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157 Posts
Discussion Starter · #1 ·
maybe someone can help me. Four years ago i bought a 99 coupe, it was an official european export model. This coupe had in the options menu an item where you could disable / enable the twilight-sensor.

Last year a brandnew 99 Hardtop coupe was offered to me and I traded my coupe for that FRC. This FRC is a US model (the FRCs and the succeeding Z06s were never officially sold in Europe).

The FRC has in the options menu the same item (disable/enable twilight sensor) as my export coupe, but that item has no effect. The twilight sensor is always active and cannot be disabled. My dealer is obviously overcharged - he has no idea how to switch off the twilight sensor.

Does someone know a trick to get rid of that damn sensor?

7 Posts
Reply to twilight sensor

Let me know what you find out on tricking the sensor.

I have a 2000 vette coupe sold new in Canada and mine is the same way.

Dealer and another guy I know say the only way to change it is to replace the BCM. It's locked into the firmware from the factory and you need a different one to fix it.

Not sure if that is right, but let me know what you hear and I will check back to see other posts on this.

97 Posts
Our Canadian cars have no option in the DIC to turn off the twighlight sentinal. Here are two methods on how to do it. I used this second method as I could do it at home in under 10 minutes. :cheers:

Anyone who owns a vette in or from Canada knows that we cannot disarm the "twilight Sentinel" on the DIC,..... But I found the code that needs to be deactivated on the BCM, it will only take your dealer 5 min. to do, then you can turn the "twilight sentinel" ON and OFF as you like. I had it done today!!!! this is what needs done:
go to your dealer, and have them hook a "tech 2" to your vette "it is handheld"
go to options, it will ask if the car has the "RPO Z49" yes or no (canadian vettes are the only ones with this RPO)
enter "no"
Next it will ask if you have options:
Real time Damping
active handling
auto headlamp control
etc. (there are 6 options it asks for) enter yes to the option you have, hit save, exit. your done.!!!!
then go to your DIC, go to "options"
select "twilight on " hit reset, and it is off!!!!!!!!!!!

The Question of How One Can Disable the Twilight Sentinel on Canadian Model C5s comes up quite regularly on the forum and while many people may be aware that it can be done simply by substituting an electrical resistor for the ambient light sensor located in the left hand side of the C5's defroster grill, there nevertheless often appear to be questions about EXACTLY what resistor values to use, EXACTLY what might be involved in doing the job/what kind of PROBLEMS, ISSUES, CONSIDERATIONS one might encounter, etc.
Well, an hour or so ago I just finished 'doing mine' and I thought that it might prove helpful to others who might want to do the same thing by describing EXACTLY how I did it
So, for the record, here's the scoop:
It turned out to be VERY easy to do. The only minor difficulties I encountered were:
a) due to the limited distance I could pull the sensor and its lead from the wiring harness out to facilitate working on it (about 4"), and

b) the fact that one has to work in fairly close quarters down low at the base of the windshield. To make this easier, I moved the seat(s) as far forward as possible when actually doing the work.

Following information obtained on the forum, I did it as follows:

1. I used a CREDIT CARD to 'work'/loosen and 'pop out' the dash top defroster grill..

2. The Twilight Sentinel (TS) sensor itself comes in a base/housing that plugs into a female socket on the left hand underside of the defroster grill. It simply screws into its defroster grill socket, requiring only a 1/4 clockwise turn to 'lock' it into place like (eg.) a tail light bulb into its socket.

3. Before I did ANYTHING (even unscrewed the sensor from the grill), I tied some *black* fishing line (about 4 feet worth) around the ACTUAL WIRE connecting the sensor to the harness, ***JUST IN CASE the whole thing should accidentally slip down into the dash during the process***, so I could pull it up again... (THAT WOULD BE A PAIN - the head lights would then ALWAYS be on when the car was running, and trying to fish it out again looked like it would NOT be easy...).

4. I THEN unscrewed the sensor from the defroster grill.

5. THEN, the sensor itself simply plugs into a male connector on the end of the wiring harness lead, so I unplugged the sensor from its harness connector. (I used a small jeweller's screwdriver to release a clip to allow the parts to be separated).

6. I then reinstalled the (now disconnected) sensor back into the defroster grill (for 'looks' only, since it's now non-functional),

7. Next, I bent the leads on a 4.7K OHM ½ Watt resistor that I picked up today (6-pak for $1.49; needed only one), and plugged the resistor leads into the contacts on the end of the male wiring harness connector. (Real nice fit - tight but not too tight).

8. I then taped the resistor/connector up to prevent shorts and provide further insurance against them coming apart, using black electrical tape.

9. I then ***taped the connector to the sensor housing*** , the objective being to help ensure that it wouldn't flop around/rattle/make noise if simply left loose.

10. I then looped and tied the fishing line through a couple of bars in the defroster grill, leaving only about 4" of slack to its tie point back on the wiring harness, and cut off the surplus line with scissors - JUST IN CASE THE ELECTRICAL TAPE SHOULD EVER SOFTEN/COME LOOSE FROM HEAT IN THE CAR and the resistor/lead might decide to separate from the sensor and drop down into the dash as mentioned above and cause noise/be difficult to retrieve...

11. I then reinstalled the defroster grill and 'voila'.

157 Posts
Discussion Starter · #4 ·
Yiippii!! I disabled that f... sensor now!!
I got a Tech II this morning and I did exactly what you were posting, blownz06 (go to options of the BCM, say no to "RPO Z49", saving etc.)
And I can switch off the light now when the flatfoots are after me at night (you know - too loud, too fast - what ever) !

39,959 Posts
Way to go blownz06. Tremendous info:thumbsup:
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