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Guest Message by DevFuse

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'93 Legacy Code 21 Coolant Temperature Sensor

1993 legacy code 21 coolant temperature sensor clear wiring

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3 replies to this topic

#1 bopp



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Posted 30 April 2014 - 11:40 PM

I need your help, friends.


I have a '93 Legacy L wagon, 230k. Yesterday morning, after not driving it for 48 hours, it started very rough (almost couldn't get it started) and CEL was on. Drove to work and left a few hours later; warmer start was much better but still rough. My local shop did not have the right connector to read the CEL code but recommended a fuel filter; it had been 80k since replacement so I had them do it. Warm start was fine, but cold start later in the day was rough again.


Google and YouTube educated me on the awesome self-diagnostic mode on this car, and using this I figured out that the code is 21 - Coolant Temperature Sensor or Circuit. Upon inspection, the wires leading to the sensor were halfway chewed through (second time a squirrel has wreaked havoc now...). Tonight I cut, spliced, and plugged back into the sensor, thinking I'm golden. No go - still a rough cold start and CEL is on. Self-diagnostic mode reveals code 21 is still active.


I tried clearing the code, but was unsuccessful - either I'm doing it wrong, or the code is still triggering. (There is disagreement on the internet about how exactly to clear the codes...connecting the green and black lead pairs in different combinations, gas pedal down, to halfway for 2 seconds, then up...driving over 7 MPH for 10 minutes and then rev to over 2,000 RPM...I tried this....)


Need advice on how to proceed.


If the sensor is fine and this was a wiring problem, will I still get the rough start (due to the car assuming it is hot for fuel delivery?) until the code is cleared? If so, what's the correct procedure for clearing the code?


Could also be that the sensor is itself bad...but I want to make sure of this before replacement. I've read about testing it with an ohmmeter, but it's virtually impossible to get my multimeter leads in the right places without taking the thing out.


Thanks for your help!!!

#2 johnceggleston


    Lite Master of the Subaru

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Posted 01 May 2014 - 07:15 AM

dis connect the battery over night to clear the codes,

then drive the car.

if it comes back i would replace the sensor.



FYI: there are 2 sensors,

the 2 wire unit is for the ECU,

the single wire unit is for the dash gauge.


and of course i would double check the wiring as well.

#3 bopp



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Posted 01 May 2014 - 08:13 PM

Well, egg is on my face...my initial splice job came undone...sensor is fine and CEL is gone. :)

#4 willwright


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Posted 02 May 2014 - 11:24 PM

Man, I'm so glad that has never happened to any of us before :P lol

Also tagged with one or more of these keywords: 1993, legacy, code, 21, coolant, temperature, sensor, clear, wiring

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