Jpr5690 sent me this to post (not sure who it's originally from).

Temp Gauge Mod

1. Take a 200 ohm resistor and unplug the temp sensor, and hook the resistor to terminals 'A' and 'B' of the plug. Turn the ignition on and read the temp gauge, it should read about 210° F. (maybe a little over, but memorize where the needle is)

2. Get a temp sensor from a 98 F-body

3. Get a temp sensor terminal plug from a 98 F-body

4. Hook a 20 Gage wire to terminal 'C' of the new sensor plug. (Terminal 'A' is sensor ground, and 'B' is sensor signal to PCM.)

5. Pull the two wires from terminals 'A' and 'B' from the old sensor plug, and replace them into terminals 'A' and 'B' of the new sensor plug. (Wires go from terminal 'A' to 'A', and 'B' to 'B')

6. Place new temp sensor into the engine head.

7. Pull the Gauge cluster out.

8. Run the other end of the new wire from terminal 'C' through the fire wall and into the cab, run the wire behind the dash and into a hole behind where the gauge cluster goes, and put an insulated female connector plug on the wire.

9. Cut another length of wire and put an insulated male plug on one end, and the other end gets soldered to the gauge cluster circuit board.

10. Take out the two torx screws that hold the back cover on, and pull the back cover off.

11. Take out the one torx scre by the plug pack terminals that's holding the circuit board on. Very carefully pull the circuit board off. (You need to go around the edges and gently pull up with your fingers while unsnapping the tabs.)

12. Take a razor and on the back of the circuit board (the pic shows where), make a cut next to the jumper solder joint on the printed circuit layout, and make another cut about 1/8 of an inch down from the first cut on the printed circuit layout so that a 1/8 inch piece of the printed circuit layout can be pulled off.

13. De-solder the jumper, and replace it with a resistor that will calibrate the temp gauge. (We will figure out the resistor's value next.)

14. Take the end of the wire that is to be soldered, and solder it into the solder joint that you cut the piece of layout out and pulled the jumper out.

15. Take a 5K.Ohm rheostat and hook it between the new wires coming from the dash and the gauge cluster, with the 200 ohms resistor hooked into terminals 'A' and 'C' of the sensor plug. Turn the ignition on, and turn the rheostat till the gauge reads what it did the first time you read the gauge with the 200 ohm resistor in the sensor plug.

16. Read the resistance of the rheostat, and that is the value of resistor to solder in the place of the jumper you took out earlier.

17. Put everything back together and test.

18. AutoTap or some type of scan tool would verify the accuracy of the temperature gauge after the mod.

 

thats alot of damned work..i think ill use my laptop if im worried about temp

but thanks anyway, im sure this will come in handy for some people.

 

nice write up

 

if someone does this PLEASE TELL US THE RESISTOR VALUE needed for the resistor that needs to be added to the cluster .. if we ll new this then it would elminate STEPS 14-18

 

also the PART NUMBER for the 3 prong temp sensor that would fit an ls1 block is 12551708 (as reported in the previous thread)

ALSO A PART NUMBER ON THE HARNESS PLUG NEEDED TO PLUG INTO THIS NEW SENSOR WOULD BE NICE BEING YOU CANT USE YOUR STOCK 2 PRONG PLUG ANYMORE

 

somebody fill me in here, what exactly does this do?

 

it allows the stock coolant gauge in 99+fbods to read an accurate temp instead of just reading 210 deg all the time

 

You see, mine tricked me into thinking it actually worked. It would read around 210 and then it dropped to around ~195 with my 160 stat and hypertech to turn fans on. Hooked up HPTuners to it and the damn thing was actually around ~225 degrees That's more than just a bit off.

 

THATS WEIRD BUT THIS SHOULD DO THE TRICK ive just been too busy to do this but im planning this mod sometime soon

 

I just found this and added it to the General Maintenance FAQ.

Thanks ACW & Jpr5690.

 

Woohoo! I Actually Made A Sticky!

 

i was actually thinking about this last week. i knew it wouldnt take much to actually make the gauge work.

not to critique your method, but that must look kinda janky. im the kinda person that likes making things look factory. and to do this right i'd find an empty cavity of the factory connector and make it work that way.


actually no i'd run the wire from the sensor along the factory harness to the pcm and then find which wire leads from the pcm to the cluster that carries the temp gauge feed and just run it to that.

wait is the cluster bussed from the pcm? then it wont work if it is...

 

great writeup man. i hav a live data scanner so i can just get the readings off that

 

I would wonder about the possibility of installing the temp sensor in the other head and leaving the factory one in place. Then run the gauge of this newly installed sensor

 

it does not read 210 all the time, the gauge just doesn't read linearly through that range. I've run a scan gauge reporting temperature and at 210 F the needle is straight up on 210. From about 185-200 if you look head on at the gauge you can see the needle slightly left of 210, and at 220+ the needle is slightly to the right of 210. Not until > 230F will the needle significantly go to the right of 210, per the service manual the radiator fans come on at low speed at 22x F and at high speed at 234F or 236F.

 

So your saying the new cars guage actaully works but its just not reading accuratly through normal operating range?

 

^^yes, all temp gauges on cars are like this now. To solve this issue I just installed an aftermarket gauge with another sending unit.

 

The newer gauges work like this.....fuel and temp gauges use a AVERAGE reading taken constantly. Ever wonder why your fuel gauge doesn't bounce all over? Because the computer is watching the AVERAGE reading the sending unit is sending to it as you are boucing up and down the road the gauge reads perfectly fine.

Same with the temp gauge....it reads a average and shows it to you SO you don't see the gauge spiking high or low as the Tstat open etc BUT you are seeing a correct reading of the average temp of the engine. If it starts getting hooter the temp gauge will go up, same if it runs cooler.

People complained about the temp gauges spiking up and down so GM just went to the way the fuel gauge works.

 

Did you just make up that whole averaging thing? Thats just take your meds.

 

Dont be an azz...how the hell do you think it works! The fuel gauge would be swinging all over the place.