Slayer

To preface my problem, after the top half of my engine was rebuilt a couple years ago, my chip was re-tuned. As part of the re-tune, the fans were programmed to run all the time, keeping my temperature at 140 degrees.

Last week, I noticed my temperature gauge fluctuating. I checked the radiator, and it was a bit low, so I topped it off. I also replaced the radiator cap just to be safe because I still had the stock cap from 1993. Later that night, the temperature gauge started to rise again, and by the time I got the car to my work parking lot, the temperature gauge was at 260 degrees. I figured I better swap the thermostat. The next morning, I was able to drive the car home, but the temperature was still rising.

It turns out the fans won't run when the car is running. When I run the A/C with the car running, the fans turn on, but they shut off when I shut off the A/C. When I "jump" the OBD connector with a paperclip, the fans turn on. (No codes, by the way.) When I disconnect the coolant temperature sensor, the fans turn on. I replaced the coolant temperature sensor this morning, thinking it was the culprit, but the same things are happening with the fans. The fuses and relays are fine, and I even disconnected the battery to reset the computer, hoping that would help.

Has anyone else had a similar issue? I'd like to be able to drive my car more than three miles at a time because I can't get very far driving it like that. I'm thinking I may just keep the coolant temperature sensor disconnected, but I'm not sure if that would cause any problems.

Injuneer

You running a t'stat? Wouldn't seem compatible with the extremely low running temp. Not sure why you would want it to run that cool.

Or, maybe you are just confused by the mismarking in the 93 coolant temp gauge. Although the bottom line is marked 100*F, suggesting that the 1/4 line is ~160*F, that is not what it is really indicating. The correct number for the bottom line is 160*F, and that was corrected on the later year gauges.

http://shbox.com/1/temp_gauges1.jpg

If you disconnected the coolant temp sensor, or if it was bad, you would have set a code (DTC 14/DTC 15). You need to check the wiring for the temp sensor at the water pump:

Again, courtesy of Shoebox

4th Gen LT1 F-body Tech Articles

Slayer

Thanks for the information. I never knew that about the temperature gauge. My gauge never used to climb above the 1/4 mark, which would be approximately 180 degrees.

When I disconnected the coolant temperature sensor and started the car, the fans did turn on, but the SES light did turn on.

I'll check the wiring, as you suggested, because that's the only thing I haven't tried yet.

Injuneer

There is obviously no problem between the ECM and the fan relays. The only thing I can think of is a problem in the wires to the CLT sensor. Check for 5V with the key on, as Shoebox recommends.

Another remote possibility - the CLT sensor in the water pump shares an ECM sourced ground with the TPS sensor. Make sure there is no problem with the TPS.

shoebox

Observation of temps and fan status with a live data scan would be my suggestion.

GaryDoug

Is the pcm a 93? When you grounded pin B (A to B), did the SES lamp flash code 12? I wasn't aware that the 93 had a field service mode that would turn on the fans.

Slayer

Yes, the PCM is a '93, but the chip has been reprogrammed after I had all the engine work done a couple years ago. When I "jumped" the OBD connector with a paperclip, code 12 is all that flashed.

I think the coolant temperature sensor connector is bad. I followed Shoebox's directions. When I tested the connector, I got a reading of 5 VDC. When I tested just the power lead on the connector, I got a reading of 5 VDC. However, when I tested the ground lead, I got a reading of 1,085 ohms. According to Shoebox, I should have gotten a reading close to 0. A very high ohm reading indicates the lead is open.

So, it should be fun trying to splice in a new connector. Looks like I'm going back under the car tomorrow.

shoebox

Gary, IIRC, the fans have always come on when you short the pins to flash codes, even on earlier GM PCMs.

Slayer

I spliced in a new coolant temperature sensor connector this morning, and I tested it before starting the car. All the voltage and ohm readings were normal; however, the fans still won't turn on. I'm letting the car cool down, and I'm going to put the old thermostat back in because I don't think it was bad to begin with, and the spring-loaded base of the new thermostat I installed is much shorter than the base of the thermostat that was originally in the car. If that still doesn't work, then I'm out of ideas.

Injuneer

You probably installed the incorrect t'stat - common problem:

Courtesy of Shoebox

http://shbox.com/1/tstat.jpg

Do you still have 1,000+ ohms on the ground side?

Slayer

Yeah, I was worried about the new thermostat being an SBC thermostat, but it actually was the same length as the old thermostat. I tested the old thermostat before re-installing it, and it opened just fine. I just put it in the car, and the fans still won't turn on. I guess I'll ask my mechanic to bring his Snap-On scanner to the house to monitor the computer when the car is running. I don't know what else to do now, except just drive with the coolant temperature sensor disconnected, but the car seemed harder to start with the sensor disconnected.

No, the ground side of the new connector is reading 1 ohm now.

Injuneer

You can scan it yourself, and run a detailed data log of the ECM, using Scan9495. I can help interpret the data. Building or buying a cable will probably cost less than the dealer will charge you for a 1-time hookup.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Slayer

My mechanic won't charge me becasue he's my neighbor, so he said he'll bring his scanner to my house the next day I'm off work this week. Hopefully, his scanner sheds some light on this issue.

Injuneer

While observing the CLT sensor reading on the Tech-2, compare it to what the dash gauge is indicating, so see if they agree, recognizing that the gauge is fed by a different sensor.

Slayer

I thought I had fixed the problem yesterday because I realized that I had forgotten to bleed the coolant system as I was filling it. I bled the system yesterday, letting some air escape; however, the fans still wouldn't turn on. This morning, I decided to test the sensor and connector again. The sensor tests fine, but the connector is once again showing almost 1,100 ohms on the ground side. When I first installed it, it tested fine on the ground side.

So, my question is, Did I possibly short out the ground side of the coolant temperature sensor connector by running the car hotter than normal (up to 235 degrees) without properly bleeding the cooling system?