FAQ
TL;DR: Stilo 1.6 ECU swaps: Panda/Punto 1.2 IAW5NF HW104 units use two coil drivers vs Stilo’s four, and “they just have another program uploaded.” Best fix: reflash Stilo software and adapt coil outputs, or seek a sound T1/T9. [Elektroda, daro30elektro, post #17157380]
Why it matters: This FAQ helps Fiat Stilo 1.6 owners fix “Car security failure” and P1120/P1121 after ECU changes, with proven donor and repair options.
Quick Facts
- IAW5NF.T1 = hatchback, IAW5NF.T9 = estate; same PCB design, different torque-mapped software. [Elektroda, daro30elektro, post #17153387]
- Main failures: multilayer PCB and BGA connections; cold solder joints are secondary. [Elektroda, daro30elektro, post #17153387]
- Viable donor: Panda/Punto 1.2 IAW5NF.XX HW104; reflash Stilo software and adapt coil drivers (2 vs 4). [Elektroda, daro30elektro, post #17157380]
- Intermittent throttle/start faults can come from a frayed harness under the battery. [Elektroda, E8600, post #17157740]
- Stilo IAW 5NF flash files are advertised online at approx. €20. [Elektroda, Fezzy, post #18568398]
How do I fix "Car security failure" and P1120/P1121 after an ECU swap on a Stilo 1.6?
Focus on the ECU connection and board. On IAW 5NF units, cracked solder at the connector is common. Resolder or reflow can restore stability. An aged ECU can also intermittently throw throttle codes even if it temporarily starts after clearing faults. Check the ECU before chasing sensors. [Elektroda, E8600, post #17149623]
Are IAW 5NF.T1 and IAW 5NF.T9 interchangeable? Will it run right?
Yes. The car will run, though response can feel slightly different because the software maps differ. As one expert put it, “You can change it and the car will work properly.” Expect minor drivability changes rather than incompatibility. [Elektroda, daro30elektro, post #17156546]
Is there any difference in engine power between T1 and T9?
No hardware power difference. The PCB is the same. The difference is the uploaded program, which adjusts torque to vehicle weight. T1 targets the hatchback; T9 targets the estate. Expect mapping differences, not mechanical changes. [Elektroda, daro30elektro, post #17153387]
What typically fails inside the IAW 5NF ECU on the Stilo 1.6?
Primary issues are the three-layer PCB and BGA package connections. Cold solder joints exist but are not the main failure. These age-related faults make good used units difficult to source years later. Consider repair or a compatible donor. [Elektroda, daro30elektro, post #17153387]
How can I DIY a quick reflow fix on an IAW 5NF board?
You can attempt a flux-and-bake reflow to renew cracked joints.
- Open the ECU and expose the PCB carefully.
- Flood the PCB with flux and bake to let solder “regenerate.”
- Reassemble, clear DTCs, and road-test to confirm stability.
“Bake” implies controlled heat; proceed only if skilled. [Elektroda, E8600, post #17157740]
Can wiring under the battery cause throttle or start issues?
Yes. The under-battery harness can chafe, causing intermittent throttle faults and odd starting behavior. Inspect, repair, and re-wrap the loom before replacing sensors. This harness issue is a well-noted Stilo ailment and can mimic ECU failure. [Elektroda, E8600, post #17157740]
Why did I also get atmospheric sensor and lambda pending errors after the swap?
A partially failing ECU can “sow” unrelated sensor errors. That noise disappears after clearing codes, then returns days later. Prioritize ECU inspection and connector resoldering before replacing sensors. This behavior aligns with marginal board or connector joints. [Elektroda, E8600, post #17149623]
What donor ECU is best if my 5NF is failing?
Consider Panda or Punto 1.2 IAW5NF.XX HW104 units. They live near the battery, not on the engine, so they run cooler. You must flash Stilo software and adapt the board, because those units drive two coil outputs while Stilo uses four. [Elektroda, daro30elektro, post #17157380]
Where can I get the correct Stilo 1.6 IAW 5NF software (flash file)?
Flash files are advertised online; one listing cites a €20 download. Verify part numbers and versions match your hardware before flashing. Use a reputable service or specialist to avoid corrupt writes and immobilizer issues. [Elektroda, Fezzy, post #18568398]
Why are good used IAW 5NF ECUs so hard to find now?
Age and heat cycles degrade these boards. As one expert summarized, finding a good one “borders on a miracle.” Consider a professional repair or the Panda/Punto HW104 donor route with proper software and coil driver adaptation. [Elektroda, daro30elektro, post #17157380]
What fuel economy are owners reporting for a 2003 Stilo 1.6 petrol?
One owner of a 2003 petrol Stilo reports about 9 L/100 km in typical use. Treat this as an individual data point, not a factory spec. Use it to benchmark your post-repair results after ECU or harness fixes. [Elektroda, sylwo1962, post #17151503]
My Stilo fails the first start but fires on the second. What should I check?
Intermittent starts often point to wiring or ECU solder issues. Inspect the battery-undertray harness for chafing. If clean, consider a controlled flux-and-bake reflow on the ECU PCB. Verify improvements with a longer test drive after clearing DTCs. [Elektroda, E8600, post #17157740]
Should I return a “cleaned” used ECU that still throws faults?
If faults persist, consider returning it or commissioning a proper repair. A seasoned member’s blunt advice was: “Give up.” These units are failure-prone with age, so insist on a proven, repaired, or testable module. [Elektroda, Ireneo, post #17149341]
Can a Panda/Punto 5NF HW104 be plug-and-play on Stilo?
No. It requires two things: flashing the correct Stilo program and adapting the board for four ignition coils. Those donor ECUs have two coil drivers, versus four on Stilo/Doblo, so modification is mandatory for proper operation. [Elektroda, daro30elektro, post #17157380]
