Engine Control Module: Description and Operation
ECM INPUTS
Inputs to the Engine Control Module (ECM)
- +30 voltage supply
- +15 voltage supply
- Ground, reference ground
- Crankshaft position sensor
- Manifold absolute pressure sensor
- Intake air temperature sensor
- Engine coolant temperature sensor
- Throttle position sensor
- Oxygen sensor
- [1][2]Ignition discharge module
- Evaporative emission canister purge valve
- Brake light switch
- AC/ACC
- Cruise control
- Vehicle speed
- Diagnostics
- DRIVE position on cars with automatic transmission
- Torque reduction on cars with automatic transmission
ECM OUTPUTS
Outputs of the Engine Control Module (ECM)
- Sensor ground, reference ground
- Preheating, oxygen sensor
- Throttle position sensor
- Manifold absolute pressure sensor
- [1][2]Ignition discharge module
- Injectors
- Boost pressure control valve
- Idle air control valve
- Evaporative emission canister purge valve
- Main relay
- Fuel pump
- Malfunction Indicator lamp (CHECK ENGINE)
- SHIFT UP lamp (certain markets)
- AC compressor
- Engine speed
- Throttle position
- Engine load
- Fuel consumption
- Pressure, intake manifold
OPERATION
Engine Control Module
Saab Trionic principally controls:
- Ignition (by means of the [1][2]ignition discharge module),
- Fuel injection (which is sequential),
- Boost pressure (by means of a solenoid valve).
The Trionic engine control module has a 70-pole terminal and is located at the right-hand A-pillar. When the powertrain is removed, the ECM terminal and its wiring are guided out through the bulkhead partition.
The ECM has a 32-bit processor which can perform 2 million calculations per second.
A number of sensors supply information to the ECM, which processes these using matrices which have been stored in the ECM after engine operation has been optimized. Examples of such important matrices are ignition timing matrices, fuel matrices and boost pressure matrices.
The ECM is programmed for the B204L and is only to be used for this engine in the Saab 900.
The ECM may be damaged by electrostatic discharges or shorting of any of the ECM's outputs, and great care must therefore be taken whenever handling the ECM, for example in fault diagnosis, e.g. with a break out box.
The engine control module is continuously supplied with +30 voltage and loses adapted values and diagnostic trouble codes stored in its memory if this voltage disappears.
The ECM is adjusted for a voltage between 8 and 16 V during driving.
When the ignition is switched ON, the ECM is activated and pre-injection takes place provided certain conditions are met. The ECM then waits for pulses from the crankshaft position sensor.
The main measured quantity for fuel injection comes from the manifold absolute pressure sensor.
There are substitute functions for all sensors apart from the crankshaft position sensor.
After the ignition has been switched OFF, all sensors which are supplied with 5 V remain activated for 15 minutes. During this time it is also possible to carry out scan tool diagnostics. After 15 minutes, global adaptation of the main fuel matrix takes place and only the memory is then activated.
Adaptation is important for performance, driveablity, fuel consumption and emissions. The ECM must therefore not be unnecessarily disconnected or in any other way de-energized.
ECM Power Supply
+30 voltage is supplied from maxi fuse 2 to the main relay, fuel pump relay and fuse 28. From fuse 28 voltage is supplied to ECM pins 1 and 48.
The ECM uses +30 for its memory. The engine does not start without +30.
+15 voltage is supplied from fuse 17 to ECM pin 60. When +15 is applied to pin 60, the ECM is activated, the main and fuel pump relays operate and all the injectors are activated for pre-injection dependent on engine temperature. The engine will not start without +15.
Manual/Automatic Programming
The Saab Trionic ECM has the same part number for cars with manual and automatic transmission.
When pin 14 is energized through a position other than P or N being selected, the ECM is programmed for a car with automatic transmission.
On cars with manual transmission, the circuit to pin 14 is open.
Ground
At grounding point G7P, the ECM is grounded on pins 24 and 25. The [1][2]ignition discharge module is also grounded at grounding point G7P.
The engine will not start without ground.
Sensor Ground
The crankshaft position sensor, intake manifold pressure sensor, intake air temperature sensor, engine coolant temperature sensor and the throttle position sensor are grounded from ECM pin 67. The leads to the crankshaft position sensor the power lead from the oxygen sensor are also screened from ECM pin 67. The engine will not start without sensor ground.
Reference Ground
On pin 66 the ECM receives reference ground from the sensor ground lead so that it can measure the engine coolant temperature with particularly great precision. Driveablity problems while the engine is warming up will occur if reference ground is not connected to pin 66.
The main instrument uses the sensor ground lead as a reference ground so that it can measure the pressure in the intake manifold with particularly great precision. Pressure cannot be measured if there is no reference ground from the Trionic.
On pin 47 the ECM receives reference ground from grounding point G7S on the engine so that it can measure the voltage from the oxygen sensor with particularly great precision. The malfunction indicator lamp (CHECK ENGINE) in the main instrument lights up if there is no reference ground to pin 47.
Crankshaft Position
The ECM receives information on the position and speed of the crankshaft from the crankshaft position sensor on pin 41.
A perforated disc with 58 ribs is mounted on the crankshaft. The sensor is of the inductive type and is mounted in the crankcase wall of the engine. The distance between the sensor and the perforated disc is within the range 0.4-1.3 mm and is not adjustable.
The sensor acts as a generator and supplies a sinusoidal alternating current. The ECM can determine engine speed by measuring the frequency. Two ribs are missing after the 58th rib on the perforated disc. When rib 1 passes the sensor, the ECM knows that the crankshaft is 117° before top dead center (BTDC).
The voltage from the crankshaft position sensor varies with engine speed. During idling the voltage is 7-10 V (AC) and at 25OO rpm it is approx. 15-20 V (AC). However, it is the frequency and not the voltage which is of interest to the ECM.
The ECM chiefly uses engine speed and crankshaft position to calculate ignition timing, fuel injection timing, fuel injection time and boost pressure and for idle speed control.
Fuel injection is switched off when engine speed exceeds 6200 rpm.
As soon as the ECM receives pulses from the crankshaft position sensor, the ECM grounds the main and fuel pump relays.
If the sensor fails to work or if there is a break in the circuit, the engine will not start.
The sensor resistance is 540 ± 55 Ohms.
Engine Speed Signal
The ECM emits an engine speed signal from pin 58. The signal is a pulse train which varies between 0 and Batt+ and which measures approx. 30 Hz during idling and approx. 85 Hz at 2500 rpm. This corresponds to 2 pulses per crankshaft rotation.
The engine speed signal is used by the main instrument, the clutch control module and the automatic transmission control module.
If the engine speed signal is shorted to ground, the engine can be started but will stop a short time afterwards.
DIAGNOSTICS
The Trionic ECM communicates with an Intelligent SAab Tester (ISAT) scan tool via pin 33. The communication is two-directional and thus involves both input and output signals.
The ISAT scan tool can communicate with Trionic with the ignition switched ON and the engine running, but also for 15 minutes after the engine has been switched OFF. Obviously no functions requiring a +15 or +54 supply can then be activated.
When the engine is running, the diagnostics function has low priority in the Trionic ECM. Trionic therefore breaks off contact with the ISAT at high engine speeds.
The ISAT display shows "NO CONTACT", and Trionic has to be reselected if communication is wanted.
The fault memory of the Trionic ECM is erased if the ECM is de-energized.
Flashing codes
In order to comply with current legal requirements in the US market (OBD I), it must be possible to read off emission-related faults via flashing codes on the malfunction indicator lamp (CHECK ENGINE).
After the ignition has been switched ON and the lamp test has been performed (3 seconds), flashing codes are automatically activated if faults are stored in the memory.
For a list of flashing codes, see "Diagnostic Charts" at "Computers and Controls, System Diagnosis".