Chery QQ6 (S21) / S12LHD. Manual — part 104

Clutch position switch provides ECU with the signal of clutch position, but this signal can only

be used to distinguish between disengaging and engaging positions of the clutch.

17.2 Working principle:

ECU provides clutch position switch with a 12V power supply; when the clutch is under

disengaging state, the power supply will ground and ECU will lose 12V high potential signal, by

which the position of the clutch can be judged.

18. A/C Control

By receiving the A/C signal from A/C switch, ECU can control working of A/C compressor.

ECU also can receive the signals from high and low pressure switches of A/C to ensure safety of A/C

system. When A/C signal is sent to ECU through high and low pressure switches, if the low pressure

switch breaks, ECU will not receive the A/C signal; the compressor is thus unable to work. If A/C

system has a too high pressure, the high pressure switch will break and A/C signal can not be

provided to ECU; so, ECU will immediately cut off the compressor. When system pressure is normal

or a little higher (medium pressure), the medium pressure switch will cut in; thus, ECU can control

the fan to run immediately at high speed to ensure a system pressure within the normal range.

Cut off pressure of the low pressure switch: 0.12Mpa

Cut-in pressure of the medium voltage switch: 1.6Mpa

Cut off pressure of the high pressure switch: 3.2Mpa

Through evaporator temperature sensor of the A/C system, ECU

can also protect the A/C system and prevent evaporator case from

freezing. When the temperature provided by the evaporator

temperature sensor is blow 3.75

, ECU will cut off the

℃

compressor; when the temperature is above this degree, ECU will

automatically engage the compressor to let it work.

离
合
器
位
置
开
关

C

lu

tc

h

po
siti

on
s

w

it

ch

开关

高
低
压
开
关

中
压
开
关

M

ediu

m

v

o

lt

ag

e

sw

it

ch

H

igh

a

n

d

l

o

w

v

o

lt

a

g

e

sw

it

ch

A/C switch

Chapter Two Fundamental Principle for Failure Diagnosis of

Electronic Fuel Injection System

1. Failure Information Records

The ECU monitors sensor, actuator, related circuit, malfunction indicator and

battery voltage etc., and even EUC itself continuously. At the same time, the ECU
inspect the reliability test on sensor signal output, actuator driving signal and internal
signal (e.g.: closed loop control, knock control, idle speed control and accumulator
voltage control etc.). ECU will set the malfunction record on RAM malfunction
memory immediately once the malfunction or the unlikelihood signal is detected. The
failure information records are stored in the form of diagnostic trouble code (DTC) and
are displayed in the precedence order of occurrence of the failures.

Failures can be divided into “stable state failures” and “random failures” (for example,
caused by transient open circuit of wires or poor contact of inserted parts) by failure
frequency.

2. Failure State

Once duration of occurrence of an identified failure exceeds the given stabilization time
for the first time, ECU will account it as a stable failure and then store it as a “stable
state failure”. If this failure disappears, it will be stored as a “random failure” and
“non-existent”. If this failure is identified again, it will still be a “random failure”, but a
“existent” early failure that will not affect average service of the engine.

3. Failure Types

Short circuit to positive pole of power supply
Short circuit to ground
Open circuit (for the case where there are pull-up resistors or pull-down resistors during
input stage, ECU will recognize failure of open circuit at input port as that of short
circuit to positive pole of power supply or that of short circuit to ground)
Signals can not be used

4. Failure Frequency Counter

For every identified failure, a separate frequency counter numerical value (Hz) will be
set.
This numerical value (Hz) for frequency counter determines the time this failure

information record will be stored in memory after the identified failure disappears (after
troubleshooting).
When a failure is identified for the first time, Hz will be set as its initial value 40. If
failure status does not change, then this numerical value will maintain all along.
Once it is identified that this failure has disappeared and the state has held for a certain
time, whenever the engine starts with success (its engine speed has exceeded the value
at end of starting) once, Hz will decrease by 1. At this point, ECU will believe that this
failure has disappeared, but the failure information record still exists.
If a failure (for example, as a result of poor contact) frequently appears and disappears,
then Hz will increase by 1, but will not exceed its given upper limit value 100.
If value of Hz has been decreased to zero, the failure information records in this failure
memory will be completely cleared.

5. Limp Home

For some identified significant failures, when duration exceeds the given

stabilization time, ECU will take appropriate software countermeasures, for example,
closing some control functions such as closed loop control of oxygen sensor etc. and
setting substituted values for some data that are considered to be suspect and so forth.
At this point, though the working condition of the engine is comparatively poor, the
auto can still run. The purpose to do this is to enable the auto limply run home or to a
service station for overhaul, so as to avoid the embarrassment that the auto breaks down
on highway or afield. Once it is identified that the failure has disappeared and Hz has
fell to below 40, use of normal data will be resumed again.

6. Failure Alert

In the electric control system, when failure take places in any of such important

parts as ECU, absolute pressure sensor in intake manifold, throttle position sensor,
coolant temperature sensor, knock sensor, oxygen sensor, phase sensor, injector, two
driver stages of step motor of idle speed actuator, canister control valve, or fan relay at
corresponding failure location, ECU will give an alarm through lightening of failure
indicator lamp until this failure location restores.

7. Readout of Failure

The failure information records can be called out of ECU through a trouble diagnosis
tester. If the failure relates to the function of mixed air (fuel and air) proportional
regulator, then the engine must at least run for 4 minutes before reading out failure
information records; especially for failure in oxygen sensor, be sure not to detect data
until the engine runs and warms up.
- -



Figure 3-1 ISO 9141-2 Standard Diagnostic Connector

8. Clearing Failure Information Records

After the failure is removed, the failure information records in memory should be

cleared. The diagnostic trouble code can be cleared through the following approaches:
When the numerical value of frequency counter in ECU reaches zero, the failure
information records in failure memory will be automatically cleared.
Employing fault diagnostic tester to clear records of failure with the instruction of “reset
memory for records of failure”.
Pulling out connectors of ECU or disconnecting wires of battery to clear records of
failure in external ram.

9. Failure Locating

After obtaining failure information records through above means, only rough

location where the failure takes place is aware, but this does not mean that the failure
has been located; because the cause that triggers a piece of failure information may be
damage of electric element (such as sensor, actuator or ECU etc.), lead break, lead
short-circuit to ground or anode of battery, even may be mechanical failure.

The failure is intrinsic and the result of its extrinsic representations is a variety of

symptoms. After a symptom is found, first, check for failure information records with a
trouble diagnosis tester or based on the flash code, after that, remove the correlated
failure in accordance with the failure information, and then locate the failure based on
symptom of the engine.

10. Failure Code Table

No.

DTC

Explanation

Failure

class

1

P0016

Improper relative installation position between camshaft and crankshaft

class5

2

P0030

Failure in heating control circuit of upstream oxygen sensor

class31

3

P0031

Too low voltage in heating control circuit of upstream oxygen sensor

class31