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CEL - Coolant Temp Sensor

donkeylips

Well-known member
Joined
Jun 18, 2009
Messages
552
Location
Rochester, NY
My ECU is throwing a code 21.

1. I checked continuity between the two wires at the sensor, and the coolant temp sensor pin (YG wire) and sensors ground pin (GB wire) at the ecu connector. Both had continuity.

2. I checked the resistance of the sensor - it seemed to be in the ballpark, between 1500 and 2500 ohms. Then I swapped in a spare used sensor that had similar resistance, and it still threw the code.

3. So finally I tried a different ECU, and that one throws the same code.

The car is running very rich and I can't get the CEL to go off. I am stumped here. It seems that I have checked everything relevant, unless both of my sensors were bad, which I doubt. Most everything is stock, besides a Walbro 255 pump (not rewired) with a factory fuel pressure regulator (no fuel pressure solenoid). Ideas?
 

turbowop

Well-known member
Joined
Apr 29, 2001
Messages
11,972
Location
Yakima, WA
You checked continuity but did you check resistance of the wires? It may be that one of the wires is hanging on by a single strand near the sensor where they get super brittle.
 

Specter

Well-known member
Joined
Apr 20, 2008
Messages
367
Location
Karachi, Pakistan
^ Yes that can be the case. Although i did not have any ecu code but while cleaning up my wiring mess i rewired the coolant sensor wires entirely because they were very brittle.
 

donkeylips

Well-known member
Joined
Jun 18, 2009
Messages
552
Location
Rochester, NY
I checked continuity with my ohmmeter. Resistance was low, but I'll double check. I have already re-wired it in the past. Maybe it didn't hold up too well.
 
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