Technical Headlights turning on by themselves after a short period

[samks]

Hi everyone,

I recently bought a used Fiat Grande Punto 1.3 MJT (2009). The car came with a remote battery disconnector installed (located next to the fuse box inside, driver side). I later discovered this was used as a workaround for an issue with the lights.

Here's the problem: after turning off the car, the headlights turn on by themselves about 30-60 seconds later and stay on indefinitely, draining the battery. This happens even if I turn off the lights manually using the stalk before switching off the ignition—they somehow override and come back on.

This behavior occurs regardless of:

• The key being in or out of the ignition.
• Whether the doors are open or closed.
• Whether the car is locked or unlocked.

There are no OBD error codes and I haven't noticed any other electrical issues.

I'm wondering whether this is triggered by the BCM going into a sleep mode with something malfunctioning and then the failsafe is lights on?

Any suggestions on how to narrow down the issue?

 

[varesecrazy]

Hi, potentially basic electrical

Look at top of GP SECTION

FAQ : Electrical Gremlin thread

 

[GrandePunto PL]

1 .Yes. Main ground/earth issue. And corrosion in the main fuse/relay box.
2. Some DIY mods in the car (LED lights, phone chargers etc.) done improperly.
3. Faulty modules like AirBag, Blue&Me, Body.
4. Rumors about "follow me home" function (some claim, Grande/Evo has one)...
5. Combination of 1-4 (for example DIY mods + bad "earth" can interfere with "sleep mode" and trick Body Computer into weird behavior).

 

[samks]

There are no DIY mods, Blue&Me not installed, no warning lights, I checked the potential basic electrical issues (scrubed ground connections, checked wiring, checked fuse boxes etc.) and just about everything I could think of, but no luck.

Now I suspect it's a bad BCM because I tried removing the three connectors in the BCM one by one, but the fault happened regardless. The vertical connector seems to be controlling the head lights as they went dark when it was disconnected, but I could hear the internal BCM relay clicking confirming the fault still would happen.

Since there are no problems when the car is running and it only happens when you would expect the BCM to sleep, it further strengthens my suspicion that it's a bad BCM.

Also, I noticed that when the headlights go on by themselves due to the fault, they will turn off briefly if I turn on the radio before turning on again (500-1000 ms later). I'm not sure what to make of this. Maybe the BCM "wakes" briefly?

Any thoughts?

 

[Bartoosh]

Before condemning the BCM I recommend walking through the functionality on eLearn step-by-step. This will specify the components, BCM pins, fuses and earths in play when engaging the headlights as well as advise on diagnosis.

Click here to reveal the main menu for functionality of the 1.3 MJT exterior lighting.

And click here for a list of tips for diagnosis and testing.