Dashboard warning lamp
We DO NOT recommend vehicle operation
is continued with a warning lamp or
warning message active – It is a
warning for a reason !
First check your owners manual to find out what the warning light refers to.
Operation sequence of most engine
system related dashboard warning lamps illuminate when the key is
switched to ignition position and should go out when the vehicle engine is running.
Engine warning lamp:
Illumination of the check engine or engine management warning
( MIL ) lamp indicates that the
vehicle engine management computer (ECU , ECM ,PCM)
has identified a fault related to the efficient running of the
engine and probably affecting exhaust
Vehicles with diesel
engines may also use the glow plug pre
heat warning lamp to indicate engine
check engine warning light comes on
engine operation a fault code
has almost certainly been logged by
the engine control system, and
consequently the engine control strategy may revert to limp home or restricted
Logged engine management faults in some cases may
prevent the engine from
running by software function..
Limp home mode will usually be noticed by the driver because of poor acceleration, shuddering, restricted performance, or the engine will not rev above a certain rpm.
What causes the engine
management lamp to light up ?
Sensor Inputs : The value expected from each
engine sensor is programmed into the
software of the engine control module and represented as a map
or lookup table. (Fuel map, Ignition
An out of range value may represent a faulty component
, wiring circuit or mechanical
The check engine lamp
may illuminate to notify the driver
that a fault has been detected for
example when a value exceeds parameters programmed in to engine controller memory map.
Retrieval of fault codes
Most modern vehicles require diagnostic equipment with
software to interrogate the ecm for
stored fault codes.
Automotive system electrical diagnostics
interrogation scan of the vehicle computer for stored fault
codes using suitable diagnostic equipment such as a scan tool fault code reader.
Some older vehicles (usually
Japanese) have a self diagnosis function allowing the the fault code to be read by counting the flashes of the check
engine light and looking up the value in a reference table.
Historical fault codes
Intermittent faults which occur during driving
may be logged as an error fault code
which causes the dashboard warning
light to illuminate..
Random disconnecting of electrical connectors in
the engine bay may also cause
fault codes to be logged.
EOBD fault codes
The term EOBD refers to European On
Board Diagnostics. EOBD
standards apply to Petrol vehicles
from May 2001 on , and Diesel vehicles
from 2003 on.
EOBD Fault codes , sometimes referred
to as P.... codes
are generally logged for factors which
affect vehicle exhaust emissions.
monitoring has various modes including
Freeze frame Data, which can be useful
to help diagnostics.
Vehicle Manufacturer specific fault codes
Vehicle manufacturers use their
own specific fault codes relating to
in depth component functions not
covered by EOBD
Engine Management Memory Reset
equipment will reset the control
system computer software and turn the warning
light off , however if a fault is
still present the check light will
often illuminate again once a
driving cycle has been completed until
the fault has been rectified. In some
cases several error codes may be
Electronic engine Management
Exhaust Gas Recirculation (EGR)
computer module compares values from various
sensors to calculate;
sensor, brake pedal switch,clutch switch,etc
Position of mechanical components
Using Crankshaft position sensor ,
Cam position sensor
How hot or cold the engine is (intake air temperature,coolant temperaure)
Engine speed and load
airflow sensor, manifold absolute pressure
(vacuum) , turbocharger boost pressure
Lambda or Oxygen sensor operation
Test and Repair
Following testing, a faulty wiring circuit may be repaired or component
adjusted , cleaned or replaced.
Diagnostic Equipment Functions
Our diagnostic equipment is capable of Fault code reading Actuator testing
to verify wiring circuits
by operating the suspect component on a wide range of vehicle systems. The actuator test function can allow some components
to be thoroughly cleaned which may save replacement cost.
Programming and Coding
components such as electronic fuel
injectors , throttle bodies etc may need coding to the
Advanced system testing can be
carried out using oscilloscope
signal test methodsReset Procedures
Following repair work the fault code memory of the vehicle computer will need to be reset to clear stored fault codes.
Engine Sensors, Actuators , and Common Faults
Exhaust gas recirculation ( EGR )
system functions to reduce combustion
temperature and oxides of Nitrogen
( Note : not Nitrous oxide !) EGR and Idle speed control ( ISC ) devices are particularly prone to failure due
to build up of carbon and soot deposits
which can restrict the air inlet
system of the engine.
EGR systems may cause
the MIL warning lamp to illuminate
intermittently and flag a P0400 EOBD
fault code due to "critical system
malfunction" as described on certain
diagnostic equipment !
Mechanical position sensors
Cam position sensor :
used to identify cylinder phasing
Crankshaft (CKP)position sensor
: Identification of engine
crankshaft position and calculation
of engine speed and combustion
forces. Frequency and amplitude
signal is proportional to engine
Symptoms: Non Start, Misfire
Typical failure : Signal
errors can occur due to sensor
failure , phonic wheel damage,
wiring connection failure, loss of
synchronisation between crankshaft
Throttle position sensor (TPS)
/ Accelerator Position sensor (APP)
function:Driver demand signal. TPS failure may occur due to
wear of potentiometer track causing
flat spots and hesitation when
Brake Pedal Position & Clutch
Pedal Position sensors used to
reduce to stabilise idle speed and
fuel delivery quantity when
engine is off load . Faults may
occur due to worn out switches
resulting in false (implausible)
Mass Air Flow (MAF) sensor
measures volume of air entering air
intake , Air Mass Meter measures
weight of air entering intake
tract. Engine load sensor which can
effect fuel metering (petrol
engine) or EGR position (diesel
Intake Air Temperature Sensor
may be incorporated with air mass
meter , with MAP sensor (T-MAP) or
Manifold Absolute Pressure
(MAP) sensor measures engine load
by vacuum (petrol engines) or boost
pressure (turbocharged engines) at intake manifold. Split
or blocked pipes can effect
operation. MAP signal can influence
fuel control, EGR, and turbo boost.
Temperature measurements may be
signalled by either coolant
temperature sensor or cylinder head
temperature sensor. Temperature
signal is processed to compensate
engine smooth running by control of
fuel delivery egr position, &
diesel pre heat function.
Fuel Delivery System :
Low and high pressure fuel
injection pumps, pressure
regulator, fuel injectors. Prone to
faults caused by fuel contamination
, and general wear.
Boost pressure control :
turbocharger waste gate position
and hence boost pressure control is
often actuated by solenoids
controlling vacuum circuits. Common
faults can include loss of vacuum
due to vacuum pump wear, split or
blocked vacuum pipes, electrical
circuit faults with control,
solenoid or wiring.
Lambda Sensor (as fitted
to Petrol & Gas
oxygen content of exhaust gas and
is used as a feedback signal to
control fuel quantity delivery. Can
deteriorate due to age and
contamination. Lambda sensor fault
codes may also relate to problems
other than the sensor itself.
Lambda sensor operation can is
affected by sensor temperature .Lambda sensor feedback signal is
only used when engine operating
temperature is sufficient to enable
closed loop control status.
lambda sensor may be fitted in the
exhaust system after the catalytic
convertor to monitor condition of
supply a range of replacement
sensors and actuators at
Anti-theft Immobiliser warning lamp
This may flash as the engine is cranked whilst the immobiliser is active.
Manufacturer or OEM immobiliser systems are often integrated into a vehicle on board computer system and may prevent starting, ignition, or
fuelling circuits from operating.
Faults can sometimes occur if a
receiver does not recognise the signal
transmitted by a coded key or remote,
or no transmission due to defective
remote/discharged battery, or broken
wiring causing CAN signal faults.
This type of system can rarely be bypassed other than by reprogramming.
Aftermarket alarm and immobiliser systems are installed as an added security measure by some owners. If these systems
fail they can normally be removed or bypassed by an autoelectrician to enable vehicle operation.
You should check with your
insurance company if an aftermarket alarm is to be removed as this may affect insurance policy validation.
There is more information about alarms & immobilisers on our vehicle security page.