Help! '94 LT1 "Service Soon" Light Came on Tonight.

[WillC4]

So, i recently had my PCM professionally tuned for the vette. I gave it a good test drive for around 40 miles and the car seemed to run pretty well. My cooling fans are tuned to turn on at 182° and off at 172° to compliment the 160° T-stat. I pulled up into my driveway and felt that my idle RPM was a bit high and then switched on my manual fan switch. I temporarily leave the car to set up the parking space and when i come back, the "Service Soon" light was on. I quickly pulled into the spot and turned the car off, then back on again at the time the RPMs bounced up and down a little bit ( seemed to bounce up and down in 300 rpm increments). I then turned the car off and waited a couple of minutes, then started the car up once again, this time the idle was steady, but the light remained on. I walked to the front and noticed that the both cooling fans were on, so i went in and turned the manual switch off. The temp gage read 163°, so i thought why are the fans still on, they should be off by now. I then shut the car off and unplugged the battery to reset the computer. I started the car again, and now warning light is off now and the fans come on and off automatically like they should be. I suspect that when i turned on my fan switch, it probably shorted the fan relay circuit. Ill be watching it closely for the next few days, but does what i suspect sound like the most likely culprit?

 

[93Rubie]

I would pull the code when the Service Engine Soon light comes on. It will give you something to go off of. Otherwise you are hunting around in the dark for the most part. Let us know.

 

[Hib Halverson]

When certain codes set, the fans will run all the time.

 

[WillC4]

I finally ran the diagnostics and it gave me 1 code:

DTC 24 Vehicle Speed Sensor, Signal too low.

FSM didnt say anything about it kicking the fans on though..

Anyways, it may seem that i will need to replace the sensor. Any thoughts or opinions on what i should do otherwiswe?

 

[toptechx6]

Don't replace anything, run the step by step diagnostic procedure for the code found in book #2 of the FSM, it will lead you to problem. Codes indicate a problem in the circuit, not that a part is bad, it could simply be a bad connection.