the procedure to perform a battery load test with a carbon pile load tester?
b. Remove surface charge, load test at half the cold cranking amps for 15 seconds.
On a multi-coil gasoline engine, a miss is discovered on cylinder 4. What is done to test the high voltage system?
a. Swap coils between cylinders and verify the problem follows.
What is the procedure to clean electrolyte from a battery case
a. Wash the battery with a mixture of baking soda and water
Voltage drop across a fuse is 12.7V. What is done?
a. Remove and replace fuse
There is a high voltage drop across the alternator output cable. What is the procedure to replace the cable
b. Disconnect the negative cable at the battery and replace alternator output cable
Refer to figure 47. The 15A fuse is blown. What is the cause
d. The A/C electromagnetic clutch coil is shorted
After converting a unit from incandescent bulbs to LED, the turn signal lights blink rapidly. How is this corrected?
c. By installing a digital flasher in the signal circuit
What is the cause of a swollen wire
a. High Amperage draw
What is done when installing a replacement SRS ECU?
b. Avoid touching pins to prevent damage to the ECU from static discharge
What is the cause of a slowly discharging battery over 36 to 48 hours?
a. Corroded battery connections
Refer to Figure 60. A 250 W inverter is located 60 ft from the 12.7 V batteries. What size supply wire is used?
c. 10 Ga
When performing a tune up on a coil on plug gasoline engine, which components are replaced?
c. Spark plugs, ignition coil(s) and fuel filter
What service is required to prevent a low charging condition?
d. Measure output amperage, visually inspect belts, check for corroded connections to batteries, then check voltage drop across cables
A unit will not crank. When testing, the positive terminal at the starter has 12 V, and 8 V to the S terminal. What is tested next? positive
b. Voltage drop on the positive battery cable
What is the procedure to replace a sensor connector?
c. Remove the wires from the body, remove pins from the wires, remove seal from the wires, install new seals, install new pins, then install into new body
A unit comes in with an excessively hot alternator. What is done to diagnose the problem?
a. Check belt tension, check for bearing drag, check for output amperage, then check for damaged cooling fins
What are the steps to replace data link wires?
b. Twist the wire 2.5 times per inch and select the wire gauge as per manufacturer’s specification.
starter circuit engages. There is 12 V delivered to the starter motor, and 0V at the ground cable. The engine does NOT crank. What is the cause?
b. A short circuit within the motor
Refer to figure 57. The master lighting switch is turned to clearance/marker position and the left headlight also comes on. What is the problem?
c. Short to power at pin 87a of the truck clearance/marker light relay
A slow engine cracking condition is observed. What is done to measure the voltage drop across the negative starter cable?
d. Turn off battery disconnect switch, connect voltmeter to both ends of the starter ground cable, then crank engine while measuring voltage
When checking a 3-wire sensor, the operating range is high. What is the cause?
c. Signal wire shorted to positive voltage
Refer to Figure 50. The splice joint had a 10 V drop. What is the cause?
d. Dome light is dim
A starter is being bench tested. When voltage is removed, the solenoid remains engaged. What is replaced?
b. Hold-in windings
- Oil in differential housing is leaking out of the axles and pinions at the same time. What
is the cause?
a. A plugged breather vent
A new clutch has been installed but will NOT disengage. What is the cause?
c. Disc is installed backwards
What is the procedure to check for fault codes on an automated transmission?
c. Connect service tool, Open OEM software, scan for active and inactive faults, diagnose as necessary, then clear faults once repaired
The manual transmission oil is milky. What is done?
b. Take a sample, drain then refill with new oil
What is done before removing an axle from a differential that is equipped with an axle lock?
b. Place the axle in the lock position
A 6-speed manual transmission becomes locked in gear. What is the cause?
c. Twisted main shaft
The shift selector displays of an automated transmission is flashing “N” (neutral). What is the result?
c. Transmission will not shift
What is the procedure to adjust shift linkage?
d. Put the cab selector in neutral, disconnect the shift cable at the transmission, move the transmission lever to neutral, then adjust the cable
A speedometer malfunctions during the operation of a vehicle. What is the cause?output
d. Transmission output speed sensor has failed
What is the procedure to install a clutch assembly onto a flywheel
d. Insert the pilot shaft in the clutch assembly, attach assembly to flywheel, torque bolts, then remove the pilot shaft
The auxiliary section of an automatic transmission shifts slowly. What is the cause?
b. Low air pressure from air regulator
A clutch release bearing is over greased. What is the result?
c. Clutch disc is contaminated resulting in slippage
An electric drivetrain retarder is working intermittently. What is the cause?
a. A short in the retarder harness
There is a leak at the output shaft area of a truck with an automated transmission. What is done after removing the output shaft yolk?
d. Remove seal, inspect seal bore, then install new seal
During disassembly of an automatic transmission, which components are inspected for wear?
b. Clutch discs, planetary gears and transmission case
A U-joint only greases from 2 caps. What is done?
b. Replace u-joint and grease
What is done after installing an auxiliary section on a 10 speed manual transmission?
d. Check output shaft endplay
A constant noise varies with road speed. What is the cause?
c. Worn U-joint
The wheel rim has turned on a spoke hub. What is done?
c. Disassemble, inspect, replace components as required, ressemble wheel, then check run-out
What is inspected before performing a front-end alignment?
b. Tire pressure, wheel bearings, and suspension components
What is done to repair a broken spring pack?
d. Replace both spring packs on the same axle
What is the procedure to install a hub piloted steer wheel?
c. Raise wheels, tighten nuts in a criss-cross pattern, lower wheels, then torque
Which tool is used to measure trailer king pin wear?
d. Go/No-Go gauge
What is the procedure to install a steel and aluminum wheel combination?
d. Install teflon spacer between wheels, then torque
What is considered when replacing a fifth wheel riser
c. Load range and riser height
During an inspection, loose jaws are found on a fifth wheel. What is done?
b. Replace jaws and pins on the fifth wheel
What is the procedure to measure radial King pin play?
b. Raise the vehicle, install dial indicator magnetic base on the I-beam, then measure horizontal movement between the knuckle and axle
What is the cause of rust streaks on a frame rail?
d. Loose cross member fastener
What is the first adjustment made during a front-end alignment?
d. Toe
When traveling straight forward, the vehicle’s steering wheel is in an off-centered condition. What is the cause?
b. Bent steering shaft
A steering wheel is binding during operation on rough roads. What is the cause?
b. Seized steering shaft U-joint
On a bottom dump trailer, an air bag is torn from the pedestal. What is the cause?
d. A worn out beam bushing
What is the next step to adjust the air suspension ride height after blocking the wheels
a. Release the brakes
An oil leak is found at the hub seal. What is the cause?
a. Loose wheel bearing
A truck has a driveline vibration. What is the cause?
b. Out of phase drive shaft
What is the procedure to determine that a set of tandem axles are parallel to each other?
a. Block the wheels, release the brakes, check the ride height, then compare the center on each side using a trammel bar.
When reinforcing a frame, how is the reinforcement material attached?
a. By cutting material ends at 45* and bolting to web
- During operation, play is noticed between trailer and fifth wheel. What is the cause?
a. Lock-jaws out of adjustment
- During inspection, a drive axle flange gasket is leaking. What is the cause?
a. Loose axle studs
- A cab door is NOT sealing. What is done?
a. Adjust door striker in
- What is used to lubricate seat sliders?
d. White lithium grease
A vehicle information door tag is damaged. What is done?
c. Contact OEM for replacement, then install on door frame
During operation, a power window stops halfway up. What is done?
c. Too much friction in the window track
Cruise control is NOT functioning. Which components are checked?
b. Clutch switch, brake switch and cruise control switch
Excessive cab bounce is noticed. What is the cause?
a. Leaking cab shocks
What is done to repair trailer landing legs that move in opposite directions following a rebuild
b. Open gear box cover, flip idler gear and reassemble
Given the following temperature settings and readings on a multi-temperature heating and refrigeration unit
-Zone 1 temperature setting: -2* C
What is the procedure to repair a trailer with a tire scrubbing condition
d. Repair worn suspension bushings and realign
On a trailer heating/refrigeration power unit, corrosion is found on the starter cable. What is done?
a. Disconnect battery, disconnect starter cable, remove corrosion, apply dielectric grease, then reconnect starter cable
An aluminum trailer frame rail shows corrosion at a bolt hole. What is the cause?
a. Fastener had been replaced with a steel fastener
After a cross-shaft repair, a trailer is NOT level when sitting on landing gear. What is the procedure to correct this?
d. Support and level trailer, then re-time the landing gear legs
What is done after a major compressor failure of an orifice tube type air conditioning system?
b. Replace the compressor, replace the accumulator, then clean and inspect the orifice tube
When servicing an air conditioning system, What is done first?
a. Recover refrigerant
On a cold start, the cab heater takes an excessive amount of time to warm up. What is the cause
b. Engine thermostat is stuck open
A heating and refrigeration unit has failed in the pre-trip mode and engine has shut down. What is the cause?
b. Leaking fuel tank at the mounting straps
What control heater vent temperature?
c. Coolant flow control valve
The pressures in a blended HVAC system are sufficient, but the vent temperatures are higher than specifications. What is the cause?
d. The blend air re-circulating control door is malfunctioning
A system has a low refrigerant charge, but the air conditioning system is still cooling. What is the result?
a. Shorter than normal compressor run time
When Switching the climate control from the floor to the defrost setting, airflow continues to blow from the floor vents. What is the cause?
a. A faulty blend door actuator
When replacing the blower motor, the heater core has over 25% of the surface blocked by flattened fins. What is done?
b. Straighten fins with fin comb
What is used to check for leaks after servicing an air conditioning system?
c. Nitrogen
A bucket truck has a hydraulic line rupture. The bucket is extended and will not retract. What is done to repair the hydraulic line?
d. Replace damaged line, fully retract and cycle cylinders, top up reservoir, then return to operation
When disassembling a hydraulic pump with an integrated relief valve, the relief valve seat is damaged. How is this repaired?
c. Replace pump spool and relief valve as a unit
A hydraulic gear pump is rated for 35 GPM. On inspection, it is working at 83% efficiency. What is the actual flow rate?
b. 29 GPM
Refer to figure 65. The lift gate fails to hold a load when the motor is off, and the motor spins backwards as the load lowers. Which part is changed to repair this problem?
a. Check valve at port A
Study Notes
Axle Wheel Bearing
- A blue discoloration on an axle wheel bearing requires replacement.
Digital Multimeter
- To ensure accuracy, test lead resistance should be checked to ensure it is not exceeding 0.2 OHMS.
Vehicle Information
- Vehicle VIN, make, and model information can be found on the vehicle.
Welding Preparation
- Before welding on a vehicle, the area should be cleaned and prepared.
Fastener Installation
- When installing a fastener using thread locking compound, the instructions on the compound should be followed.
PPE
- When using a bench grinder, safety glasses and a dust mask are required.
Safety Stand
- If a safety stand is missing its capacity reading tag, it should be replaced.
Oil Spill
- An oil spill on the shop floor should be cleaned up immediately.
Transmission Removal
- When removing a transmission with a transmission jack, the load should be secured.
VGT Actuator Installation
- When replacing a VGT actuator, the installation procedure should be followed carefully.
Air in Fuel Problem
- To verify an air in fuel problem, the fuel system should be inspected.
Hard Start in HEUI Fuel Injected Engine
- A hard start in a HEUI fuel injected engine is often caused by a faulty fuel pump or faulty injectors.
Cooling System
- If the temperature is not rising above 88°C (190°F) during operation of the cooling system, it may indicate a problem.
Restricted Exhaust System
- A restricted exhaust system can cause poor engine performance.
Engine Cooling Fan
- If the engine cooling fan is running continuously, the cooling system should be checked.
Pressure in DEF Lines
- If pressure is found in the DEF lines after the ignition is shut off, the DEF system should be checked.
Engine Compression Brake
- If the engine compression brake is weak and the engine warning light is illuminated, the brake system should be inspected.
Multiple Compression Brake Heads
- When removing multiple compression brake heads at once, a specialized tool may be required.
DEF Pump Operation
- The correct operation of a DEF pump can be confirmed by checking the pump's performance.
Piston Cooling Nozzle Replacement
- A broken piston cooling nozzle should be replaced according to the manufacturer's instructions.
Inlet Knox Sensor
- If the inlet Knox sensor is reading higher than normal, it may indicate a problem with the sensor or the intake system.
Oil Sample Collection
- The procedure for collecting an oil sample should be followed carefully to ensure accurate results.
Engine Regenerations
- If the engine is doing frequent regenerations and there is no check engine light visible, the diesel particulate filter may be clogged.
Broken Piston Cooling Nozzle
- A broken piston cooling nozzle can cause poor engine performance.
Oil Pan Replacement
- The procedure for replacing an oil pan on a truck should be followed carefully.
Engine Oil Consumption
- Excessive oil consumption in an engine may be caused by worn piston rings or cylinder walls.
Water Pump Replacement
- The procedure for replacing a water pump should be followed carefully.
Fuel Return Measurement
- A high rate of fuel return measured at the cylinder head return gallery in a high-pressure common rail system may indicate a problem with the fuel system.
Exhaust System Inspection
- The exhaust system should be inspected regularly to ensure it is functioning properly.
Replacing a Rex Sensor
- The procedure for replacing a rex sensor in a high-pressure common rail system should be followed carefully.
Cooling System Filter Replacement
- The cooling system filter should be replaced regularly to ensure the cooling system functions properly.
Turbocharger Failure
- After a major turbocharger failure, the engine should be inspected for damage.
Valve Clearance
- If valve clearance becomes tighter between adjustments, it may indicate a problem with the valve system.
Air Brake System
- The air brake system should be inspected regularly to ensure it is functioning properly.
Hydraulic Brake System
- The hydraulic brake system should be inspected regularly to ensure it is functioning properly.
S-Cam Bushing Clearance
- S-cam bushing clearance should be checked regularly to ensure it is within specifications.
Wheel Seal Replacement
- The procedure for replacing a wheel seal on an air brake system should be followed carefully.
Spring Chamber Removal
- The procedure for removing the spring chamber on an air brake system should be followed carefully.
Primary and Secondary Brake Systems
- The primary and secondary brake systems should be inspected regularly to ensure they are functioning properly.
Rotor Installation
- The procedure for installing a new rotor should be followed carefully.
Hydraulic Brake Caliper
- The hydraulic brake caliper should be compressed carefully to avoid damage.
Steering Axle Brake Line
- If a steering axle brake line is cracked, it should be replaced immediately.
System Air Pressure
- The system air pressure should be increased regularly to ensure the air brake system functions properly.
Chuff Test
- The chuff test should be performed regularly to ensure the air brake system is functioning properly.
Air Gauge Accuracy
- The accuracy of the air gauge pressure indicators should be verified regularly.
Trailer Brakes
- The trailer brakes should be inspected regularly to ensure they are functioning properly.
Brake Stroke
- A 76.2-mm (3in) brake stroke may indicate a problem with the brake system.
Air Leaks
- Air leaks in the treadle valve exhaust port should be repaired immediately.
Ride Height
- The ride height of a truck should be adjusted according to the manufacturer's specifications.
Service Air Brake
- The service air brake should be applied carefully to ensure it functions properly.
Bleeding Hydraulic Brake System
- The procedure for bleeding a hydraulic brake system should be followed carefully.
Battery Load Test
- A battery load test should be performed regularly to ensure the battery is functioning properly.
Multi-Coil Gasoline Engine
- A miss on cylinder 4 of a multi-coil gasoline engine should be diagnosed and repaired.
High Voltage System
- The high voltage system should be tested regularly to ensure it is functioning properly.
Battery Maintenance
- The battery should be cleaned and maintained regularly to ensure it functions properly.
Alternator Output Cable
- The alternator output cable should be replaced if it is damaged or worn.
Fuse Failure
- A blown fuse should be replaced with a new one of the same amperage rating.
LED Turn Signal Lights
- LED turn signal lights may blink rapidly if not installed correctly.
Swollen Wire
- A swollen wire may be caused by excessive heat or electrical surge.
SRS ECU Replacement
- The procedure for replacing an SRS ECU should be followed carefully.
Battery Discharge
- A slowly discharging battery may be caused by a faulty battery or electrical system.
Inverter Installation
- The procedure for installing an inverter should be followed carefully.
Coil on Plug Gasoline Engine
- During a tune-up on a coil on plug gasoline engine, certain components should be replaced.
Low Charging Condition
- A low charging condition may be caused by a faulty alternator or electrical system.
Starter Circuit
- The starter circuit should be tested regularly to ensure it is functioning properly.
Alternator Diagnosis
- An excessively hot alternator may indicate a problem with the electrical system.
Sensor Connector Replacement
- The procedure for replacing a sensor connector should be followed carefully.
Data Link Wires
- The procedure for replacing data link wires should be followed carefully.
Starter Motor
- The starter motor should be tested regularly to ensure it is functioning properly.
Master Lighting Switch
- The master lighting switch should be inspected regularly to ensure it is functioning properly.
Slow Engine Cranking
- A slow engine cranking condition may be caused by a weak battery or faulty starter motor.
Voltage Drop Measurement
- Voltage drop across the negative starter cable should be measured carefully.
3-Wire Sensor
- A 3-wire sensor should be tested regularly to ensure it is functioning properly.
Splice Joint
- A splice joint should be inspected regularly to ensure it is functioning properly.
Starter Solenoid
- A starter solenoid that remains engaged when voltage is removed should be replaced.
Axle Housing Leak
- An oil leak from the differential housing may be caused by a faulty seal or gasket.
Clutch Installation
- The procedure for installing a clutch assembly should be followed carefully.
Automated Transmission
- An automated transmission should be serviced regularly to ensure it functions properly.
Manual Transmission Oil
- Manual transmission oil should be checked regularly to ensure it is at the correct level.
Axle Removal
- The procedure for removing an axle from a differential should be followed carefully.
Speedometer Malfunction
- A malfunctioning speedometer may be caused by a faulty sensor or electrical system.
Shift Linkage Adjustment
- The shift linkage should be adjusted regularly to ensure it functions properly.
Electric Drivetrain Retarder
- An electric drivetrain retarder should be serviced regularly to ensure it functions properly.
U-Joint Grease
- A U-joint should be greased regularly to ensure it functions properly.
Wheel Rim
- A wheel rim that has turned on a spoke hub should be replaced immediately.
Front-End Alignment
- The front-end alignment should be checked and adjusted regularly to ensure proper vehicle alignment.
Spring Pack Repair
- A broken spring pack should be repaired or replaced immediately.
Hub Piloted Steer Wheel
- The procedure for installing a hub piloted steer wheel should be followed carefully.
Trailer King Pin Wear
- Trailer king pin wear should be inspected regularly to ensure it is within specifications.
Steel
This quiz covers the topic of identifying issues with axle wheel bearings, specifically focusing on the presence of blue discolouration. Test your knowledge on what the blue discolouration indicates and what actions are needed to address this problem.
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