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Check Engine Light, 51 Erorr

RumPunch

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Is there somewhere good here to run through diag of check engine light codes? I have a miss/stutter (all original injectors installed after issue with aftermarket ones) now I am getting a 51 error code. Do I need the emissions manual off line?
 


dirtymike

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Code 51 says the ECT signal failed at the high end(approximately 5.0 volts)failure mode indicates -40Deg. F.
 

RumPunch

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thanks. So possibly failed coolant temp sensor/switch? Wouldn’t think that would cause a miss.
 

dirtymike

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It will run the engine like its on choke, I think? ECU thinks its cold.
 

dirtymike

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194 deg F should be .60 volts with 2.80 ohms
 

dirtymike

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Back probe the ECT with a DVOM when warm
 

Uncle Gump

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Yeah... check ECT sensor connector for 5 volt reference first.

If good... check resistance across sensor @ whatever temp it is at... bounce that number off an ECT temp table.
 

Uncle Gump

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thanks. So possibly failed coolant temp sensor/switch? Wouldn’t think that would cause a miss.
Is it like a dead miss... or a random rich misfire.
 

RumPunch

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Random miss can gag on throttle and mostly go away. But low load/throttle input in gear falls on its face.
 

RumPunch

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4.68v key on 57.0k ohms across sensor, compare to original sensor, 58-59k ohms. Ambient temp (48 f ) this morning. I’ll trace down the signal output now.
 
Last edited:

dirtymike

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test the old one in boiling water. analog meter you can watch the needle move as the water heats up.
 

RumPunch

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See above just edited post comparing to original…
 

RumPunch

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Back probed didn’t have enough time this morning to get it up to temp but no volts out of the second pin so I will check original in water at op temp and see then get truck up to temp and compare if ok I’ll check signal wire back to ECU.
 

Uncle Gump

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For reference...

1652014517586.png
 

RumPunch

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Thanks gump
 

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