Please Help! Cant find source of OBD1 Code 15 Coolant Sensor Error - What Next?
 

1995 S10 Blazer - Vin W -
Keeps stalling out seconds after starting.
Getting OBD1 Code #15 - Coolant Temperature Sensor Error.


Just finished rebuilding the 4.3 Vortec Engine so most parts are new and clean. Engine ran fine during the initial breakin period (60 minutes) for the rings, but now am getting code 15 and stalling.


When I changed the Coolant Sensor itself, and checked the computer for the error code BEFORE attempting to start, the code was not there. After attempting to start, car starts, idles well for about 15 seconds then stalls. Then the error code 15 returns if checked.


Already:
Changed temperature sensor itself twice - correct one with two wires
Changed Pigtail & 18" of wiring harness - Soldered connection well.
Swapped out PCM computer with a second hand computer from same model car in case it was the PCM - Still getting same error.


I am not sure where to go next. I checked the PCM, the two wires, pigtail and sensor. Still getting same code 15.


The only thing I did not do was take apart the entire wiring harness and change out the sensor wires all the way back thru the firewall to the computer itself inside the dashboard.


I NEED HELP AND ADVICE NOW:)


Thanks All,
Nick

Can anyone help? Still looking for a solution here.


UPDATE TODAY: Still attempting to get rid of the Coolant Sensor Error 15, rough idle and stalling.


I noticed today that coolant sensor ground wire eventually joins to the TPS sensor ground wire. Although I am not getting ANY Throttle Position Sensor codes, I found if I disconnect the TPS sensor... then the stallilng at idle stops. The car will not stall easily, tho is still not idling smooth, and Im sure now with the TPS code since the sensor is unplugged.


SO MY QUESTION... could an error with the TPS or the TPS wire pigtail somehow set off a Coolant Temp Sensor OBD1 code?


I am changing the TPS and Pigtail tomorrow to see.


Any Ideas??




Nick

bump....


Still looking for help. Cant find cause of the Coolant Temp Sensor Code 15.


I changed the TPS sensor and pigtail and no difference. I even changed the Idle Air Control valve. No difference.


Still getting Coolant Sensor Error Code 15, sometimes Knock Sensor Error, and Car Idle Erratically and stalls without accelerator depressed.

Only thing I could think of is that the coolant temp sensor maaay be confusing the computer. I'm not sure if the resistance goes up or down on the blazer sensor (i presume down as the temp increases).
For example if it's saying that the engine is truly cold but the temp sensor is telling the computer that it's at opperating temperature it'll run leaner than a true cold start and could cause the idle to be off..

I haven't had personal experience but i'd be interested in testing the resistance of the sensor and the wires that go to the brain.

The conditions for a code 15 :

• the coolant temperature reported is < -29 deg F (-34 deg C), and
• the above condition is present for more than 4 seconds
  
  This leads me to further believe a resistance issue in the sensor itself or the wiring to it.
  
  A reading if the true coolant temp is at 70 degrees Fahrenheit should be about 3400 ohms

Hmmmm

My 2 cents worth of suggestions:

1st) There are 2 sensors if my memory doesn't let me down.
2nd) Coolant level or air bubble around the sensor?

Troubleshooting: Dump the sensor (or another sensor) into a cup of hot water?

Have you checked the Purge TVS valve? It monitors coolant temp and regulates vacuum. Also I would get a vacuum tester for testing to identify possible idle problems