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Check engine light went on then off code 54


88ranger91

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Hi all just replaced motor and tranny. Runs and drives great now but the CEL Came on today very briefly. I checked the codes and all it came back with in koeo was 54 which is the intake air temp sensor. It's a new sensor and has about 50 miles on it. After the CEl came on I did notice that the truck was idling about 100 rpm higher and after doing the koer test it came back with code 12 AND 13 saying engine idle is too low and too high.

I put the old sensor back in and unplugged the battery to reset computer so hopefully that will solve my issue. If it doesn't what should be my next thing to look at?
 


88ranger91

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Also CEL hasn't been on since, even with the old sensor. Also I noticed the CEL stays on with the key turned on where as before I thought when you turned the key it illuminated and then turned off.
 

RonD

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CEL with key on is Computer running self-check, it can stay on until you start the engine.

IAT(intake air temp) and ECT(engine coolant temp) sensors are compared in the computer, a "sanity" check, to make sure both are within an acceptable range of each other.
ECT is the #1 sensor, so if it was off you could get IAT code, because IAT didn't fall in the temp range for ECT being at say 100degF(warm up).

ECT sensor also effects idle RPMs.
But I would clean the IAC Valve first to see if that fixes the idle issue
 

88ranger91

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Both are brand new sensors. If the old sensor doesn't fix the issue should I put the old coolant sensor in and see if that fixes it? If that doesn't fix it where should I look?
 

RonD

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ECT and IAT sensors share the same 5volt power from the computer.

Test that both are getting 5volts on one or their wires, key on engine off
And move the wires around while watching the 5 volts on the meter, make sure it isn't changing, should be a steady 4.90-5.10 volts
This is the Reference Voltage the computer supplies to sensors so the Return Voltage has meaning.
If Reference voltage changes then Return voltage changes, so has no "meaning" as far as correct Temp goes
 
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