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I am a high school auto shop teacher. We currently have a 2003 Buick Century in our shop that belongs to another teacher. It came in for a check engine light and has a P0405 code which is EGR position sensor low voltage. The students and I have verified that the sensor is missing a 5V reference as we are showing 0V on scan data and 0V on the actual signal wire and 5V reference wire from the EGR. I explained to the students that this could be a short circuit, an open wire or less likely but possible a connection within the PCM. I explained that I did not think it was a short because no other sensors were showing codes and there are no driveability issues. We further proved this by jumping 5V from the reference wire for the TPS to the 5V reference on the EGR and the sensor functioned as it should with 5V applied to the reference wire of the EGR. (If this was not a good idea to do I am open to hearing that. I was a little skeptical about doing this test but it worked out) We do still need to go to the PCM and see if we have 5V there. We have not gotten that far yet.
That all leads to my question which is more related to fundamentals. The wiring diagram shows that this is a solenoid and the operation description in alldata states that it is a PWM solenoid. Bi directional controls on the scan tool you allow us to control % from 0-100 percent all consistent with a PWM solenoid. What I am having trouble explaining to the students is why a PWM solenoid has a position sensor on it and why that position sensor reads a steady sweep from .7-4.5 volts as percentage is increased. Is the voltage from the position sensor actually pulsing as well and I am reading a steady voltage because of refresh rate on the meter? I want to be able to properly explain this to the students. Any explanation would be helpful. Thank you in advance.
The position sensor signal voltage is linear because result of the PWM on the solenoid is linear operation of the solenoid.
The solenoid doesn't rapidly open and close, rather it achieves desired opening position by way of PWM.
Spring tension holds the valve in the closed position.
The greater the commanded pulse width, the greater "available" voltage, the more the solenoid will pull against the spring untill the desired position is reached.
I thought I would post a follow up even though its not related to my original question because it was an interesting one. This was the cause of the fault. It appears a critter had gotten into the air box and chewed the reference wire for the EGR position sensor. Very strange that that was the only wire he seems to have gotten to by the time he got through the tape.
Thank you for the follow up.
I always wonder when I find one wire chaffed through or chewed up, "what are the odds it was THAT circuit?".
We use peppermint to discourage rodent activity on limousines that are put down for any period of time.
If nothing else, at least it smells better than squirrel piss alone
