Chery A series. Manual - part 33

 

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. 

 

G-21

 

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. 

 

G-22

 

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. 

 

 
 
 
 
 
 
 
 
 

 

G-23

 

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. 

 

G-24