Typical Fiat 500L components
At the heart of the 500L’s engine management system is the bulkhead-mounted Bosch ECU, secured to the vehicle with shear bolts which must be drilled out in order to remove the ECU. The ECU has two connectors held in place with lock tabs.
Ahead of the ECU is this Bosch diesel particulate filter differential pressure sensor, incorporating a piezo-resistive sensor element. It assesses the pressure difference across the filter, in turn calculating the filter’s load status, used to determine/trigger regeneration. The glow plug or glow control unit (GCU) is also bulkhead-mounted, and its function is to monitor and control the glow plugs in an open loop. It has to be a tough unit to cope with high underbonnet temperatures, vibration and electromagnetic interference. The four fuel injectors are relatively easy to access at the top of the engine. Problems can arise when it is time to remove an injector, due to potential seizing of the injector in the cylinderhead. Specialist assistance may be required. This is one of the four glow plugs, essential for efficient cold starting. They are found towards the rear of the engine and are somewhat inaccessible. As with the fuel injectors, seizure within the cylinderhead is possible – attempt removal with great care.
The high-pressure fuel pump (rear of engine, right-hand side), is an essential part of the Multijet II diesel set-up, receiving its fuel from a small pump in the tank. In turn, the timing belt-driven high-pressure pump continuously feeds the fuel rail. The battery in the 500L has to cope with the demands of an engine stopstart system. As with an increasing number of modern cars, it is essential for effective operation that the correct specification of Enhanced Flooded Battery (EFB) is used. Incorporated within the negative (ground/earth) battery connector is a battery monitoring system, used by the ECU to aid stop-start operation by relaying battery condition to the ECU. A clean terminal/contact is essential here.
The underbonnet fuse/ relay box is positioned just inboard of the left-hand front inner wing, behind the headlamp and next to the battery. It is imperative that moisture is not able to enter the box; check that its plastic cover is fully/correctly engaged.
The combined throttle body/egr (exhaust gas recirculation) valve assembly plays a vital role in engine operation. The ECU transfers pedal position data to the throttle body, which incorporates a potentiometer, which in turn advises throttle position to the ECU.