ECU) series Fiat IAW 5AF with HW303 hardware have been common in Fiat gasoline models since the late 1990s and early 2000s. They are mainly used on low-volume engines with ignition coils controlled directly by the computer. Despite their good functionality, these modules have characteristic and recurrent defectwhich often leads to loss of cylinders and serious damage to the ECU itself.
Fiat ECU models IAW 5AF (HW303)
| ECU model | Hardware | Manufacturer |
|---|---|---|
| IAW 5AF.P3 | HW303 | Magneti Marelli |
| IAW 5AF.P4 | HW303 | Magneti Marelli |
| IAW5AF.P3 | HW303 | Magneti Marelli |
| IAW5AF.P4 | HW303 | Magneti Marelli |
Note: spelling may vary, but hardware modules are identical.
Main problem and failure mechanism
The most common problem with these ECU computers is loss of one or more cylinderswhich occurs as a consequence of short circuit in spark plug coil. When the coil starts to fail, it creates an unstable load on the output drivers of the computer.
As a result detonations and misfiresthat cause the ECU to feed higher current to the coils. This additional load flows through the output terminals of the computer and results in overheating and internal oscillation the control transistors or tracks on the circuit board.
Very often the problem is aggravated after ECU partial repairwhere only the electronics are restored without removing the root cause - the defective coil.
Typical symptoms and consequences
| Problems | Description |
|---|---|
| Loss of cylinder | One or more cylinders stop working |
| Detonations | Uneven combustion and misfires |
| Increased current | ECU draws more current to the coils |
| Shortening in the ECU | Failure of drivers and output channels |
| Repetitive failure | The problem returns if the coils are not replaced |
Important conclusion
It is crucial to understand that repairing the ECU without replacing the defective coils is a temporary solution. If after rebuilding the module it is installed back with the same coils, the failure will almost certainly recur. This leads to additional costs and the risk of irreversible damage to the computer.
Testimonial
In the diagnosis and repair of Fiat IAW 5AF (HW303) always should:
to check all coils,
to measure their resistance,
and when in doubt be replaced necessarily.
This is the only way to ensure long-lasting and reliable operation of the ECU module.
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