: Service soon light

09-12-10, 01:59 PM
My Coupe Deville finally passed it's annual test after about 5 weeks of welding, filling, painting and other bits and bobs :)

Been cruisin' for the last 2 days and what a ride she is :)
The only thing is that when I reach 50mph or above the Service Soon light comes on for a few seconds then goes off for a while and this repeats itself a few times.

No codes are shown. Anyone any ideas?

Edit: scrap the above

I just checked and do get 2 codes, 39 and 52

09-12-10, 03:14 PM
What do those codes come back as? Check the FAQs...

09-12-10, 03:20 PM
What do those codes come back as? Check the FAQs...

what I found was : 52 - ECM reset (battery been disconnected)
39 - TCC Torque converter ...somewhere else I read 39 might be knock sensor

09-12-10, 04:22 PM
The 39 code would make sense to be TCC problem. Think about when your problem is happening: exactly when the torque converter clutch is supposed to engage.

Check THIS SITE (http://myweb.accessus.net/~090/81cfb.html) for your codes.

Check out this procedure to perhaps narrow things down (edit - the formatting is messed up, just scroll to the bottom on the above link):

On cars equiped with an "outside temperature" button on the ECC, ECM operating mode can be switched between closed loop vs. open loop mode by depressing this button. With the LED illuminated ECM operates in a "Closed Loop Mode" - with the LED off ECM is in "Open Loop Mode."

ECM O2 Throttlet TCC output 4th A/C
operating sensor switch input output gear input clutch
mode input input input output
Light on Closed loop Rich Closed throttle TCC enabled In 4th gear A/C Clutch enabled
Light off Open loop Lean Open throttle TCC disabled Not in 4th gear A/C Clutch disabled

09-12-10, 04:32 PM
Thanks for that, much appreciated.

But umm...I'm not sure what a closed loop or open loop means or what happens when the TCC is disabled or enabled?

09-12-10, 04:39 PM
Open loop: car not warmed up. Computer runs on a basic program, not taking information from all sensors.
Closed loop: car warmed up (about 1 min after startup), computer looks at data from all sensors (02, TPS, etc) to determine exact fuel needed to achieve proper mixture for given throttle angle.

TCC: torque converter clutch. This locks the torque converter to prevent slippage while at cruise RPM. Prevents heat in the trans, and boosts mileage.

Do you have the FSM for your car?

09-12-10, 04:44 PM
I have the haynes manual but not the FSM