4B•2 Emissions control systems
The sensor output voltage alters in a large step
at this point, the ECU using the signal change
as a reference point, and correcting the inlet
air/fuel mixture accordingly by altering the fuel
injector pulse width (injector opening time).
Exhaust gas recirculation system
This system circulates a proportion of the
exhaust gas back into the combustion
chambers during certain operating conditions,
in order to reduce harmful exhaust gas
emissions. This is achieved by effectively
reducing the peak temperatures reached in
the combustion chambers by the introduction
of the inert exhaust gas. Two systems were
fitted - a mechanical system, and an electronic
system controlled by the LH-Jetronic ECU.
If a fault occurs in the EGR system, the
"CHECK ENGINE" warning light on the
instrument panel will be lit, and the
corresponding fault code will be stored in the
Evaporative emissions control
To minimise the escape into the atmosphere
of unburned hydrocarbons, an evaporative
emissions control system is fitted to certain
models. The system is referred to as the
"evaporative-loss control device" (ELCD). The
fuel tank filler cap is sealed, and a charcoal
canister is mounted on the front right-hand
side of the car beneath the right-hand wing, to
collect the petrol vapours generated in the
tank when the car is parked. The vapours are
stored until they can be cleared from the
canister (under the control of the fuel system
ECU via the purge valve, into the inlet tract, to
be burned by the engine during normal
To ensure that the engine runs correctly
when it is cold and/or idling, and to protect the
catalytic converter from the effects of an over-
rich mixture, the purge control valve is not
opened by the ECU until the engine has
warmed up, and the engine is under load; the
valve solenoid is then modulated on and off, to
allow the stored vapour to pass into the inlet
A deceleration dashpot (or "throttle
damper") is fitted to the throttle lever on the
throttle housing on some models. Its purpose
is to control the deceleration of the engine
during overrun, in order to prevent the
emission of unburned hydrocarbons. If the
accelerator pedal is released with the engine
running at a speed of 3000 rpm, the engine
should take approximately 4 seconds to
decelerate to a speed of 875 rpm.
Automatic idling control (AIC)
Some models are fitted with an automatic
idling control system, which provides
smoother idling, improved cold and warm-up
running, idle speed compensation (to allow for
the operation of the air conditioning
compressor, alternator or power steering
pump), and engine deceleration control.
The AIC valve controls the flow of air
bypassing the throttle valve. The valve is
operated by the ECU.
Some models have a pulse-air system,
which supplies air to the downstream side of
the exhaust valves, in order to complete
oxidation of any unburned hydrocarbons
present in the exhaust gases. The system uses
the pressure pulses in the exhaust manifold to
draw the air from the air cleaner.
Secondary air injection
On this system, air is injected into the
exhaust manifold before the lambda sensor
and catalytic converter have reached working
temperature, in order to assist in the
combustion of hydrocarbons. The system is
activated when the engine is started, and its
running time depends on the engine
temperature and the point when the lambda
sensor begins to operate.
Crankcase emissions control
1 The components of this system require no
attention, other than to check at regular
intervals that the hose(s) are clear and
2 If a fault occurs in the EGR system, a fault
code is stored in the LH-Jetronic ECU, and a
warning light is lit on the instrument panel.
Check all wiring and hose connections on the
EGR valve for security. If this does not rectify
the fault, the advice of a Saab dealer should
Removal and refitting
Air temperature sensor
3 To remove the inlet air temperature sensor,
disconnect the wiring and unscrew the sensor
from the inlet manifold. Refitting is a reversal
4 The vacuum tank is located on the left-hand
front of the engine compartment. First, remove
the airflow meter as described in Chapter 4A.
5 Disconnect the vacuum hoses, and remove
the vacuum tank together with the mounting
6 Remove the mounting bracket, and fit it to
the new vacuum tank.
7 Refitting is a reversal of removal.
8 The timing valve is located in the line
between the vacuum tank and the EGR valve.
9 Disconnect the wiring and the hoses, noting
their location, and remove the valve.
10 Refitting is a reversal of removal.
11 The lambda sensor may be tested with a
multi-meter by disconnecting the wiring at the
connector, either near the right-hand end of
the inlet manifold (models with LH-Jetronic
system) or on the right-hand side of the
bulkhead (models with Trionic system).
12 Connect an ohmmeter between terminals
1 and 2 on the sensor wiring plug. Do not
connect the ohmmeter to the ECU wiring. The
resistance should be between 2.9 and 4.0
ohms for a 12-watt lambda sensor (unleaded
petrol), or approximately 2.1 ohms for an 18-
watt lambda sensor (leaded petrol and turbo
class 1). The resistance varies with
temperature, and can be as high as 10 ohms.
13 Reconnect the wiring after making the test.
Note: The lambda sensor is DELICATE. It will
not work if it is dropped or knocked, if its
power supply is disrupted, or if any cleaning
materials are used on it. The sensor should be
renewed every 60 000 miles/90 000 km.
14 Disconnect the wiring plug at the right-
hand side of the inlet manifold.
15 Unclip the wiring from the cylinder head,
and feed it through to the front of the engine.
16 Remove the weatherstrip and cover from
the false bulkhead at the rear of the engine
compartment. Lift the right-hand part of the
cover, and disconnect the lambda sensor
17 Unscrew the screws from the bulkhead
plate, then pull the lambda sensor wiring to the
front of the engine compartment, lifting the air
conditioning pipe where necessary.
18 Where necessary, release the wiring from
the clamp on the coolant pipe, and unscrew
the wiring support bolts as necessary (see
19 Where necessary, release the clip near the
lower air conditioning compressor mounting
20 Unscrew the sensor from the exhaust
system downpipe, and remove it. The sensor
may be tight, in which case it will help if it is
turned back and forth on its threads as it is
being removed. Note that it is possible to
obtain a special slotted socket, which locates
on the sensor without causing any damage to
21 Refitting is a reverse of the removal
procedure. Prior to installing the sensor, apply
a smear of high-temperature grease to the
sensor threads. Tighten the sensor to the
specified torque (see illustration). The wiring
must be correctly routed, and in no danger of
contacting the exhaust system.