Merc 502 efi code 23 iat censor
 

I have a code 23 reading iat sensor . I says running at -32 degrees. I replace the iat sensor but still says the same thing even after clearing the code. Any suggestions

Check the wiring at the plug,,,, pins tend to pull out of the connectors

I did that and checked the wires

IAT = Intake air temp sensor. It is a 2 wire sensor. Tan and black. The purpose of it is measuring temp of the incoming air in the intake. It uses a thermistor to control the signal voltage to the ECM.

The ECM supplies the voltage to the sensor so when the intake air is cold the sensor resistance is high. When the intake air is warm the sensor resistance is lower and that's when the voltage drops. When key is just turned on (no start) the sensor voltage should be 5v sensor. When the engine reaches normal engine temps 160 to 180 degrees the voltage should drop at the sensor to 1.5 to 2 volts. Again the engine has to be completely warmed up to reach this correct operating voltage for the IAT sensor.

If I remember correctly tan wire for ECM - MEFI 3 should be pin J2-30 pin ECM / connector. The ECm supplies voltage on circuit 472 to the sensor. Again this is the 5v reference signal sensor. Black wire from the IAT MEFI 3 should be J2-3 - pin ECM / connector. If I recall MEFI 1 & 2 might be different pins / connector locations on the ECM. Not knowing your engine serial # can not say for sure what ECM you have.

Fault 23 is IAT voltage HIGH (open) or LOW (short) for MEFI 1 and if you have MEFI 2 or 3 fault code 25 would be IAT voltage low (short) and your fault code 23 is IAT voltage HIGH (open)

Your -32 reading is obvious that your voltage reading at the IAT is going to be very high. IMO you have a really bad connection somewhere in the circuit and or at the connector or pin #'s I gave you at the ECM. Also corrosion and or any moisture will cause this as well. Also want to ask where did you get your IAT as that might be a problem. Just saying. .

Last but not least afterwards - if all the testing of these related circuits and everything checks out then of course it could be the ECM itself being bad / internally opened or shorted. I wrote all of this so that it could be helpful in your task to hopefully clear up your issue plus it helps me to remember about how this stuff works since I do not see it daily like I use to.

did you ever figure out what was wrong? I have a similar issue where mine is reading -40.

If you have a open circuit, unplugged connector, damaged wire, etc, it will revert to lowest reading, fwiw