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Discussion Starter · #1 ·
a few weeks a ago my blazer (01 xtreme) started running like crap. the temp gauge would drop all the way down like it wasnt reading and the the truck would rev up and/or stall out. then the gauge would start to read normally again and it would run just fine. after a few days of doing this the check engine light came on with the code P0118 coolant temp sensor circuit high input. yesterday i changed the sensor, now the it runs just fine but the check engine light is on and the temp gauge dont work. i inspected the pig tail when i swapped the sensor, its not corroded or have any wires exposed on it. any ideas on what could cause this?
 

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Dash guage sensor and the CTS are different sensors on most trucks... Newer ones like yours may use the PCM to drive the cluster, and you may have a bad PCM..... Check your grounds and battery connections good.
 

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i saw what you did there!
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yeah the dash guage temp sensor is in the driver side cylinder head

has nothing to do with the ECM or the sensor on top of the engine with two wires that you are concerned with

this is the CTS

and it is for the ECM and helps tell the ECm what temp the engine is at and ho muvh fuel to inject

as so does the TPS and MAP sensor and so forth

alot of combined inputs from different points of the engine help control fuel injection

the CTS is just one of them


if the connector or wires to it are in poor condition then go to parts store and buy a new pigtail connector for it
most stores have them for cheap now
 

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it has a new 180 degree thermostat and sensor, im pretty sure its a wiring issue
According to attached schematic for 2001 4.3 there's one cooling sensor which provides data to the PCM.

The PCM uses the data for engine management and also routes to instrument panel (IPC) on class II data bus for use with temperature gauge.

Its sort of scary if the only gauge not working is temp as this could indicate a problem in IPC.

I have a ScanGauge tool permanently connected to my OBDII diagnostics port which provides cooling temp readout. Perhaps you could check around as many of better scan tools can read most PCM operating parameters (coolant, intake air temp, MAP, etc).

If the tool plugged into OBD reads coolant temp - it'll indicate the sensor and PCM are doing the job but there's probably something wrong in the IPC (loose connection, bad gauge, etc).
 

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Urban Hick
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Yeah...later trucks only have one sensor. If your truck is running fine now, I bet it's the guage itself.....My guage used to get "stuck" at like 1/4 of the way...I'd tap on the plastic cover and it would jump to the correct temperature.....Till i eventually broke the plastic cover.....When I took the cluster out to replace the cover I blew some air around the temp guage needle. Guess it was just dirt in it....cuz its been fine since (1 year +)

Doesn't really explain the engine light still being on though :S
 

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Discussion Starter · #8 ·
its not running fine right now tho. a few days back it wouldn't start and still wont. i put a pressure gauge on on the fuel line and im getting 0 psi and you cannot hear the fuel pump kick on. if the CTS was responsible for this would the ECM stop the fuel pump from turning on or would the or would the system still pressurize and the injectors not fire?

also i never had the CTS code until i did the plugs and wires on it, i think the guy that helped me pulled on the pig tail not looking and mistaken it for a plug wire. the wires dont look warn at all
 

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The PCM primes the fuel system via the fuel pump relay. If the relay is bad, the wires to the pump, the pump, the ground for the pump, or the PCM, or the fuse for the pump, etc.
 

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Discussion Starter · #10 ·
ok at least im on the right track. i already checked all the fuses and relays and they are all good. to check a and see if im gettin power to the pump am i gonna have to drop the tank?
 

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Should be a wire harness you can get at......
 
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