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Vehicle Fault Finding
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    • by Peugeot Pete



VEHICLE FAULT FINDING - USEFUL TIPS FOR CAR FAULT FINDING

INTRODUCTION

The vehicle owner who does his or her own maintenance according to the recommended service schedules should not have to visit and use this section. Modern component reliability is such that, provided those items subject to wear or deterioration are inspected or renewed at the specified intervals, sudden failure is comparatively rare. Faults do not usually just happen as a result of sudden failure, but develop over a period of time. Major mechanical failures in particular are usually preceded by characteristic symptoms over hundreds or even thousands of miles. Those components which do occasionally fail without warning are often small and easily carried in the vehicle.

With any fault-finding, the first step is to decide where to begin investigations. Sometimes this is obvious, but on other occasions, a little detective work will be necessary. The owner who makes half a dozen haphazard adjustments or replacements may be successful in curing a fault (or its symptoms), but will be none the wiser if the fault recurs, and ultimately may have spent more time and money than was necessary. A calm and logical approach will be found to be more satisfactory in the long run. Always take into account any warning signs or abnormalities that may have been noticed in the period preceding the fault - power loss, high or low gauge readings, unusual smells, etc - and remember that failure of components such as fuses or spark plugs may only be pointers to some underlying fault.

The pages which follow provide an easy-reference guide to the more common problems which may occur during the operation of the vehicle. These problems and their possible causes are grouped under headings denoting various components or systems, such as Engine, Cooling system, etc. Whatever the fault, certain basic principles apply. These are as follows:

Verify the fault. This is simply a matter of being sure that you know what the symptoms are before starting work. This is particularly important if you are investigating a fault for someone else, who may not have described it very accurately.

Don’t overlook the obvious. For example, if the vehicle won’t start, is there fuel in the tank? (Don’t take anyone else’s word on this particular point, and don’t trust the fuel gauge either!) If an electrical fault is indicated, look for loose or broken wires before digging out the test gear.

Cure the disease, not the symptom. Substituting a flat battery with a fully-charged one will get you off the hard shoulder, but if the underlying cause is not attended to, the new battery will go the same way. Similarly, changing oil-fouled spark plugs for a new set will get you moving again, but remember that the reason for the fouling (if it wasn’t simply an incorrect grade of plug) will have to be established and corrected.

Don’t take anything for granted. Particularly, don’t forget that a “new” component may itself be defective (especially if it’s been rattling around in the boot for months), and don’t leave components out of a fault diagnosis sequence just because they are new or recently-fitted. When you do finally diagnose a difficult fault, you’ll probably realize that all the evidence was there from the start.

Engine
Engine fails to rotate when attempting to start
Engine rotates, but will not start
Engine difficult to start when cold
Engine difficult to start when hot
Starter motor noisy or excessively-rough
    in engagement
Engine starts, but stops immediately
Engine idles erratically
Engine misfires at idle speed
Engine misfires throughout
    the driving speed range
Engine hesitates on acceleration
Engine stalls
Engine lacks power
Engine backfires
Oil pressure warning light illuminated
    with engine running
Engine runs-on after switching off
Engine noises

Cooling system
Overheating
Overcooling
External coolant leakage
Internal coolant leakage
Corrosion

Fuel and exhaust systems
Excessive fuel consumption
Fuel leakage and/or fuel odor
Excessive noise or fumes from exhaust system

Clutch
Pedal travels to floor
    - no pressure or very little resistance
Clutch fails to disengage (unable to select gears)
Clutch slips (engine speed increases,
    with no increase in vehicle speed)
Judder as clutch is engaged
Noise when depressing or
    releasing clutch pedal

Manual transmission
Noisy in neutral with engine running
Noisy in one particular gear
Difficulty engaging gears
Jumps out of gear
Vibration
Lubricant leaks
Automatic transmission
Fluid leakage
Transmission fluid brown, or has burned smell
General gear selection problems
Transmission will not downshift (kick down)
    with accelerator fully depressed
Engine will not start in any gear,
    or starts in gears other than Park or Neutral
Transmission slips, shifts roughly, is noisy,
    or has no drive in forward or reverse gears

Driveshaft
Clicking or knocking noise on turns
    (at slow speed on full-lock)
Vibration when accelerating or decelerating

Braking system
Vehicle pulls to one side under braking
Noise (grinding or high-pitched squeal)
    when brakes applied
Excessive brake pedal travel
Brake pedal feels spongy when depressed
Excessive brake pedal effort required to stop vehicle
Judder felt through brake pedal or
    steering wheel when braking
Brakes binding
Rear wheels locking under normal braking

Suspension and steering systems
Vehicle pulls to one side
Wheel wobble and vibration
Excessive pitching and/or rolling around
    corners, or during braking
Wandering or general instability
Excessively-stiff steering
Excessive play in steering
Lack of power assistance
Tire wear excessive

Electrical system
Battery will not hold a charge for more than a few days
Ignition/no-charge warning light remains
    illuminated with engine running
Ignition/no-charge warning light fails to come on
Lights inoperative
Instrument readings inaccurate or erratic
Horn inoperative, or unsatisfactory in operation
Windscreen/tailgate wipers inoperative,
    or unsatisfactory in operation
Windscreen/tailgate washers inoperative,
    or unsatisfactory in operation
Electric windows inoperative,
    or unsatisfactory in operation
Central locking system inoperative,
    or unsatisfactory in operation
 


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