Trionic T5.5

Trionic T5.5
Company type	Engine management system
Industry	Automotive
Founded	1993
Founder	Saab
Products	Engine management systems

Trionic T5.5 is an engine management system developed by Saab as part of their Trionic lineup. It governs ignition timing, fuel delivery, and turbocharger boost pressure. This system was first implemented in the 1993 Saab 9000 2.3 Turbo models equipped with the B234L and B234R engines.

Modifications

Several updates have been introduced since 1994:

1995: Introduction of a four-wire oxygen sensor and electronic heating plates in the intake manifold, except in US and Canadian markets. The K-line communication is routed through the Vehicle Security System (VSS) to allow immobilizer functionality in specific regions. Vehicles with automatic transmissions feature a vacuum pump supporting the brake servo system, with partial regulation by Trionic.
1996: Implementation of OBD II diagnostics for US and Canadian models, requiring dual lambda sensors.
1996.5: EVAP system leak detection added to the OBD II-equipped variants.
1997: Removal of intake manifold heating plates.
1998.5 (Saab 9-3): The K-line is connected via the Main Instrument Unit (MIU), enabling immobilizer control through TWICE (Theft Warning Integrated Central Electronics), except in software for US and Canadian markets. The fuel pump relay receives power from the main relay. Air conditioning request signals are sourced from the MIU. Electrical preheating for the oxygen sensor is powered by the main relay. Vehicles with manual transmissions have a slightly increased requested boost pressure. For OBD II versions, a SID message alerts when an EVAP system leak is confirmed.
1998: Introduction of two new engine variants, B204R and B204E. The B204E engine, available only with manual transmissions, requires high-octane fuel to achieve its rated torque and lacks boost pressure control; it was not offered in US or Canadian markets. Swedish-market vehicles equipped with the B204E engine include OBD II diagnostics and an On-Board Refuelling Vapour Recovery (ORVR) system designed to prevent fuel vapors from escaping into the atmosphere during refueling.

Overview

The ignition setup in Saab Trionic systems features an ignition cassette containing four individual ignition coils, each dedicated to a single spark plug. This capacitive ignition design employs the spark plugs themselves as sensors to monitor combustion quality and detect pre-ignition or knocking events. Consequently, traditional camshaft position sensors and knock sensors are rendered unnecessary. This approach also facilitates accurate misfire detection, meeting OBD II regulatory requirements. Fuel injection operates on a fully sequential basis, regulated by Manifold Absolute Pressure (MAP) readings. Boost pressure management on L and R engine variants is controlled via a solenoid valve that pneumatically actuates the turbocharger wastegate.

This technology has been installed on the Saab 900, Saab 9000, and Saab 9-3 models, with data being most precise for the Saab 900.

Fuel Injector Valves

The injectors utilize solenoid-operated valves featuring a needle-and-seat design. Activation occurs when current energizes the injector coil, opening the valve; deactivation allows a robust spring to close it promptly once current ceases. To optimize combustion efficiency and reduce emissions, each injector is designed with four precisely positioned holes that ensure even fuel distribution. Two of these jets are aligned on the rear side of each intake valve, demanding secure mounting of the injectors. To maintain stability, injectors are paired and held firmly by specialized retainers positioned between cylinders 1–2 and 3–4. Electrical power for injectors is supplied via the main relay, while grounding is managed by the ECU.

Pre-injection

Upon turning the ignition on, the main relay along with the fuel pump relay are energized for a brief period. Once the ECU receives the cranking signal from the crankshaft sensor, it triggers a simultaneous fuel injection through all four injectors, adjusted according to coolant temperature, to facilitate a rapid engine start. If the engine is started but then turned off shortly afterward, a new pre-injection cycle will commence after the ignition remains off for 45 seconds.

Injection time calculation

The ECU determines the necessary fuel quantity for each intake runner by calculating the mass of air drawn into the cylinder. This process incorporates the cylinder volume—0.5 liters per cylinder in the B204 engine—which contains an equivalent volume of air with a specific density and mass. Air density is derived from measurements of absolute pressure and temperature within the intake manifold. After establishing the air mass for combustion, this value is divided by 14.7 (the stoichiometric air-fuel ratio for gasoline) to find the fuel mass required per combustion event. Knowing both injector flow rates and fuel density (stored as preset parameters), the ECU computes the injection duration.

Feedback from oxygen sensor 1 allows adjustment of injection timing to maintain stoichiometric combustion. During strong acceleration, lambda correction is overridden, enabling Wide Open Throttle (WOT) enrichment to maximize power output. Opening the throttle triggers acceleration enrichment (referred to as accelerationsupprikning in Swedish), while closing it initiates deceleration emaciation (decelartionsavmagring). In cold start and warm-up phases—prior to lambda correction activation—fuel enrichment is based on coolant temperature. Under warm engine conditions and normal battery voltage, injection duration ranges from approximately 2.5 milliseconds at idle up to about 18–20 milliseconds at full torque.

Lambda correction

To ensure proper catalyst function, the air-fuel mixture must be stoichiometric—exactly 14.7 kilograms of air per kilogram of gasoline (Lambda=1). For this purpose, an oxygen sensor is positioned near the front section of the exhaust system. This sensor connects to pin 23 on the ECU and is grounded via pin 47 within the ECU. Exhaust gases flow past the oxygen sensor, which measures oxygen content through a chemical reaction that produces an output voltage signal. When running rich (Lambda below 1), output voltage exceeds 0.45 V; when running lean (Lambda above 1), voltage falls below 0.45 V. The voltage oscillates around 0.45 V as Lambda crosses unity. The ECU continuously adjusts injection timing to maintain Lambda at 1.

The oxygen sensor requires heating to operate effectively; this is achieved by an electrical pre-heating element powered through fuse 38 and the main relay from B+, with grounding provided by pin 50 on the ECU. The ECU estimates exhaust gas temperature (EGT) based on engine load and RPM, disconnecting electrical pre-heating when EGT is sufficiently high. Lambda correction is disabled during the first 640 engine revolutions after startup if coolant temperature exceeds 18°C (64°F) under load conditions between idle and WOT or if it surpasses 32°C (90°F) at idle.

Adaptation

The ECU determines the injection time by considering the manifold absolute pressure (MAP) and intake air temperature. This injection time is then adjusted using a correction factor derived from the primary fuel matrix (referred to as huvudbränslematrisen in Swedish), which depends on both MAP and engine RPM. The reason for modifying the injection duration is that the cylinder’s volumetric efficiency varies with engine speed. A final adjustment is applied through the lambda correction to ensure stoichiometric combustion (Lambda=1). This lambda correction can modify the calculated injection time by up to ±25%. Additionally, the ECU can update the correction factors within the main fuel matrix based on lambda correction feedback, optimizing drivability, fuel efficiency, and emissions when lambda correction is inactive. This process is known as Adaptation.

Pointed adaptation

When the ECU calculates an injection duration of 8 ms but lambda correction extends it to 9 ms due to low fuel pressure, it "learns" this updated injection time. This learning involves altering the correction factor for the specific RPM and load point in the main fuel matrix to reflect the new 9 ms duration. In this scenario, the correction factor increases by 9/8 (+12%). Pointed adaptation can adjust individual points in the main fuel matrix by up to ±25%. Adaptation cycles occur every five minutes and last about 30 seconds. The conditions required for adaptation include an active lambda correction and coolant temperature exceeding 64°C (147°F). During this process, the carbon canister’s ventilation valve remains closed.

Global adaptation

For OBDII-equipped vehicles, global adaptation takes place during driving; in non-OBDII models, it happens 15 minutes after engine shutdown. When operating within a specified load and RPM window (60–120 kPa and 2000–3000 RPM), pointed adaptation is disabled, and instead, all points in the fuel matrix are adjusted collectively via a multiplication factor. Global adaptation can modify points in the main fuel matrix by ±25% (although Tech2 diagnostics indicate ±100%). This adaptation runs every five minutes for a duration of 30 seconds, requiring lambda correction activation and coolant temperatures above 64°C (147°F). Throughout global adaptation, the carbon canister’s ventilation valve remains sealed.

Fuel cut

Fuel cut engages when the throttle is fully closed, engine speed exceeds 1900 RPM, and the vehicle is in third, fourth, or fifth gear—after a brief delay of a few seconds. In vehicles with automatic transmissions, fuel cut operates across all gears. Injectors resume operation once engine speed drops to 1400 RPM.

Fuel consumption measurement

The ECU’s signal wire connected to the third injector also links to the main instrument cluster. This instrument calculates fuel consumption by analyzing injector pulse durations. The measured fuel consumption assists in accurately displaying fuel tank levels and computing average consumption values within the SID system.

Fundamental charging pressure

The fundamental charging pressure serves as the basis for Automatic Performance Control (APC). This pressure is mechanically set by adjusting the actuator’s pushrod located between the actuator and the wastegate. If the fundamental charging pressure is too low, the engine fails to accelerate as expected when the throttle is rapidly opened. Conversely, if it is set too high, a negative adaptation process occurs, preventing the achievement of maximum boost pressure. Moreover, there is a significant risk of engine damage because the system cannot sufficiently reduce boost pressure to prevent pre-ignition or knocking. The target fundamental charging pressure should be 0.40 ±0.03 bar (5.80 ±0.43 PSI). After adjustment, the pushrod must have a minimum preload of two full turns (approximately 2 mm) when connected to the wastegate lever. This preload ensures that the wastegate remains closed when no external force is applied. On new turbochargers, the fundamental charging pressure typically approaches or reaches the upper tolerance limit when this preload is set to two turns. It is critical that this preload never falls below two turns (2 mm). When verifying fundamental charging pressure, it should be noted that pressure tends to drop at higher engine speeds and rise in colder ambient temperatures.

Regulation of charging pressure

The regulation of charging pressure employs a three-way solenoid valve with two coils, pneumatically linked via hoses to the turbocharger’s wastegate, its outlet, and the compressor inlet. The solenoid valve receives electrical power from +54 through fuse 13 and is controlled by the ECU via pins 26 and 2. Control signals are delivered using pulse width modulation (PWM) at 90 Hz for engine speeds under 2500 RPM and 70 Hz above this threshold. This frequency adjustment helps prevent resonance within the pneumatic lines. When pin 2 remains grounded longer than pin 26, boost pressure decreases; conversely, grounding pin 26 longer than pin 2 increases boost pressure. To regulate boost effectively, the ECU first calculates a target boost value based on a predefined matrix correlating RPM and throttle position. At wide-open throttle (WOT), these values are selected to ensure that engine torque meets desired levels.

Charging pressure limitation is activated under one or both of these conditions:

In first, second, or reverse gear, a maximum RPM-dependent boost limit applies. The ECU determines current gear by comparing vehicle speed with engine RPM.
When pre-ignition or knocking is detected, a maximum allowable boost is established based on an average ignition timing retardation across cylinders.

Boost pressure reduction to fundamental levels occurs when one or both of these criteria are met:

The brake pedal is depressed, supplying battery voltage to ECU pin 15.
Specific fault codes are triggered (related to throttle position sensor faults, pressure sensor issues, pre-ignition/knocking signals, or boost control malfunctions), or if battery voltage drops below acceptable levels.

Pressure calculation and adjustment

Once the necessary charge pressure has been determined, it is transformed into a PWM signal that governs the solenoid valve. The ECU then ensures the actual pressure, as indicated by the pressure sensor, matches the desired pressure. If discrepancies arise, the PWM signal is refined by applying a correction factor. This correction factor, known as adaptation, is saved within the ECU's memory and consistently incorporated into PWM signal calculations. The objective of this process is to quickly align the actual pressure with the target pressure following any load changes.

Ignition cassette

The red ignition cassette employed in Trionic 5 is positioned on the valve cover directly above the spark plugs. It contains four ignition coils or transformers, each with a secondary coil connected straight to a spark plug. The cassette receives battery voltage from the main relay (B+) and is grounded at a designated earth point. Upon activation of the main relay, the battery voltage is converted to 400 V DC, which is stored in a capacitor. This 400 V supply feeds one terminal of the primary coil in each of the four spark coils. Four triggering wires from the Trionic ECU connect to the ignition cassette at pins 9 (cylinder 1), 10 (cylinder 2), 11 (cylinder 3), and 12 (cylinder 4). When the ECU grounds pin 9, it grounds the primary coil for cylinder one via the cassette’s B+ input, causing up to 40 kV to be induced in that cylinder’s secondary coil. This mechanism similarly controls ignition timing for the other cylinders.

Ignition control

At engine start, ignition timing is set at 10° BTDC. To aid starting when coolant temperature falls below 0°C, the ECU grounds each trigger line at a frequency of 210 times per second between 10° BTDC and 20° ATDC, producing a “multi spark” effect. This feature remains active until engine speed reaches 900 RPM.

During idle, a specialized ignition map is applied with typical timing between 6° and 8° BTDC. If conditions such as cooling fan activation cause stalling, ignition timing advances up to 20° BTDC to boost engine torque and stabilize idle speed. Conversely, ignition timing retards when RPM increases. When throttle position sensor detects throttle opening, the ECU exits idle ignition mapping and adjusts timing based on load and engine speed.

Throughout operation, the ignition cassette continuously measures ion currents within each cylinder and signals potential knocking events to pin 44 of the Trionic ECU. This knock detection logic operates entirely within the cassette and adapts to accommodate interfering fuel additives. Since the ECU knows which cylinder fired, it can process knock information via a single input pin. When ion current signals surpass a threshold indicating knock, the ECU initially reduces ignition advance by 1.5° on that cylinder. If knocking persists, further reductions of 1.5° increments are applied up to a maximum of 12°. Should all cylinders require this reduction simultaneously, a slight increase in fuel delivery is added across all cylinders. For knock events occurring at manifold absolute pressures above 140 kPa, both fuel injection and ignition advance maps are adjusted accordingly. If these measures prove insufficient, boost pressure is decreased to maintain optimal performance. In cases where communication between ignition cassette and ECU fails, boost pressure reverts to base levels and ignition timing is retarded by 12° to mitigate knock risk under load conditions.

Combustion signals

The Trionic system operates without a camshaft position sensor, which is typically essential for sequential pre-ignition or pinging control and fuel injection management. Instead, Saab Trionic determines whether cylinder one or cylinder four fires when the crankshaft position sensor signals that both cylinders are at top dead center (TDC). This identification relies on ionization current measurement. One terminal of the spark coil's secondary winding is conventionally connected to the spark plugs, while the opposite terminal is not grounded directly but linked to an 80 V supply. Consequently, an 80 V potential exists across the spark plug gap except during spark discharge. Following combustion, the combustion chamber temperature rises significantly, causing ion formation in the gases, which then conduct electric current. This conduction produces a current through the spark plug gap without generating a spark. Ionization current is monitored in pairs: cylinders one and two form one pair, and cylinders three and four form the other. When combustion occurs in cylinder one or two, the ignition cassette sends a battery voltage (B+) pulse to ECU pin 17; for combustion in cylinder three or four, this pulse is sent to ECU pin 18. If the crankshaft sensor indicates cylinders one and four at TDC and a B+ pulse arrives simultaneously at pin 17, the ECU identifies cylinder one as firing. During engine start-up, since the ECU cannot yet discern which cylinder is under compression, ignition is initiated simultaneously in cylinders one and four, followed by sparks in cylinders two and three after 180 degrees of crankshaft rotation. Once combustion signals are received at ECU pins 17 and 18, ignition timing and fuel injection synchronize with the engine’s firing sequence. Additionally, these combustion signals assist in misfire detection.

Heat plates

Heat plates serve to reduce emissions during engine warm-up by vaporizing injected fuel before it enters the cylinders. This vaporization diminishes the need for extra fuel enrichment in the air-fuel mixture during warm-up, thereby lowering emissions. When starting the engine and coolant temperature is below +85°C, ECU pin 29 is grounded, activating a relay in the engine bay that completes the electrical circuit powering the heat plates. This circuit is safeguarded by a 40 A MAXI fuse. The heat plates deactivate either when coolant temperature exceeds +85°C or after four minutes have elapsed.

To offset increased intake airflow resistance caused by heat plates, engines equipped with them feature a slight increase in charge pressure—approximately +0.2 bar. Consequently, LPT models fitted with heat plates incorporate a solenoid valve designed to elevate boost pressure above standard levels.

If a heat plate malfunctions, drivability issues may arise due to fuel condensation within the intake during cold operation. Engines lacking heat plates compensate for this condensation by enriching the air-fuel mixture.

Activation of heat plates is managed by software that applies various algorithms to control their operation and adjust for intake restriction effects resulting from their installation.

Shift Up lamp

The Shift Up lamp is present in vehicles equipped with OBD II systems and serves to assist drivers in achieving fuel-efficient driving. It receives power from the ignition circuit (+15) and is grounded through pin 55 on the Trionic ECU. When the ignition is switched on, the lamp illuminates for three seconds as a system check. Under typical driving conditions, the lamp activates at a predetermined engine speed during low-load operation. At full throttle, the Shift Up lamp turns on near 6000 RPM. Notably, it remains off when the vehicle is in fifth gear. Additionally, to encourage faster engine warm-up, the lamp illuminates at a higher RPM when the engine is cold.

References

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