My car has thrown code 14 indicating that the coolant temperature sensor reading is too high. As far as I know, this means that the sensor thinks the coolant is at an outragous and impossible temperature (260F or higher?) I know this is not the case, because both fans work properly, thermostat works, coolant is full, in-dash thermometer indicates well under the 220F mark, etc. I think I would know if the coolant was really at that high of a temp. It has thrown the code a few times. I replaced the sensor itself, and still got the code 14 once in a while. I then replaced the wiring harness to the coolant sensor, and still the computer would throw me code 14. Well I didn't know where to go from there, so I gave up on it for a while. I finally got access to a scanner and was able to read exactly what temperature the CTS thinks the coolant is at. Here are a couple results:

Completely cool engine (sat for a full day), the air temperature outside was about 17C/62F--Scanner indicated that the CTS was measuring the coolant temperature to be 32C/90F, quite a lot higher than the outside temp.

Engine ran in park for a few minutes up to normal operating temperature. In dash gauge indicated a few notches below the dreaded 220F mark. I would guess the coolant was somewhere around 170F to 180F. The CTS, according to the scanner, said the temperature was 120C/248F.

So I think the two above tests confirms that the CTS is not reading the the coolant temperature correctly and is in fact sending false (high) readings to the computer. How much would this screw with the computer? Do these false temperature readings significantly alter the amount of fuel the computer thinks the engine needs? I am having problems passing smog, the car runs a little rough, and I experience surging when driving at partial throttle as if I was tapping lightly on and off the gas about 2 times per second. So I was wondering if anyone could give me any insight into getting rid of the code 14 and whether or not this may be responsible or partly responsible for it not passing smog and the surging. Any insight or comments would be appreciated. I know this was long. Thank you for taking the time to read this.

 

Assuming the new CTS you bought is good.
First, have the battery checked. Check the 5volt reference on a car that is running properly. Maybe some of our members can post there ECM 5volt reference.
Second, check your ECM 5volt reference (pin C14) to the 5volt return (pin D2) at the ECM 32 pin C-D connector is within specifications, if it is then check your sensor wiring, and connectors for clean tight connections, do the same for the ECM connectors.
Fnally, if the 5volts isn't up to specs then, while monitoring the 5volts disconnect the sensors that use the 5volt reference i.e TPS, MAT one at a time. if the 5volts returns to spec that sensor, or it's wiring/connector may be faulty. If all the 5volt referenced sensors have been disconnected and the 5volts is still out of spec the ECM may be faulty.

 

Well it's been a while on this one, but I still have a problem with the cts and code 14. The connection at the ECM looks fine. Continuity is fine. I got 5 volts at the cts connector. The reistance at the cts seemed ok, although I only was able to check it at one known temperature, ~90F, which is approx. the temp. outside. At that temp, the Ohms read 1.7k. According to that chart posted by Vader a while back, that is approximately correct.

Another thing: When I had the scanner hooked up, and the cts disconnected, the computer still showed ct reading of about 60 or 70F. Is that normal?

Is it possible that I may have a ground issue or something? How would I go about checking that out? Other than that, maybe my ECM took a nosedive....

--AA

 

This should be correct for almost all GM temperature sensors:



By your feedback, it seems that the sensor itself is functioning correctly. I would suspect that you have some other problem in the wire harness that is presenting resistance to the ECM input. Since you scanned the ECM and it reported 60-70°F with no sensor connected, it would appear that there is about a 4,000-5,000 ohm resistance in the circuit without a sensor connected. That could be due to contamination at a connector, including the CTS connector itself, the ECM harness connector, or contamination on the ECM mainboard itself. Solder flux, atmospheric dirt, and humidity can create conductive deposits on circuit boards and in connectors. Don't be so quick to condemn the ECM hardware itself.

A relatively easy and safe means to test this theory is to get a 10K resistor (or thereabout), measure the exact resistance with your ohmmeter on a 20K scale, then plug it into the harness in place of the CTS. Measure the resistance across the resistor again on a 20K scale so that the current of the meter does not damage the high impedance ECM input. If I am correct in my calculations, you will measure something more like 2,000 ohms, and not the 10K ohms that you plugged into the connector. That would indicate a wire harness, connector, or ECM mainboard problem.

Repairing the contaminated connectors may be a matter of only cleaning and drying them. Repairing the ECM may be the same thing, although the cleaning process would be slightly different.

To clean the ECM mainboard, disconnect the battery cable to power the system down. Remove and unplug the ECM. Remove the ECM case halves, then remove the CALPAK from its socket. You can then wash contaminated areas of the ECM board(s) with hot, soapy water and a stiff brush, rinse with hot, clean water, and allow it to dry thoroughly before reassembling the ECM. Do not use compressed air to force dry a circuit card - EVER! You can force water into places it shouldn't go, and create static electricity that can damage components. Just be patient and allow it to dry. I frequently "cheat" by placing a washed card under an incandescent lamp to slightly heat it and speed the drying. Just monitor the card to make sure it gets no warmer than you can handle comfortably.

As long as they are thoroughly dried, most circuit boards are water washable. Very few electronic devices made in the last 30 years use paper capacitors any more, so the components themselves are impervious to water so long as you don't use compressed air to dry them. I've done this hundreds of times in numerous applications, and frequently get "that look" from those who are uninitiated. Common sense dicates that electricity and water don't mix, but water washing 800V servo drive cards and EDM and RF power supply boards has never bit me in the backside yet. For those that have doubts, coinsider the fact that most large RF amplifiers (like radio and TV transmitters) use vacuum tubes for power output that are cooled by water (yes, they still use tubes), and the water is exposed to live electrical busses and parts at voltages much higher than most of us would ever encounter.

 

Thank you guys for the insiteful posts. Very helpful. I will definitely try that stuff out.

Before I read Vader's reply, I was doing some testing as suggested by Vader back in 2001! I hope that old information still holds up! Anyway, I backprobed the connection at the ECM, turned the key on and got a voltage of approx. 4.1V, which is quite a bit higher than the expected 1.98V (Engine was "cold", approx. 90-100F). After I warmed the engine up just a little, the Voltage at the ECM began to go down and was steadily decreasing until I turned off the car. I assume that it goes all the way down to ~0.04 volts or so before it throws the code 14 at me.

I hadn't checked the black ground wire for continuity, so I did that and it check out ok.

Stay tuned for more updates.

 

Well I haven't tried cleaning the ECM mainboard yet. Just out of curiosity, I ran the engine until it threw the code 14 at me, and then checked the voltage at the ECM by backprobing the connector. The voltage was about 1.8V. I'm having trouble making sense of all this. The code should be thrown when the voltage drops below 0.01V I thought.

It makes sense to me what Vader said about there being 4k to 5k ohms of resistance somewhere in the system with no sensor connected. It also makes sense (I think ) that since there is extra resistance somewhere, that the voltage that the ECM is seeing would be higher than normal at any given temperature.

What I don't get is why is the computer throwing the code if the voltage appears to be between 4.1V and 1.8V? Somehow, the computer interpretted the temp. to be somewhere around 275F (or whatever temp. it throws the code) with a corresponding voltage at the ECM of 1.8V. It seems like code 14 would result from the computer seeing not enough resistance, which would result in a very low voltage, which would be interpretted as a very high temperature.

Maybe I'm off base here. Electronics is definitely not my specialty.

Any comments, questions, suggestions, insight, or corrections--please feel free. Otherwise, I'll just keep on talking to myself.

 

I'll back up what Vader said with my own experience..... if you unplug the sensor the ECM should be showing -40*F (cold as it will go, infinite resistance basically).

If it's not the wiring harness or sensor I would begin to wonder about the possiblity of a bad ECM. Internal grounds/contacts/electronics simply going bad and not interpreting the signal coming back from the sensor correctly.

A junkyard ECM for $20 can be a valuable diagnostic tool!

I'd also disconnect the harness from the ECM and directly probe the 2 terminals that go to the CTS with an Ohmmeter. If it's showing resistance like in the chart Vader posted then you know the sensor and woring harness are doing their job and there's really not much left but a bad ECM.

 

Yeah. I hadn't thought of checking the resistance at the ECM harness. I checked the resistance throught cts harness and that matched to the resistance measured from the cts itself. Now, if the resistance at the ECM harness is the same as the resistance measured at the other two locations (or at least very close), then that would indicate the wires are all fine, and the computer is bad. And if the resistance is different (I would be expecting it to be higher, I think), that would mean there is resistance somewhere in the wires between the cts harness and the ecm harness, and therefore the computer is most likely fine. I'm trying that first thing tomorrow.

This problem WILL get solved yet!!

--AA

 

hey AA89GTA I'd agree with what Vader said, and you might want to look into a new ecm if you can't clean up your current one. More than 10 years of weathering and corrosion, and you have a good chance of having something being misread, misunderstood, or not being able to function properly translating into something else not functioning correct, and so on. But it's obvious that the computer is being mislead b/c if your car was running 275+, you're nice AFR heads would be done for, but they're fine!
just my .02.

 

Well, I finally have an update for anyone who cares. Hopefully this information will help someone in the future. I had taken resistance readings, both at the CTS and where the wires connect to the ECM. I checked and compared the readings at a few different temperatures. In all cases, the resistances were very close to eachother. That told me that the extra resistance I was somehow seeing (according to Vader, above) was not in the wires, and must have something to do with the computer itself.

So, I finally bought a remanufactured computer, and hooked it up. Ran the car up to the temp. where it normally threw the code 14...and...no code. I've driven it for about a week now, and I still haven't gotten that code 14 to come back up.

The car idles steady now at about 600rpm in drive. I probably need hook it up to a scanner to readjust the minimum air and then the tps to get it to idle a little bit higher and see what precise rpm it is idling at. I also still need to hook it up to a scanner and see what temperature the computer is getting from the CTS now, just to make sure the problem is really solved.

Well, that's all for now. I hope the problem is fixed for good. Should be one more update to confirm this. Thanks to all who have posted to help, and I hope this thread can be of some help to someone in the future.

--AAron