[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. ECM
2. Coupler (Connected to ECM)
3. Oxygen sensor
4. Sealed wire
5. W (White) lead wire
6.
I3
(Black) lead wire
7.
Br/B
(Brown/Black) lead wire
8.
Cancel switch
9.
“CHECK ENGINE” light
10. Ignition switch
(ON)
11. Battery
12.
Mileage sensor
115
'
L----J
A
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.
0
intake system is leaky or air/fuel mixture is too lean due to malfunction
of carburetor,
0
Inner resistance of voltmeter is too small.
0
Oxygen sensor is defective.
Indicates about 0.8V and does not
deflect.
0
Choke is operating because engine is not warmed up fully.
0 Thermal switch is defective.
0 Wide open micro switch is defective.
0
Lead wire of mixture control solenoid is disconnected.
0 Mixture control solenoid valve is defective.
5-33
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