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#1
06-22-2005, 06:57 PM
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temp sensor
97 Mazda 626,New coolant temp sensor,fan will not turn off,A/C comp. will not turn on.On scanner before replacing sensor temp read 250.With new sensor it reads 330.Engine cold.Any ideas?
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#2
06-23-2005, 07:50 PM
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Re: temp sensor
Quote:
The first failure was the ECT sensor went bad and increased in resistance. The book says at room temp the ECT should read 2.2Kohms to 2.5kohms. This sensor went to 3kohms which makes the PCM think the engine is really cold... When the engine is cold, you don't need the fans running..... Well I'm driving around in 90deg Houston weather with the Air-con on.... I kept overheating... It took me a few overheats to find the bad sensor... When I overheated, I noticed the fans were dead... I drove it home and tried to troubleshoot why the fans weren't coming on... I noticed if I turned the Air-con on MAX A/C both fans would come on.... So, that told me the fans worked.... I checked the relays and swapped some and nothing changed, so that tells me the relays were good... By swapping a relay out with the same relay, if that relay was bad, my problem would change with the relay change... but it didn't... Finally I got around to checking the ECT... It read too high..... That means the PCM thought the engine was still cool and didn't need the fans runing.... Wrong! Bad sensor!!! I bought a new ECT and popped it in... The new one reads 1.8kohms at room temp which is Too low... I took it back to the autoparts store and got another... The new one read 2kohms... Still too low but I didn't think another one would be any better.... Now my problem is the PCM thinks the engine is too hot... It runs both fans and won't let the Air-con turn on.... For now that isn't a problem in this Texas heat... I don't mind both fans runing constantly on the engine... I DO mind not having any A/C.... I'm HOT... I found a potentiometer in my junk box... I turned it to read 3kohms. I stuck it in the conector for the ECT.... Turned the ignition on and everything works great... The fans stay off while the engine is cool, the A/C comes on and cools... But that leaves the engine without any temp feedback to the PCM... I'm thinking about adding a resistor in line with the too-low-ECT to make it read closer to 2.2Kohms at room temp... Fine tune it... When the engine gets hot the ECT will still lower it's ohms reading the hotter it gets... The theory is valid... Or, is the PCM smart enough to calibrate the difference out after driving it for a few miles? As for now I'll live with a cool engine and a hot interior while using the autoparts ECT that reads too low...
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#3
06-23-2005, 08:50 PM
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Re: Re: temp sensor
Oh, my point was that I think we are getting some bad ECT sensors. Your sensor thinks the engine is warmer than it really is, my sensor is the same... That's why the A/C won't come on...
I'll try to find an OEM ECT from the dealer and measure it's resistance. In the dealers nice airconditioned office that ECT should read over 2.5kohms with an ohmeter. I won't buy it if it reads any lower. Of course, something else might be wrong with our cars... Maybe the PCM needs to be reset by the dealer after changing the sensor....??? alancl1
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#5
07-08-2005, 02:46 PM
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Re: Re: Re: temp sensor
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at advance auto parts were GP Sorenson and they all read 1.8.Holding my hand around it the resistance dropped rapidly ,with engine heat i`m sure it would have no resistance.
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