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2008 trailblazer 4.2.can someone tell me the feedback voltage on the potentiometer. I assume it is open or closed signal to pcm. Three wires 5 volt ref signal and a ground. What should signal voltage show when pump is running and solenoid is open? Shows voltage on my snap on and psi. How is psi calculated? Voltage was showing like 2.5 volts and 14.5 psi koeo. Thanks for any input.
Thanks I have all that. 2.55 koeo pressure sensor volts. Air pump on goes to 3.10 volts. Psi goes from koeo 13.9 psi to 15 5 psi with pump running. Don't know what normal is.
It's drawn as a potentiometer but it's a pressure sensor that reports to the PCM in voltage and the scan tool basically translates that to psi. Your reading of 2.5 volts and 14.5 psi is one and the same. Just observe the human readable pid, SECONDARY AIR INJECTION PRESSURE SENSOR (PSI)
KOEO, your psi and baro should be about the same. [strike]The PCM wants to see less than 10 kPa (1.45 psi or 2.9 inHg) of difference between that pressure sensor (in the air system) and your baro (that's on intake manifold).[/strike] So you wrote your sensor was reporting 14.5? That would mean your BARO is reading about 29, is that about right?
When you clear this code does it come back KOEO? Maybe this would indicate that one of the pressure sensors is skewed?
What should signal voltage show when pump is running and solenoid is open? Just observe the psi pid (SECONDARY AIR INJECTION PRESSURE SENSOR (PSI)). Service info states when normal air function occurs (pump on, solenoid open), the pressure should rise no more than 1.16 - 1.45 psi
So if your psi is 15 psi (nice round number) , add 1.45 to it … so the psi should be no more than 16.45 psi, with pump on and solenoid open.
When the pump is turned on but the solenoid closed, it expects the pressure to GO UP at least 2.9 PSI --- but no more than 7.25 PSI
DTC for incorrect pressure reading are snapshot while the car is running so if you're recreating with engine off, know this is not accurate.
Last edit: 4 years 1 month ago by jreardon. Reason: wrong info strike through
I am sorry I just read baro comparison on service information. Thanks for the detailed information. That helped explain everything. Will have to test. Thanks again. JOE
