Fault Finding REF•11
The vehicle owner who does his or her own maintenance according
to the recommended service schedules should not have to use this
section of the manual very often. 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. The Chapter and/or Section which deals with the
problem is also shown in brackets. 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 petrol 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 realise
that all the evidence was there from the start.
Engine
Engine fails to rotate when attempting to start
mm Battery terminal connections loose or corroded (Chapter 5).
mm Battery discharged or faulty (Chapter 5).
mm Broken, loose or disconnected wiring in the starting circuit (Chap-
ter 5).
mm Defective starter solenoid or switch (Chapter 5).
mm Defective starter motor (Chapter 5).
mm Starter pinion or flywheel ring gear teeth loose or broken (Chap-
ter 5).
mm Engine earth strap broken or disconnected (Chapter 5).
mm Automatic transmission not in Park/Neutral position, or selector
lever position sensor faulty (Chapter 7, Part B).
Engine rotates but will not start
mm Fuel tank empty.
mm Battery discharged (engine rotates slowly) (Chapter 5).
mm Battery terminal connections loose or corroded (Chapter 5).
mm Ignition components damp or damaged (Chapters 1 and 5).
mm Broken, loose or disconnected wiring in the ignition circuit
(Chapters 1 and 5).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Low cylinder compressions (Chapter 2, Part A, B or C).
mm Major mechanical failure (eg camshaft drive) (Chapter 2,
Part A, B or C).
Engine difficult to start when cold
mm Battery discharged (Chapter 5).
mm Battery terminal connections loose or corroded (Chapter 5).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Other ignition system fault (Chapters 1 and 5).
mm Engine management system fault (Chapters 1 and 4).
mm Low cylinder compressions (Chapter 2, Part A, B or C).
Engine difficult to start when hot
mm Air filter element dirty or clogged (Chapter 1).
mm Engine management system fault (Chapters 1 and 4).
mm Low cylinder compressions (Chapter 2, Part A, B or C).
mm Faulty hydraulic tappet(s) (Chapter 2, Part A, B or C).
Starter motor noisy or excessively-rough in
engagement
mm Starter pinion or flywheel ring gear teeth loose or broken (Chap-
ter 5).
mm Starter motor mounting bolts loose or missing (Chapter 5).
mm Starter motor internal components worn or damaged (Chapter 5).
Engine starts but stops immediately
mm Loose or faulty electrical connections in the ignition circuit
(Chapters 1 and 5).
mm Engine management system fault (Chapters 1 and 4).
mm Vacuum leak at the inlet manifold (Chapters 1, 2 and 4).
Engine idles erratically
mm Engine management system fault (Chapters 1 and 4).
mm Air filter element clogged (Chapter 1).
mm Vacuum leak at the inlet manifold or associated hoses (Chap-
ters 1, 2 and 4).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Faulty hydraulic tappet(s) (Chapter 2, Part A, B or C).
mm Uneven or low cylinder compressions (Chapter 2, Part A, B or C).
mm Camshaft lobes worn (Chapter 2, Part A, B or C).
mm Timing belt incorrectly-tensioned (Chapter 2, Part A or B).
Introduction
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