Chery A15. Instruction - page 33

The ECU can indirectly control the purge airflow
through controlling the charging time of the carbon
canister solenoid valve based on the signals provided
by various sensors of the engine.

Fault diagnosis: The ECU doesn’t have the function of
self-diagnosis for the carbon canister control valve, but
has the function of self-diagnosis for the driving stage
of control valve of carbon canister. If the driving state
of the control valve of carbon canister is short or
overloaded to the battery voltage, short to ground or
open, the basic memory of the closed loop control of
fuel quantity will be closed, the memory of idling air
demand quantity will be closed and the memory data at
that time is valid. The common malfunctions of engine
are unstable idling or excessive high idle speed under
the malfunction of the solenoid valve of carbon
canister.

Pins:

1# pin is connected to the 87# pin on output terminal of
the main relay;
2# pin is connected to the 46# pin of ECU.

Troubleshooting: The blockage and crack of the
carbon canister will result in the increase of air intake.

Steel fuel distribution pipe assembly

Function: Store and distribute the fuel and provide a
relative stable pressure for the fuel injection system so
as to achieve the uniform fuel supply pressure and
quantity for each cylinder and stable operation of
engine.

Structure: The fuel distribution pipe assembly is
comprised of fuel distribution pipe (KVS-S) and fuel
injector (EV).

Installation requirement: The connection of fuel pipe
and rubber hose shall be fastened by clamp. The model
of the selected clamp shall match to the rubber hose to
ensure the seal connection between the fuel pipe and
the rubber hose.

Fault diagnosis: There is seldom possibility for the
malfunction occurrence in the main fuel supply pipe.
Most of the malfunctions, which result in the leakage of
the fuel system, are caused by poor assembly, so proper
note shall be paid during installation that any used
O-oil seal shall not be used again and appropriate
lubricant is allowed to be painted during assembly.

Carbon canister control valve

Carbon canister control valve

Circuit diagram of the solenoid valve
of the charcoal canister TEV-2

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BASIC PRINCIPLE OF FAULT DIAGNOSIS FOR ELECTRONIC

FUEL INJECTION SYSTEM

·RECORD OF MALFUNCTION INFORMATION

The electronic control unit consistently monitors the operations of sensors, actuators,
related circuits, malfunction alarm lights, voltage of battery and so on, even the
operation of the electronic control unit itself, as well as carries out the examination on
reliabilities of the signals output by the sensors, driving signals of actuators, and
internal signals (such as oxygen closed loop control, knock control, idle speed control,
battery voltage control and etc.). Once it is found that there is a malfunction in some
chain or some signal is not reliable, the electronic control unit will set the record of
malfunction information in the RAM of malfunction memory. The record of
malfunction information is stored as diagnostic trouble code and displayed in the
same order as the occurrence of the malfunctions.

Based on their frequency of occurrence, the malfunctions can be classified as “steady
state malfunction” and “random malfunction” (such as the malfunctions caused by
temporary circuit open of wiring harness or defective contact of connectors).

·MALFUNCTION STATUS

If the duration period of the identified malfunction exceeds its setting stabilizing time
at the first time, ECU will regard this malfunction as a stable malfunction and store it
in the memory of “steady state malfunctions”. If the malfunction disappears within its
setting stabilizing time, it will be stored as “random malfunction” or “non existence”.
If this malfunction is identified again, it will still be regarded as “random
malfunction”, but the “existence” of historic malfunction will not influence normal
operation of the engine.

·MALFUNCTION TYPES

Short to positive grid of power supply;

Short to ground;

Circuit open (if there is pull up resistance or pull down resistance in input stage, the
ECU will regard the malfunction of circuit open on input terminal as the malfunction
that the input terminal is short to power supply or to ground.);

Unreliable signals.

·FOUR TYPES OF MALFUNCTIONS

Maximum malfunction, the signal exceeds the upper limit of the rated range.

Minimum malfunction, the signal exceeds the lower limit of the rated range.

Signal malfunction, no signal.

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Illogical malfunction, there is signal but the signal is not logical.

·LIMP DRIVE

If some detected important malfunctions last longer than the setting stabilizing time,
ECU will take proper software measures, for example, disable some control functions
including the oxygen sensor closed loop control and the like, replace some unreliable
data with the setting values and etc.. Therefore even the working condition of the
engine is quite bad at that time, but the car still can be driven. The objective of such
measures is to drive home or drive to service station limpingly so as to avoid the
embarrassment that the car has to be broken down on highway or in field. As soon as
the detected malfunction disappears, the normal data will be reused.

·MALFUNCTION ALARM

Some cars equipped with M7.9.7 system have the malfunction alarm light. If some
important components such as ECU, the air intake manifold absolute pressure sensor,
the throttle position sensor, the coolant temperature sensor, the knock sensor, the
oxygen sensor, the phase angle sensor, the fuel injector, two drive stages of idle
actuator with step motor, the carbon canister control valve, the cooling fan relay have
malfunctions, when the corresponding malfunction flag bit is set, ECU will send
alarm through the malfunction alarm light until this malfunction flag bit is reset.

·MALFUNCTION READOUT

The malfunction information record can be called from the electronic control unit
through the diagnostic tester, or be read through the flashing code. If the malfunction
is related to the function of fuel air mixing ratio regulator, the corresponding
malfunction information record can be read at least 4 minutes after the engine starts
running.

ISO 9141-2 Standard diagnostic connector

Connection to the diagnostic tester

This system adopts the “K” line communication protocol, and utilizes the ISO 9141-2
standard diagnostic connector (shown in the above figure). This standard diagnostic
connector is fixed on the wiring harness of the engine. The 4#, 7#, and 16# pins of the
standard connector are connected to the engine management system (EMS), the 4#
pin is connected to the ground wire of the car, the 7# pin is connected to the 71# pin
of ECU (i.e. the “K” line of engine data), the 16# pin is connected to the positive grid
of the battery.

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The detailed procedures are:

Turn on the ignition switch, but not start up the engine, ground the 7# pin of ECU by
K wire for more than 2.5 seconds, then open the ground connection, after that the
coding light starts flashing.

After the K wire is grounded for more than 2.5 seconds the output of flashing code is
the value of P-CODE. For example, the flashing method of P0203 is: consecutive
flashes of 10 times-pause-consecutive flashes of 2 times-pause,-consecutive flashes of
10 times-pause-consecutive flashes of 3 times.

·CLEARING MALFUNCTION INFORMATION RECORD

After the malfunction is fixed, the malfunction information record in the memory
shall be cleared. Such malfunction information, which appeared at the time of ignition
but failed to be maintained to the end of stabilizing period, will not be recorded. If the
value Hz of frequency counter reaches 0, the malfunction information records in the
malfunction memory will be cleared automatically. The malfunction information
record will be cleared upon the demand of “clearing the malfunction memory”
through the diagnostic tester. The malfunction information records in the external
RAM can be cleared by disconnecting the connector of ECU or removing the wire of
the battery.

·TROUBLESHOOTING:

WE ONLY CAN KNOW THE ROUGH POSITion of the malfunction whose
malfunction information record is obtained through the above measures, and it doesn’t
mean that we have found out that malfunction exactly. Because any malfunction is
possibly caused by the damage of electric components (such as sensors, actuators or
ECU and the like), the circuit open, or the circuit short to ground or positive stud of
battery, even the mechanical malfunctions.

The malfunction is intrinsic and its appearance is various symptoms. After the
symptom is detected the diagnostic tester or the flashing code shall be used to search
the malfunction information record, and excluding corresponding malfunction based
on the malfunction information. And then carry out the troubleshooting based on the
symptom of the engine.





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