Chapter 6 Emissions control systems
AFS
side connector
Air flow sensor
side connector
16.2a To check the intake air temperature sensor on 1990 16.2b To check the intake air temperature sensor on 1991
models, measure the resistance between terminals 4 and 6 of the
models, measure the resistance between terminals 5 and 6 of the
air flow sensor air flow sensor
switch has been turned off, the light goes out. And even if the light remains
on, it goes out when the ignition switch is turned off. The next time the igni-
tion switch is turned on, the light doesn’t come back on again unless the
ECU has “memorized” the code(s) it stored the last time you operated the
vehicle, or it detects the malfunction again. The light does, however, come
on for five seconds -then goes out-every time you turn on the ignition
switch, to indicate that the malfunction indicator light circuit is operating
normally.
2 The malfunction indicator light will comes on when any of the follow-
ing components develop a problem:
Air flowsensor
Barometric pressure sensor
Crank angle sensor
EGR temperature sensor (California models)
Engine control unit
Engine coolant temperature sensor
Fuel injector(s)
Fuel pump
intake air temperature sensor
Motor position sensor (2.4L engines)
No. 1 cylinder TDC sensor
Oxygen sensor
Throttle position sensor
3 To check the malfunction indicator light, verify that the light comes on
for five seconds when you turn on the ignition switch. If the light doesn’t
come on, check the indicator light circuit and the light bulb.
4 If the malfunction indicator light comes on -and stays on -when you
start the car, or if it comes on while you’re driving -and doesn’t go off, drive
the vehicle home and discontinue operation until you’ve outputted the
malfunction code(s), identified the problem and fixed it.
5 Any malfunction codes memorized andstored bythe ECU will remain
in its memory even when the ignition switch is turned off, because the com-
puter memory is battery-powered when the engine electrical system is
shut off. But if the battery is disconnected, or the ECU is unplugged,
memory is erased and any codes stored are lost. Because the ECU’s
memory is battery-powered when the engine is turned off, the battery must
be fully charged and in good condition. If battery voltage is low, the ECU is
unable to detect a malfunction or memorize and store a code.
6 To output the malfunction codes, hook up an analog voltmeter to the
self-diagnosis connector as shown (see illustration).
7 Turn the ignition switch to On. The ECU will begin displaying the con-
tents of its memory immediately. fjow refer to the accompanying malfunc-
tion code and diagnosis table (see illustration). If the MPI system is
operating normally and there are no-problems, the needle on the voltmeter
indicates a normal pattern of deflection; in other words, it deflects on and
off at a regular rate -the “on” and “off” segments are equal in duration (see
the “normal state” output signal pattern). However, if the ECU outputs a
malfunction code, the deflection of the voltmeter needle will be long or
short (sort of like Morse code). For example, if the oxygen sensor is mal-
functioning, the needle will make one long deflection, followed by a one
short deflection; if the air flow sensor is bad, the needle will make one long
deflection, then two short ones; and so on.
Intake air
16.3a Heating the intake air temperature sensor on a 1990 model
8 Note that the actual malfunction code number on the accompanying
table is not the same number as the output preference order (far left
column on the chart). That’s because the ECU outputs any stored codes in -
a specific order to simplify your task of identifying each sequence of
needle deflection patterns.
9 After you’ve outputted all stored codes and identified the general
source of the problem(s), go to the next Section, or the indicated Chapter,
check the suspected bad component or circuit and make the necessary
repairs or replace the component.
10 After you’ve fixed the problem, check your work: Repeat the proce-
dure above and verify that the malfunction code for the problem you fixed
is no longer displayed. If the code is still displayed, you haven’t fixed the
problem (or the ECU itself isfaulty, but don’t replace an ECU until you’re
positive that everything in a circuit or system is functioning normally).
11 To erase the ECU’s memory of any stored codes once the problem is
fixed, simply disconnect the negative terminal of the battery for at least 10
seconds.
16 Information sensors (fuel-injected models only)
Intake air temperature sensor
Refer to illustrations 16.2a, 16.26, 16.3a and 16.3b
1 Unplug the electrical connector from the intake air temperature sen-
sor.
2 Measure the resistance between the indicated terminals (see illus-
trations).
3 While heating the sensor with a hair drier (see illustrations), mea-
sure the resistance and note how the resistance
changes as the sen-
sor heats
up. At 32-degrees
F, the resistance should be 6 k-ohms; at
68-degrees F, it should be 2.7 k-ohms; at 176-degrees F, it should be
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