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Fiat Stilo 1.6: Engine Controller Issues (IAW 5NF T9) - Car Security Failure, P1120/P1121 Errors

sylwo1962 22989 12
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  • #1 17149024
    sylwo1962
    Level 16  
    Posts: 333
    Help: 5
    Rate: 36
    I bought a used IAW 5NF T9 engine driver cleaned. After installing and attempting to start the car, the engine failure lamp lights up, the message "Car security failure" on the display. After connecting via ELM 327, it saved an atmospheric sensor error, P1120 P1121 and a pending lambda probe error. I called the seller with this problem, he said it was normal. After clearing the errors, the car fired, and for a few days it was ok. A few days ago the same situation happened, the first time I tried to start it stilo. The second time it fired up normally and it's been several days now. The seller complains that the driver is certainly functional, comes from the car after the accident and apparently nothing has happened before. The previous driver that was in my Stilo was, IAW 5NF T1, this one is IAW 5NF T9. Apparently they are interchangeable. I can give this driver back. I do not know what to do.
    .
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  • #2 17149341
    Ireneo
    Level 42  
    Posts: 7818
    Help: 746
    Rate: 2453
    Give up. These reins break down. Apparently nothing happened and the guest is also complaining ... ???
  • #3 17149432
    tolo
    Level 35  
    Posts: 3093
    Help: 231
    Rate: 1168
    Or properly fix the driver.
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  • #4 17149623
    E8600
    Level 41  
    Posts: 8867
    Help: 525
    Rate: 2475







    If the driver was not transferred from the engine for a long time, it is probably cold February on the connector (quite popular in this model). If you can solder, you can fix it yourself. Of course, you're talking about your old man, if he is not completely dead, he is sowing errors.

    By the way, I will ask what colleague has a vintage year and whether the car does not rust? How much LPG does it burn?
    I am asking because I am looking for but for a long time nothing is sensible. :(
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  • #5 17151503
    sylwo1962
    Level 16  
    Posts: 333
    Help: 5
    Rate: 36
    2003. No rust. Petrol. 9l on average
  • #6 17153387
    daro30elektro
    Level 14  
    Posts: 78
    Help: 8
    Rate: 30
    The problem of cold solders is not the main problem of these drivers but their PCB (three path levels) and the BGA connection. As for the software version, IAW5NF.T1 is for the hatchback version and IAW5NF.T9 for the estate version. Soft has a slightly different torque matching the weight of the car.
  • #7 17156358
    sylwo1962
    Level 16  
    Posts: 333
    Help: 5
    Rate: 36
    I mean, they are not interchangeable.
  • #8 17156546
    daro30elektro
    Level 14  
    Posts: 78
    Help: 8
    Rate: 30
    You can change it and the car will work properly just a little differently it will accelerate and that's it.
  • #9 17157005
    sylwo1962
    Level 16  
    Posts: 333
    Help: 5
    Rate: 36
    Is there any difference in strength?
  • #10 17157380
    daro30elektro
    Level 14  
    Posts: 78
    Help: 8
    Rate: 30
    If you ask about PCB design, they don't differ from each other, they just have another program uploaded. Unfortunately, hitting these drivers after so many years in good condition borders on a miracle. Only the use of drivers with Punto or Panda 1.2 IAW5NF.XX HW104 is still sensible with because of their installation in these cars, originally with the side of the battery, not like in Stilo or Doblo on the engine. You only need to lose the software and convert the board because these drivers have two power terminals to control the coils, and Stilo and Doblo have four ignition coils.
  • #11 17157740
    E8600
    Level 41  
    Posts: 8867
    Help: 525
    Rate: 2475
    Sometimes the cause of errors is a frayed electrical harness under the battery. This is another common ailment of this model.
    As for the computer, if someone has conditions, they can flood the PCB with flux and bake so that February can "regenerate".
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  • #12 17878766
    Anonymous
    Level 1  
  • #13 18568398
    Fezzy
    Level 12  
    Posts: 76
    Help: 3
    In the network I found an ad in which someone offers soft at a price of 20 euros.

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Topic summary

✨ The discussion revolves around issues with the Fiat Stilo 1.6's engine controller (IAW 5NF T9) after a used unit was installed. The user experienced a "Car security failure" message and error codes P1120 and P1121 related to the atmospheric sensor, along with a pending lambda probe error. After clearing the errors, the car initially started but later exhibited similar problems. Responses suggest potential causes such as cold solder joints, frayed electrical harnesses, and the interchangeability of engine controllers (IAW 5NF T1 vs. IAW 5NF T9). Some participants recommend proper repairs or using alternative controllers from other Fiat models, while others note that the software differences may affect performance. The conversation highlights the challenges of maintaining older electronic components in vehicles.
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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

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.
  1. Open the ECU and expose the PCB carefully.
  2. Flood the PCB with flux and bake to let solder “regenerate.”
  3. 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]
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