Temperature Senders

[safety_match]

Does anyone know if my 1990 has TWO temperature senders? I'm having some trouble with overheating and I'm told that my 1990 may have one 12 volt sender to power the temp gauge and another lower voltage sender to supply the ECM.
Both cooling fans are inoperative (although they are fine when power is put to them), I have changed the relays but still no go. My temp gauge works OK. I now wonder about a second sender or the ECM itself.
Any thoughts?

thanks,
safety

 

[pns0ccc]

Not sure about two sensors on 1990, On my 96 the Cooling Fan Temp switch/sensor is located on right side of cylinder head right behind engine oil dipstick, the Coolant temp sensor is mounted on water-pump. Have you tried turning on A/C to see if both Fans turn on automatically. Also you may want to take an external engine temperature reading to verify your indication is correct.
I believe the ECM starts the Primary cooling fan when coolant temp reaches 226 degrees F, when A/C is on of if coolant sensor or coolant diagnostic code is happening. ECM will command second fan on when (primary fan already on) engine temperature exceeds 235, A/C is on or if coolant system problem is has occurred.

 

[SPANISHVETTS]

Yes U have 2.
The digital one is under the intake by the thermostat. the analogue one is on the right rear side of the motor just above the exhaust.
Check the digital connector. These guys get dirty and cause problems.
What is the digital temp. reading? The analogue gauges are not accurate.

 

[safety_match]

thanks pns0ccc and spanishvetts

pns0ccc: Yes, I've turned on the AC and again nothing.

spanishvetts: I only have the analogue gauge. Being an analogue gauge it may not be completely accurate but when it went up to 250-260 degrees it was indeed hot!

I will check the senders next and if no luck there I will look at the ECM (being $305 CDN I will leave this last). I suppose the fusible link could be another trouble spot?

thanks

 

[c4cruiser]

1990 was the first year to have both analog and digital gauges. There should be a button labeled GAUGES on the dash that will cause different digital displays to appear right under the speedometer when pressed.

You should be able to toggle between volts, water temp and oil temp.

Turning on the A/C forces the fans to run constantly. If the fans are not turning on at all, you should suspect the fan relays. If the analog gauge did show a hot reading and the fans are not coming on, the problem is probably not with either of the temp sensors. In any event, relays are not too expensive (I keep a spare relay in the garage).

 

[pns0ccc]

When you test the Fusible link you should check the 3 amp fuse? Something else you can try is to use a short piece of wire to ground the ALCL terminals A(ground) to B(diagnostic). Turn the ignition on, with engine off, both of the fans should come on. If the fans do not operate go to the cooling fan relays and with the ignition keys on and engine off, ground the F terminal on the relay on the non working fan or fans. If the fan runs then the problem may be with the ECM. Before paying for a new ECM you may want to have the memory reflashed on the ECM by a Dealer. This has helped in some cases. Good luck.

 

[SPANISHVETTS]

I am in agreement with c4cruiser and pns0ccc, sounds like a wring or relay problem. ECM failures are few and far between. Most problems come from bad ground connections or dirty plugs.

Why not pull your ECM codes? You might have some interesting history. For help and more info go here http://www.c4vettes.com/indepth_launch.htm for the codes and here http://www.c4vettes.com/codes.htm for detailed info on recovery of the codes for a 90.

You can also get some good info from the HVAC system http://www.corvetteactioncenter.com/kb/question.php?qstId=142

 

[pns0ccc]

SPANISHVETTS has listed excellent links. The detailed information and graphics make your troubleshooting easier. Use caution when you start grounding any electrical device due to possible damage to your electronics if you make the wrong connection.
(SAFETY NOTE: WHILE TESTING FOR VOLTAGE WITH IGNITION ON REMEMBER THAT dc VOLTAGE WILL KNOCK YOU ON YOUR BUTT!)
After checking ECM codes do not be surprised if none are active. You can have a trouble or fault without a code in memory. I've seen this many times. The problem may be after the inputs to the ECM. I would start my test at the relays. You can start engine and turn on A/C and check for voltage at relay to see if signal is even coming from ECM to activate fans.

 

[maxm]

c4crusier...i have a -90 but i don´t have digital readings. I don´t have the button Gauges. Is there a differens in the same year ?
Max

 

[SPANISHVETTS]

If you have the export mod. (RPO EXP, etc.) or the dual mode, Miles and kilometers dash board the Gagues switch becomes the english/metric switch.
No prbolem to get the digital readouts, use the HVAC module and folow the instructions I posted above.
This might not be true for all modles, I have ben on the wrong side of the Atlatic for too long.

 

[maxm]

SPANISVETTS...pleas explain. I can not get digital reads. I´m i missing something.
Max

 

[safety_match]

maxm: I believe we both have the digitial and analogue dash. Our voltmeter, water temp, oil temp and oil pressure are analogue. The english/metric button only controls the speed/trip, range, mpg and inside/outside temperatures.

 

[safety_match]

Thanks everyone...I believe I have the overheating problem under control now. It was as simple as the fuse being blown. The confusing issue was that on my fusebox that fuse position is marked as "gauges".
We found the solution in the Owner's Manual. The Owner's Manual stated that fuse #9 controls AC, cooling fans, and DRL. But the fusebox labels it differently so we weren't looking to check the "gauges" fuse.
I replaced it with another 10A fuse and will watch it carefully to see if it blows again. There may be a reason why it blew in the first place.