Can anyone help me out, I have had my 93 for two years....the "service engine soon" light has been on all of the time......I pulled the codes and got a code "15" which stands for "low coolant temp". I replaced the coolant temp sensors and it still persists. The overflow line that connects to the radiator overflow tank has got a leak so the tank is always empty. I am going to find a fix for this problem, would this leak produce the code that I am seeing???? it has nothing to do with coolant temp..? Also, when I start the engine I have to let it warm up because it spits and spudders, after a few minutes its fine and runs great.....it is more pronounced in the winter, but still does it in warm weather. If I even touch the gas pedal while starting it....it will flood and take longer to start. Is this false code telling the ECM that it is cold outside and chocks the motor on start-up then when engine temp comes up the chock goes off???thanks,

 

The code 15 (signal voltage low) means that the ECM has seen something out of it's parameter. This is the CTS sensor and circuitry. The CTS is located in the waterpump housing and not the radiator. It is a very important sensor for overall drivability. The ECM is using preset parameters to run the car with the code present. The CTS has two wires going to it. One is yellow and the other is black. The yellow should have 5v with the key on an the black is ground. You would be better off using a FSM to troubleshoot the code. I imagine the car is running rich.

 

Where would I be able to find a FSM to diagnose the problem. I know that my local AutoZone will come out and hook up different diagnostic tools to try and pull codes, would they have this FSM? and what does FSM stand for??

 

I just did a search on FSM, boy do I feel stupid....factory service manual......CTS=coolant temp sensor....duh.. So, the code 15 does not stand for "low coolant temp" ???? My gauges inside show the temps correctly.....?

 

Check and make sure the yellow wire has 5v with the key on. Check and make sure the black wire is a solid ground. Wiggle both wires while testing. If both check out, your sensor is probably bad. Make sure the connector is in good shape and is connected right.

 

This is what the sensor looks like. Make sure to check the connector and test the wiring before replacing it. If not, you might be wasting money on a good sensor.

 

You can ohm the sensor at different temps also. These numbers will get you in the ballpark.

 

thanks abunch....I will try to test tomarrow, I ll let you know.....

 

Could also be a failed t-stat. They take forever to reach operating temp when that happens.

 

CIRCUIT DESCRIPTION:
The coolant temperature sensor is a thermistor used to vary voltage in the reference circuit from the Electronic Control Module (ECM) to the sensor. The ECM applies a 5.0 volt reference voltage at circuit 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, and the ECM will measure high voltage (near reference voltage). As the engine warms, the sensor resistance decreases, current through the sensor increases and the circuit voltage drops. Each voltage value in the reference circuit corresponds to a specific temperature. At normal engine operating temperature (85°C - 95°C/185°F - 203°F) the voltage will measure about 1.5 to 2.0 volts.

Code 15 will set if signal voltage indicates a coolant temperature below -49°C (-56°F).






DIAGNOSTIC AIDS:
A "Scan" tool displays engine temperature in degrees centigrade and fahrenheit. After engine is started, the temperature should rise steadily to about 90°C/ 195°F then stabilize when thermostat opens. A faulty connection or open in circuits 410 or 808 will cause a Code 15. If Code 21 or 52 is also present, check circuit 808 for faulty wiring or connections. Also check connections at sensor and ECM ground connections.

 

I checked the voltage, right on 5 volts all connections look good....where will I find circuit 808?
also, how would I check to see if the black wire is a "good ground". I checked the voltage by putting a voltmeter with the pos prob in the connector pin slot of the yellow wire and the other probe in the black wire pin slot.

 

You can use a test light or volt meter to check the ground. Just do the opposite you would when checking for voltage.

Test light: alligator clip on the pos side of batter and probe the black wire. If it lights up, wiggle it and see if the light stays solid. If both wires check out, check the connector real good. Make sure it snaps into place on the sensor. If it checks out good, replace the sensor. This is easier that using a scan tool, especially if you don't have one.

 

808 is the black wire (sensor ground circuit) from pcm to ECT, TPS and
EOT. Yellow wire is circuit 410, 5 volt reference signal

 

thanks guys, I will look very closely at that connector......maybe replace the sensor tonight and will let you know when I find the problem...

 

Hello,
I have been chasing the DTC15 on my 93 coupe for a few months.
Most cases I guess its the sensor in the water pump, but not for me.

I have logged my car with Datamaster and it never sees the alarm and always shows engine temp above 185. The the car dies and gets SES.

I hope you get lucky. I'll be waiting to see what you found.

I may have finally found out what was wrong but I don't want to say until the new part gets here and I put the car back together and drive it.

 

It's fixed!!!!!!!thanks for all the advise guys......about a year ago I replaced the sensor (in the water pump) because I broke the connector with a wrench doing maintenance. After I broke the connector I got the SES light....so I went out and bought a new sensor and put it in....still got the SES light even after clearing the codes.....that is why I waited so long before replacing the sensor.....it was brand new-but defective....I put the new sensor in this am and to my suprise the engine fired right up and ran smooth with no sputtering or hesitation, and no SES light on the DIC..........I am a happy camper...

 

Glad you got it fixed.

 

Glad it worked out.

Randy

 

t-93.

Congrats on getting it fixed..

BTW, noticed in one of your ealier posts you mentioned "your gauges are reading fine".

FYI, there are two coolant temperatature sensors. One for the analog gauge in the dash, the other one for the ECM/PCM and the digital gauge display.

So, I presume it was your analog gauge that was reading fine, albeit the digital gauge was reading 'low' all the time.

 

yes, you are correct.....So simple to diagose now that it is over.......I hate chasing ghosts......my vette is back to being 100%.......from what I have read over the last two years...it will change.....but right now all is well in the world.....can not wait to get her painted and back together.......I miss driving her......