Front fog tell-tale

[vino92]

Hi, I have a 2009 TC and I’m wondering if there is anyway of getting the front fog tell-tale in the instrument cluster to activate when the switch is pulled using forscan. I’ve checked the IC module in forscan, but unfortunately, to change it, it must be in the AS BUILT section, and I’m struggling to figure out what one would need changed. I’ve already got the factory switch and bumper with the fog lights installed, and wired it up so they work, but the tell-tale doesn’t activate. Help would be greatly appreciated. Thanks in advance.

[lowspeedpursuit]

The "correct" answer is to find a TC identical to yours in every way except having factory front fogs, run the VIN through https://www.motorcraftservice.com/AsBuilt/, and determine which half-byte is different.

 

The other way is trial-and-error, making extremely sure to back up anything before you change it. Forscan will sometimes report a failure to write if you try to change something that can't be changed. You also can't necessarily assume the byte you want lives in IC. Per my manuals, the GEM is also involved in fog light operation.

 

Dicking around with it just now, the 9th digit in the first GEM address, 726-01-01, has an effect on my rear fog indicator. I have rear fogs only (front were apparently not offered in US 2010) and my stock value is 9. A junkyard 2011 listing front fogs shows a stock value of D. Setting my value to D doesn't seem to change how the indicator functions, but setting it to 0 forces it to stay on permanently.

 

If yours is also 9 now, setting it to D is the first thing I would try. Otherwise, you'll need to keep playing around with it.

 

If you're not already familiar with how AS-BUILT works, the last byte in every address functions as a checksum calculated by adding together the values of all other bytes, plus the address with a leading 0, and discarding any overflow. So, since 9x -> Dx means adding 4, you need to add 4 to the first half-byte of the checksum as well. Forscan will also fail to write if you get this wrong.

 

I doubt I can help you any more precisely than that. My 2010 cluster doesn't even seem to have a front fog indicator I could try to activate.

 

Edited June 8, 2023 by lowspeedpursuit
correction