I've just fixed my Check Engine light and it's giving me code 15, open coolant sensor circuit.

I get 5V from the lead that plugs into the top of the sensor with the key on but the engine not running. How can I test to see if the sensor really is busted or not?

My factory manual says that a yellow and black lead joins to the sensor - the black looking lead in the centre of the picture below really is yellow, it's just covered with black heat shrink tubing. I don't see a black wire at all.

Also on the thermostat housing but just behind the coolant sensor is another plug of some sort. But as you can see it's been broken clean off - anyone know what this might be for?

Now, let's see if I can attach a picture...

 

Code 15 means there is an incredibly low, pretty much impossible reading from the CTS to the ECM. This is usually blamed on either a bad connection or a failed sensor.

You can check the resistance against a known running temperature using this chart Vader has posted before:


Since you checked the voltage and that turned out ok, I would do the resistance test on the CTS.

Oh yea, the broken one is probably the EFE TVS or the early fuel evaporation thermal vacuum switch. It works in cooperation with the exhaust crossover. It sends vacuum when the engine is under normal operating temperatures. When it diverts the vacuum, it diverts it to the EFE valve in the right side manifold. The default position for this is 'open' allowing exhaust gas to flow as normal. When vacuum is applied, or when the engine is below normal op. temps, the valve shuts and diverts the gas up through the intake warming it, further promoting fuel evaporation.

 

Thanks for that explanation on the broken switch/sensor, that system has been removed from the car altogether I believe.

At what place on the CTS do I take a resistance reading from? Presumably the centre terminal of the sensor (where the yellow lead connects to), and ground? If so, I'm getting open circuit on my DMM when the car is hot or cold.

Where is the second wire of the CTS supposed to connect? I don't get how come I've only got one wire on my CTS.

 

The cts should be a two wire sensor. I suspect that your sensor is actually a switch. Try getting the car up to temp and then check the resistance. If it goes to almost 0 resistance you have a switch.

 

But how do I check the resistance? At what place on the sensor/switch do I take a reading? The centre terminal and ground? If that's the place I'm meant to do it, I keep getting open circuit which presumably means a faulty sensor/switch.

Does anyone have a picture of a two wire sensor with the plug so I can compare it with mine?

 

The "early" (through 1985 or so) CTS was one wire and is harder to find. How is the continuity of the wiring from the sensor to the ECM? I replied to your email about this.

 

Got your email thanks.

I presume because I get 5V appearing at the wire when the key is on that the continuity is OK. Maybe I should check this another way?

 

Usually the computer sends the voltage out and the sensor will vary the grounding to change the voltage according to the measurement. You should have a lower voltage than 5 at the sensor. Either a bad ground at sensor, take it out and clean the threads and reinstall, or a bad sensor which is more likely.

 

hmm, now I'm not so sure about it being one-wire. I haven't looked at my 83 in a long long time, and I don't have any spare parts to reference. But expect an email back tuesday.

 

I'll pull it out and see if I can clean the sensor threads. It's probably corroded or something, but yeah, as you say tom3, it's probably a bad sensor.

I have an idea that I'm going to try. First I'll clear the ECM of the code. Then, I'll stick a 350ohm resistor between ground and the 5V lead that goes to the sensor (when the car is warm). The resistance substitution should tell the ECM that it's warm and hopefully it shouldn't set a code.

I'll let you all know what happens...

 

Has anyone taken a good look Kiwi friends photo?
The carb is computer controlled, but has no t.p.s., only a mixture solenoid. The temp sensor doesn't look right for 1982 or 1983. Should be two wires, as he has said. But the wires should not join, I believe.
We should wonder how different his car is from a North American model. Also, his engine is obviously altered from stock. Do I make any sense, or have I had too much Corona beer?

 

Maybe an old Nissan/Datsun?

But then I'm drunk too...



~C

 

The carbs like you described were used in trucks through the 1980s. They do rely on temperature as an input in those systems. I've seen a few; never bothered with them however.

In his picture, I am seeing the female section of a TPS connector plug, I'm 99.44% sure; hidden by the heater hose. If he wishes to post the carburetor service # and further pics, I'm certain we can verify.

The temp sender in the earlier 1980s models is indeed different than one that was bone stock in a 1987 LG4 model, I am certain. Once upon a time, the 1982 T/A engine I had to "borrow" a thermostat housing from when I was at a friends shoppe doing an intake manifold reseal had a sender different than the 1987 sender. I am fuzzy on the one-wire / two-wire thing though. And I'm not sure the entire plastic "shell" of the pigtail is intact on his car.

I was thinking that NZ didn't get any 1982 f-bodies at all, and that his car had to be a RH drive conversion but again I could be wrong. I'm sure he will fill us in. As far as modified from stock; the evaporative emissions system shouldn't be an issue in this hurdle.

my .02USD,
-Matthew

 

I think I've got it!

While I was taking more pics of my engine bay I had a good look inside the CTS where the lead plugs in. Low and behold, the inside of the connector has a metal wall, and also the pin the centre (as I've always known). I took a resistance reading between these two and got a reading. The hotter the engine, the lower the resistance.

I then noticed a wire that had been lying around my engine compartment for donkeys years and I thought to myself "hmmm, I wonder if this goes in here", and it did.

It's not obvious at all, but there's a wire (which connects to ground), that has a cylinderical ring connector on it. This goes snuggly into the top of the CTS, and the yellow plug in the top picture then plugs into that. And there we have two wires going into the CTS. I reset the ECM, went for a drive and the check engine light never came on. I then checked for codes and the ECM seemed happy - wohoo!

I guess that's that problem solved. Thanks everyone! However, do I have the factory sensor at all? If not, would it be worth getting a factory style sensor? Do all sensors have the same resistance scale? And, why doesn't the ECM use the temperate sensor that connects to the gauges?

My carb does indeed have a TPS sensor, and you're right Matt, it's hidden under a heater hose in the picture. On my dashboard I have a TPS display module that I made which illuminates an LED per 10% throttle. It's quite groovy watching all 10 LEDs light up at night when you stomp on the gas.

My car was originally left hand drive, but in Australia it was converted to right hand drive. I imported it 2 and a half years ago and since then have done a LOT to the car.

You can drive left hand drive cars in NZ, most American cars here are. However if you import a car less than 20 years old and you haven't lived in the country of origin for at least three months then you must right hand drive the car. It'd be cheaper to live in the USA for 3 months than have the car converted.

In Australia it's different. If you want to drive an American car on the roads you must have it converted.

 

Sure sounds like an interesting car! Really has some history.