Chery A15 / 480 LHD model. Manual — part 84

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.

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.

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.

ISO 9141-2 Standard diagnostic connector

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.

DETAILED TABLE OF DIAGNOSTIC TROUBLE CODES

Diagnostic trouble code: P0107 “Undervoltage in circuit of air intake pressure
sensor”

Item

No.

Operation procedure

Inspection

results

Follow-up

procedure

1

Connect the diagnostic tester and adaptor,
and turn the ignition switch to “ON”
position.

Proceed to next

step.

Yes

Proceed to Step 5

2

Observe the “air intake pressure” in data
flow and verify that it is maintained at
101kPa (the exact value is determined by
the atmospheric pressure at that time).

No

Proceed to next

step.

Yes

Proceed to Step 5

3

Disconnect the connector of the air intake
pressure sensor on the wiring harness and
inspect with multimeter to verify that the
voltage between the 3# and 1# pins of the
connector is about 5V.

No

Proceed to next

step.

Yes

Repair or replace

the wiring

harness.

4

Verify that the circuits between the 17#,
33# and 37# pins of ECU and the 1#, 3#,
and 4# pins of the sensor connector are
short to ground.

No

Proceed to next

step.

Yes

Refer to diagnosis

help.

5

Start up the engine, run at idle speed. Step
on the accelerator pedal slowly until the
nearly full opening, observe the “air intake
pressure” displayed on the diagnostic
tester and verify that the value is stable
without significant change; if step on the
accelerator pedal quickly until nearly full
opening, whether the value exceeds 90kPa
instantaneously.

No

Replace the

sensor.

Yes

Refer to diagnosis

help.

6

Start up the engine, run at idle speed.
Observe

the

value

of

“Coolant

temperature” on the diagnostic tester to
verify that the indicated value is increased
along with the temperature increase of the
engine coolant.

No

Replace the

sensor.