1987 SUZUKI GRAND VITARA check engine

Checking feed back system circuits
When the feed back system does not seem to operate properly even after each of its components has been
checked and proved normal, it is necessary to check each circuit of the feed back system. The checking
procedure of each circuit is described here.
[Checking ECM ground circuits]
The ECM is grounded both at the dash panel and
the intake manifold. If either grounding is not
made securely, the feed back system will not
operate. Therefore, check if the ECM is properly
grounded at these two points according to the
following procedure.
1) Turn OFF the ignition switch.
2) Disconnect the coupler from the ECM.
3) Connect an ohmmeter between the terminal
@ of the disconnected coupler (on the
wiring harness side) and the body (ground)
as shown in below figure, and measure the
resistance. Then repeat the same with the
terminal 0.1. ECM (Electronic Control2. CouplerModule)3. Instrument main panel
Fig. 5-3-38 ECM and coupler
1. Coupler (Viewed from wire harness side)
2. “B” (Black) leed wire
3. “B/G” (Black/Green) lead wire
4. Body ground
5. Engine ground
Fig. 5-3-39Checking ECM ground circuit
5-29

4) If the measured resistance between each terminal ( @ and @ 1 and the body is “ZERO (0)” ohm, the
ECM is grounded securely at two points. If the resistance is not “ZERO (0)” ohm, the possibility is
that the lead wire between the terminal (0 or @ ) and the ground is not securely grounded or
disconnected.
The below figures show the particular points where “B” and “B/G” wires are grounded. Check for
their secure grounding by referring to these figures.
1. Body ground3. Dash panel2. Black/Green lead wire 4. Battery
Fig. 5-3-40 Body ground
1. Engine ground3.Thermostatcap
2. Black lead wire4.Intake manifold
Fig.5-3-41Engine ground
5) After checking, connect the coupler to ECM securely.
5-30

[Checking ECM power circuits]
Connected to the ECM are the ignition coil and solenoids or solenoid valves. If a disconnection or a
failure of contact occurs within a circuit (power circuit) including any of these coil or solenoids or sole-
noid valves, signals will not be sent to the ECM and as a result, the feed back system will not operate
properly. Therefore, check the power circuits according to the following procedure.
1) Disconnect the coupler connected to the ECM.
2) Turn ON the ignition switch but be sure not to run the engine.
3) Connect a voltmeter between the terminal @ of the disconnected coupler (on the wiring harness side)
and the body (ground) as shown in below figure and measure the voltage. And then repeat the same
with each of the terminals 0, 0, 0, 0, 8, @ and 0. If the measured voltage between each
terminal and the body is about 12V, each circuit is in good condition.
4) If about 12V is not obtained in the above check, the particular circuit may be disconnected or out of
contact. Check the circuit for such conditions.
5) After checking, connect the coupler to ECM securely..
1. Coupler (Viewed from wire harness side)10. Three way solenoid valve (EGR system)
2. Battery11. Br (Brown) lead wire
3. Ignition switch (ON)!2. BI/R (Blue/Red) lead wire
4. Ignition coil13. B/W (Black/White) lead wire
5. Vacuum switching valve14. Br/W (Brown/White) lead wire(secondary throttle valve)15. BI/B (Blue/Black) lead wire6. Three way solenoid valve (Idle-up)16. BI/Y (Blue/Yellow) lead wire7. Mixture control solenoid17. BI/W (Blue/White) lead wire8. Switch vent solenoid18. BllG (Blue/Green) lead wire9. Fuel cut solenoid valve
Fig. 5-3-42 Checking ECM power circuits

[Checking sensors and their lead wires]
The sensors constituting the feed back system are; wide open micro switch, idle micro switch, thermal
switch, high altitude compensator, thermal engine room switch and fifth switch. If any of the above
sensors malfunctions or if the sensor circuit has some trouble, signals are not sent to the ECM and conse-
quently the feed back system will not function properly.
Therefore, check each sensor and its circuit according to the following procedure.
1) Turn OFF the ignition switch.
2) Disconnect the coupler from the ECM.
3) Connect the ohmmeter between the terminal @ of the disconnected coupler and the terminal @
(ground) as shown in below figure and measure the resistance. And then repeat the same with each of
the terminals 0, @I, @I, @ and @I.
1. Coupler (Viewed from wireharness side)
2. Wide open micro switch3. idle micro switch
4. Thermal switch
5. Thermal engine room switch6. Fifth switch
7. High altitude compensator
8. Gr/R (Gray/Red) lead wire9. Gr/Y (Gray/Yellow) lead wire10. 81 (Blue) lead wire
11. P/B (Pink/Black) lead wire
12. Gr/B (Gray/Black) lead wire
13. Lg/R (Light green/Red) lead wire
14. B/G (Black/Green) lead wire
Fig. 5-3-43 Checking sensors and their circuits
4) If each ohmmeter reading is as given below, the sensor and its circuit are in good condition. But if not,
the sensor itself may be defective or the lead wire disconnected or out of contact. After checking,
connect the coupler to ECM securely.
Idle micro switch
High altitude compensator
Thermal engine room switch
Wide open micro switch
1 Fifth switch

Ohmmeter
Terminal reading (S2)Condition
When coolant temp. is low.
When coolant temp. is above 46.5’C (I 16’F).
0 1
When engine is warm and accelerator pedal is not depressed.
When accelerator pedal is depressed a little.
00
@
When altitude is below 1,220 m (4,000 ft.).
0When altitude is above 1,220 m (4,000 ft.).
0
When temp. in engine room is low.
When temp. in engine room is above 19.5’C (67°F).
0When accelerator pedal is not depressed or depressed only a
0little.
CoWhen accelerator pedal is depressed all the way.
@ Oa
When gear shift lever is shifted to low, second, third, forth or
reverse gear position.
0When gear shift lever is shifted to fifth gear position.
5-32

[Checking function of oxygen sensor and feed back system1
If oxygen sensor fails to send signal to the ECM, the feed back system does not operate. While the feed
back system is at work, the ECM sends out the feed back signal, and in this condition, after warming up
engine to normal operating temperature, when the cancel switch or check switch, is turned ON, the “CHECK
ENGINE” light in the instrument cluster flashes. If the “CHECK ENGINE” light does not flash in such
conditions as described above, check the feed back system for function according to the following pro-
cedure.
NOTE:
Except for Canadian specification vehicle, also when mileage sensor is turned ON (the odometer indicates
50,000, 80,000 or 100,000 miles), the “CHECK ENGINE” light flashes. If the “CHECK ENGINE” light
does not flash in such condition, check the feed back system for function according to the following
procedure.
1) Remove the ECM from the instrument main panel.
2) Connect the coupler to the ECM..
(Don’t disconnect the coupler from the ECM if connected)
3) Warm up the engine to the normal operating temperature and keep it at idle.
4) Connect voltmeter between the terminals @I (oxygen sensor signal) and @ (ground) as shown in below
figure.
5) If the voltmeter indicator deflects between OV and 0.8V while racing the engine at a speed between
idling and 1,500 - 2,000 rpm, the feed back system is in good condition.
Fig,
NOTE:
Never connect ohmmeter as it may
cause damage to the oxygen sensor.
U.S.A. specification vehicle
1.ECM2. Coupler (Connected to ECM)
3.Oxygen sensor
4.Sealed wire5. W (White) lead wire
6. I3 (Black) lead wire7. Br/B (Brown/Black) lead wire8.Cancel switch9.“CHECK ENGINE” light
10. Ignition switch (ON)11.Battery
12.Mileage sensor115 'L----JA Canadian specification vehicle
I 5-3-44 Checking oxygen sensor signal
13. Check switch
6) If the indicator does not deflect between OV and 0.8V, possible causes are as follows.
Voltmeter indicator:
Remains at “Zero (0)“V
Possible causes
0 Oxygen sensor lead wire is disconnected or out of contact.
0intake system is leaky or air/fuel mixture is too lean due to malfunction
of carburetor,
0Inner resistance of voltmeter is too small.
0 Oxygen sensor is defective.
Indicates about 0.8V and does not
deflect.
0Choke is operating because engine is not warmed up fully.
0 Thermal switch is defective.
0 Wide open micro switch is defective.
0Lead wire of mixture control solenoid is disconnected.
0 Mixture control solenoid valve is defective.
5-33

7) After it isconfirmed through steps 1) to 5) that oxygen sensor sends signals to ECM properly, check feed
back signal according to the following procedure. If feed back system operates properly, ECM should
send out feed back signal.
a) Connect an ohmmeter between terminal @I and body (ground). Be sure to connect positive (+) prod
of the ohmmeter to body (ground) and negative (-) prod to terminal @J as shown in below figure
and never connect the other way around.
NOTE:
For this check, cancel switch must be OFF (“CHECK ENGINE” light off).
b) If indicator of ohmmeter deflects when connected as described in the above step, it means that ECM
sends out feed back signal, that is, feed back system operates properly.
NOTE:
If indicator doesn’t deflect at all, reverse connection (positive prod to terminal @ and negative prod to
body) and check.
In this state, turning ON cancel or check switch causes “CHECK ENGINE” light to flash. If “CHECK
ENGINE” light does not flash, wire harness, bulb of light or cancel/check switch may be defective.
8) After checking, install ECM to instrument main panel, and make sure coupler is connected to ECM
securely.
”1,
009
7
kr
1. ECM
2. Coupler (Connected to ECM)3. Oxygen sensor4. Sealed wire
5. Br/B (Brown/Black) lead wire6. Cancel switch (OFF position)
7. “CHECK ENGINE” light
8. Ignition switch9. Battery
/
ICanadian specification vehicle
U.S.A. specificationvehicle
10. Mileage sensor
11. Check switch
Fig. 5-3-45 Checking feed back signal
5-34

[Checking idle-up signal]
The idle-up system operates when any of the small lights (such as tail light, side marker light and license
light), heater fan and rear defogger is put in operation. If the idle-up actuator fails to operate even when
any of such equipments is put in operation, check if signal is sent to the ECM according to the following
procedure.
1) Disconnect the coupler from the ECM.
2) Turn ON the ignition switch but don’t run the engine.
3) Connect a voltmeter between the @ terminal and the body (ground) as shown in below figure. If the
voltmeter indicates 11 - 14V when each equipment is operated individually, it means that idle-up
signal is sent to the ECM.
If the voltmeter does not indicate 11- 14V, the particular circuit is disconnected or in poor contact.
Check the circuit for such conditions.
4) After checking, connect the coupler to ECM securely.
1.Coupler
2. 3.Small Heater lights fan
4. Rear defogger (if equipped)5. Ignition switch (ON)6. Battery
7. Br/Y (Brown/Yellow)
4
&
lead wire
Fig. 5-3-46 Checking idle-up signal
5-35

[Replacing ECMIFUEL CUT SYSTEM
If a malcondition such as those listed below still
occurs even after confirming proper function
and condition of the sensors of the feed back
system and their circuits through the above
checks, a trouble may exist within the ECM. In
such a cause, replace the ECM.
l Fuel consumption increases even in normal
Checking fuel cut system
1) Make sure that fuel cut solenoid valve makes a
clicking sound when ignition switch is turned
to “ON” or “OFF” without cranking engine.
driving.
l Engine tends to stall.
l Engine is hard to start.
SWITCH VENT SOLENOID
Checking switch vent solenoid
1) Disconnect canister hose from switch vent
solenoid and connect a new hose to the pipe
of solenoid.
2) Blow air into new hose with ignition switch at
both “OFF” and “ON” (but without starting
engine) and check to be sure that air passes
through solenoid in both cases.
1. Carburetor
2. Fuel cut solenoid valve
Fig. 5-3-48 Fuel cut solenoid valve
2) Warm up engine to normal operating tempe-
rature.
3) Increase engine revolution to 3,000 - 3,500
rpm. Under these conditions, check to be sure
that engine rpm changes when idle micro
switch lever on carburetor is moved as shown
in below figure.
1. Switch vent solenoid2. Canister hose (new)3. Blow air
Fig. 5-3-47 Checking switch vent solenoid
Do not suck the hose. The fuel vapor m
3) Start engine and run it at idle speed. Then
check to be sure that air does not pass through
solenoid when blowing air into new hose.
4) Remove new hose and connect original hose
to switch vent solenoid.
1. Carburetor
2. Idle micro switch lever
Fig. 5-3-49 Idle micro switch lever
If found defective in above checks 1) and 3),
check fuel cut solenoid circuit referring to item
“checking feed back system circuits” in p. 5-29.
5-36