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Problems/Service/RepairsIf you have a problem with your HHR, want a tip on repairing or performing a particular service to you HHR here is the place to post!
OK, don't bother to read the manual. Posts on the internet are more reliable. Why would the title reference the trim system if it didn't mean the trim system?
Yeah, but not every problem is a faulty alcohol reading. Why not use Occam's razor?
I did acknowledge that your theory is possible and explain the technical reason. Did that part get missed? Have you ever explained the mechanism that makes it a possibility?
Maybe, the alcohol % being higher than expected could be misinterpreted as too much O2.
When alcohol burns the byproduct is O2, that is how the computer figures the alcohol content. If the adjusted O2 does not agree with the expected the fuel trim is adjusted to make the A/F 14.7:1.
Of course, this assume closed loop has been achieved.
I know of a case where P0172 was fixed with a new fuel pump. Other cases have involved rusted vapor lines and stuck purge valves.
In other words: if the system is lean the trim will be rich and if the system is rich the trim will be lean.
Why would it mention alcohol content? My point is the Don seemed be saying I had the meaning of P0172… backwards, and seems to be using that (mis)interpretation to disprove the possibility of an erroneously high stored ethanol %. But he’s the one stating it incorrectly. Your link proves it.
P0172 means that (the ECM thinks that) the trim needed to correct an initial rich condition is excessive.
The situation of an excessively rich initial, i.e. open loop, a/f is adequately explained by an erroneously high stored alcohol %.
Could be something else. Why speculate. Just READ THAT STORED A/F.
No updates, my daughter is using it as is. Push and hold pedal to the floor and crank and it starts (a second or two of rough running). Then it runs perfectly.
I will check it out again soon and get the ethanol% read as soon as I have time.
It's been a long time since my original post. My daughter was driving it as is. Then she said it seemed to stop being hard to start once it got warm.
Now that inspection is due, I am trying to get rid of the MIL light, which is P0172.
I set my code reader to live info and looked at the oxygen sensor voltage, short term fuel trim, and Alcohol percentage. This is after the O2 sensor is warmed up.
The readings are stable for a few seconds after startup, then the fuel trim jumps wildly with a min of .1 to a max of -21.
The oxygen sensor voltage bounces in the range of 0.04 to .995.
The Alcohol percentage reads a steady 76.1%, no9 matter how many times I start the car.
Obviously, I need to get the alcohol percentage reset. Isn't this number supposed to be an active number that the car calculates as it goes?
