I getting a code 15 ( Coolent sensor is too low) Is this a temp sensor or a fuild level? and where is this sensor on a 88 2.8?

 

It's a temp sensor problem. It''s a 2 wire sensor located in the intake manifold next to the thermostat housing.

Chances are that the CTS is internally shorted and needs to be replaced.

 

Thanks

 

Agg.. went and replaced the CTS and Im still getting a code 15..

 

Did you replace the CTS or the Sender for the guage, the sender has 1 wire, but the connector is similar and they look almost identical.

 

I did the CTS.. And I just reliezed I didnt clear the computer.. So I shall see tommory if it worked

 

Ok, Code 15 is Coolant Temp Low, not CTS Voltage low like I thought. You'll have to check out the wiring going back to the computer for opens and shorts to ground.

Here's how the whole thing works:

The CTS is a Negative Temperature Co-efficiant Thermistor, which means it's resistance value changes opposite it's temperature. The Higher the Temperature, the lower the sensors resistance.

The computer uses 2 wires to sense temperature, one of them is a Source voltage/Signal wire, while the other is a ground back to the computer. The ECM sends 5V down the signal wire and measures the voltage drop across the sensor using the returning ground wire. The Cooler the temp, the higher the resistance, the higher the voltage drop across the sensor and vice-versa.

So if you have an open or short to ground at any point in either wire, the computer is reading that there is a difference of 5V between the 2 wires, so it thinks it's -47*F out.

When it sees that engine temp is reported as -47*F but the IAT is saying it's higher than that out, it sets a code 15 because the coolant temp is being reported as "too low."

I have a diagram that I drew up of the circuit and how the ECM senses stuff if you would like a visual representation of the circuit. Just let me knwo and I'll post it.

 

I would like to see that diagram cause i took my car to the dealership and the mechanic said i had a broken ground to my CTS so he just patched it to a genaric ground in the wire harness. so could that account for my car not going into closed loop mode and the fan not turning on?

 

The Fan..no, there's a seperate sensor in the back of the right head that controlls the fan, but the closed loop thing...YES, most definiitly, since coolant temp is on of the major factors in determining when to go into closed loop.

The comparator in the picture is basically an internal volt-meter. It measures the voltage drop across the CTS, which is basically how much voltage it consumes from the circuit.

 

ok so i need to find that proper ground to get it to work again? also i get no codes other than the EGR one.