(07-12-2020, 01:16 AM)GeorgeGEO Wrote: Recent new owner of a 96 Geo tracker 16V 2door 4wd MT with 230k miles .

CEL is on for p0118 - Engine Coolant Temperature Circuit – High Input malfunction
Runs rough after warm up and dies at idle after warm up = rich condition 

Also temp gauge at dash starts when cold , at half warm mark and one warmed up shows full / pegged HOT .

Live data with hand held scanner plugged into OBDII port shows -40 for coolant temps at all times . ( it does not lie to you , wires cut to ECT or sensor is bad)

Replaced both the CTS (old name) ECT (new name) CTS is 1980s samuria days, for ECU and the temp sensor for dash = no change  but what did the new ECT OBD2 scans show?

Tested the instrument cluster by unplugging the temp sensor for dash indicator while running = no change ( still indicates wrong temps )

Tested the new CTS with OHM meter ( pig tail unplugged ) = tested good ( 2.7  no that is 2.7K or 2700 OHMS or something like that bone cold )
when using any DMM , look at the LCD,  with Greek omega symbol on LCD that is  pure homes, so 2.7 is 2.7 homes but With K icon on the LCD that  is x1000
k= 1000,for kilo.
M-  1 meg, range,  or x1,000,000 or x 1meg.

Tested the new CTS with OHM meter ( pig tail plugged in (this is invalid test)) = tested at 1.75 or something like that, bone cold ,  at backside of pigtail.
why skip measuring both old and new ETC, unplugged. ?

so with engine "FULLY" hot, you pull the ECT connector, and the 2 pins on the ECT read 300 ohms or 0.3K ohm.  this proves sensor, is reading 180f.
most times the thermostat is bad, they last 7 years, and fail. too hot or too cold, endless and forever true. the wax pellet inside short lived,
or worn thermostat, 160f is dead nuts wrong, and will cause the ECU to go nuts and show, wrong temp scanned
but your  scans show the wires to the ECT are cut in the engine bay or the dash.

this is 100% electrical problem ECU to ECT, wires bad. and there are 2 wires.


My Q is .......

I think, I have a problem with the actual instrument cluster and Im wondering if the wiring for the CTS is looped into the cluster some how ?
no  ! the gauge has its Very own sensor, in fact is 1 pin Faston™ type connector push on single pin.  

1. plug in the ECT first.(conn)
   
2. pull dome fuse for 1 min ,
   
3. put back dome fuse. DTC memory is now erased, no matter what.
   
4. key on
   
5. scan oBD2,again.
   
6. now it scan reads  right for sure engine running,
   
7. if you key off a hot engine the coolant will go over 180f, and SCANS tell you it did and is normal called hot soak temps.