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Old 11-24-2014, 11:37 PM   #1
jkennedy3489
 
Drives: 2009 Yaris
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Poor Gas Mileage, No CE Light but many codes

I noticed that my highway mileage has dropped to about 35 mpg so I hooked up the handy OBD monitor and had 16 codes!! These included Mass Air Flow Circuit Malfunction, Mass Flow Low and High Input, Throttle switch malfunction, Engine coolant high input temperature, o2 heater malfunction, crankshaft position sensor circuit malfunction, and of course the good old assorted cylinder misfire (yeah). But the car still runs OK! Had a new mass flow so I changed it out for good measure with no improvement. Any idea what I should try next. I was kinda thinking about the Crankshaft or O2 sensor. Should be interesting thanks!
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Old 11-24-2014, 11:40 PM   #2
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With that many codes, I would check the battery and alternator. Either of them failing could cause issues for the ECM.
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Old 11-25-2014, 12:07 AM   #3
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Thanks Scott for the cruise control DIY!! I installed mine last week and it works great! Back to my problem, I did check the battery voltage with a live OBD monitor and it showed good battery voltage with a slightly higher voltage from the alternator when charging.
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Old 11-25-2014, 06:26 AM   #4
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Originally Posted by jkennedy3489 View Post
Thanks Scott for the cruise control DIY!! I installed mine last week and it works great! Back to my problem, I did check the battery voltage with a live OBD monitor and it showed good battery voltage with a slightly higher voltage from the alternator when charging.
Try a different OBD code reader or go to a auto parts place and have them read it to see if it is just something odd with your reader.
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Old 11-25-2014, 08:19 AM   #5
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Luckily I have a second reader and it confirms the codes. It appears that these are extended codes that would cause issues with a pollution check but are not yet bad enough to throw an actual code. When I unplug any of the sensors I get an immediate check engine light so something in the system must be acting strange. It seems like all of the codes are connected except for the engine coolant high temperature. I am wondering if a O2 sensor not reaching temperature could cause all the rest.
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Old 11-25-2014, 08:26 AM   #6
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Originally Posted by jkennedy3489 View Post
Luckily I have a second reader and it confirms the codes. It appears that these are extended codes that would cause issues with a pollution check but are not yet bad enough to throw an actual code. When I unplug any of the sensors I get an immediate check engine light so something in the system must be acting strange. It seems like all of the codes are connected except for the engine coolant high temperature. I am wondering if a O2 sensor not reaching temperature could cause all the rest.
It seems very odd to have that many all at the same time, particularly on so new of a car. By any chance did they suddenly start after you did your cruise control install? It almost seems like you have a bad ground connection on the ECM.
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Old 11-25-2014, 09:57 AM   #7
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Good thought, I hadn't really considered this possibility as all of the wiring was already in place but it would be worthwile to disconnect and see if the codes go away. I will give this a shot tonight and let you know! The timing for the mileage change does coincide pretty close with the installation.
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Old 11-25-2014, 11:36 AM   #8
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Originally Posted by jkennedy3489 View Post
Good thought, I hadn't really considered this possibility as all of the wiring was already in place but it would be worthwile to disconnect and see if the codes go away. I will give this a shot tonight and let you know! The timing for the mileage change does coincide pretty close with the installation.
Ah, actually since you have an 09 you didn't mess with the ECM connector, so it really should not be that. Take a good look at your battery terminals for corrosion and at all of the ground straps (places where a wire is screwed into the chassis) under the hood.
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Old 11-25-2014, 03:14 PM   #9
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Quote:
Originally Posted by jkennedy3489 View Post
Good thought, I hadn't really considered this possibility as all of the wiring was already in place but it would be worthwile to disconnect and see if the codes go away. I will give this a shot tonight and let you know! The timing for the mileage change does coincide pretty close with the installation.
That would be my first move! Also check that nothing else was disturbed during the install.

Ive had my $10 cc on my 09 for four years now and its been flawless. I have the four momentary switches in a diamond pattern with ON up, SET to the left, RESUME to the right and CANCEL on the bottom. Its so easy to operate compared to the stalk mounted cc of others cars!
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Old 11-25-2014, 10:13 PM   #10
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I would suggest clearing the codes, and then checking to see which ones come back. Some of those codes may have triggered if your key was on when the sensor was unplugged. Do not start just throwing sensors at it, as it is VERY unlikely that they are all currently bad.
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Old 11-25-2014, 11:19 PM   #11
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Ok disconnected all the cruise control adds, checked battery connections and left battery negative lead off for ten minutes to make sure codes are cleared. Started it up and the codes came right back. Something is a little off!
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Old 11-27-2014, 11:23 AM   #12
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My ODB II reader gives all kinds of nonexistent codes for my Jeep. Take it to a parts place like Scott recommended...
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Old 11-27-2014, 09:55 PM   #13
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I typed a reply the other night but it didn't go through. I think you may be seeing "History" codes. Disconnecting the battery will not clear them. If you had any of the codes you mentioned, the CEL would be on.

Clear with a proper tool and re-inspect.
Cheers.
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Old 12-06-2014, 08:46 AM   #14
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Poor Gas Mileage, No CE Light but many codes

Definitely sounds like a bad ground.

There is one cluster bolted to the side of the head on the air box side. Unbolt that and sand the head and connector and put it back together. Also sand the gound on the battery and follow that wire to where it hooks to the transmission and chassis and sand both of those too.


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