Pontiac Repair: Grand prix coolent running cooler, digital volt meter, coolant temp

Question
QUESTION: Todd,
My 2004 Pontiac Grand Prix has a cooling issue.  A few months back the check engine light came on and needed a new Thermostat.  This was changed.  A few weeks later the light came back with a temperature sensor fault this was changed.  The light came back after approx two days.  The pig tail wire was changed.  The temperature sensor fault exists and the engine never get's higher than between 1/4 and 1/2 cooler than "normal".  Any idea's what to check next?

ANSWER: Hi Nigel:

what code is setting on this? the engine coolant temp sensor for the engine computer also if the feed for the gauge on the dash. So if there is an issue with the sensor the gauge will read wrong as well. the temp sensor is a very simple circut the compuyer sends out a siganl the resiatnce od the temp sensor changes with tempature and the volatge change across that sensor is what the computer sees abd adjusted the fule delivery and sends a signal out for the gauge. if you replaced the sensor and the harness make sure the senor is wired correctly and use only an AC delco sensor a fits all from the car parts store will not do. any fuel injetion parts should be replaced with the exact replacement from what ever manufacture your working on. good luck :-}


---------- FOLLOW-UP ----------

QUESTION: Thanks Todd, Before I go out and buy another sensor the one I purchased was not Delco the pigtail wire was black wires only.  I did notice the GM plug was black to white at the connection at the harness.  How can I tell if this is backwards?

Answer
on the connector it is labled a and b the yellow wire goes on the terminal marked a and the black wire goes on b.

Those are the colors of the wire on the engine side of the wire harness.
Hope that helps. you can also make sure that the powerr and groundto the sensor are good with the key on use a digital volt meter and check across the 2 wires it sould read close to 5 Volts.