Check engine lights comes on when driving above 10,000' | Ford Explorer Forums - Serious Explorations

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Check engine lights comes on when driving above 10,000'

wazzles

Member
Joined
November 15, 2004
Messages
40
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0
City, State
Denver, CO
Year, Model & Trim Level
'97 XLT
Hi,

When I go up to the mountains from Denver to Silverthorne, CO the check engine light comes on after being up in the mountains over the course of the weekend. The check engine light stays on while I'm in the mountains. When I come back to Denver the check engine light goes off within a day of being back at a lower elevation.

I go through several mountain passes while I'm in the high country that can top out as high as 12,000'. Is the elevation causing this or all the stress that is being put on the engine from the climbing? Any help would be appreciated.
 



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the only way to know for sure is to read the code, but I'm willing to bet its either not getting enough O2 to satify the emissions sensors or smoe emissions valve isnt able to adjust enough to do what it needs to do


do you see significant fuel milage changes?
maybe you could borrow a code reader next time you make the trek
 






Fuel trim limits

The MAF sensor measures the mass of the air flow instead of the volume and is accurate from high altitudes to below sea level.

The PCM adjusts the fuel trims based on data from the O2 sensors. The higher the altitude, the less dense the air and the less fuel needed to maintain optimum air/fuel ratio. When the required fuel trim adjustments exceed predetermined limits a diagnostic trouble code (DTC) is set and CHECK ENGINE is illuminated. I suspect that is what's happening. When you complete a couple consecutive drive cycles at lower elevations with no fuel trim limits exceeded the CHECK ENGINE is deactivated. You can easily verify this with an OBD-II code reader.
 






Could be as simple as the fuel tank purge circuit. Again, you need to read the code to be sure. Whatever, it's not really a problem though. Factory just doesn't count on many of use being at altitude.
 






What brand of OBD-II code reader do yall recommend?

I don't notice a drop in fuel efficiency.
 






The MAF sensor measures the mass of the air flow instead of the volume and is accurate from high altitudes to below sea level.

The PCM adjusts the fuel trims based on data from the O2 sensors. The higher the altitude, the less dense the air and the less fuel needed to maintain optimum air/fuel ratio. When the required fuel trim adjustments exceed predetermined limits a diagnostic trouble code (DTC) is set and CHECK ENGINE is illuminated. I suspect that is what's happening. When you complete a couple consecutive drive cycles at lower elevations with no fuel trim limits exceeded the CHECK ENGINE is deactivated. You can easily verify this with an OBD-II code reader.

Are the fuel trim adjustments exceeding the predetermined limits due to something being broken on the vehicle?
 






Not normal

Are the fuel trim adjustments exceeding the predetermined limits due to something being broken on the vehicle?

Not necessarily. The predetermined limits may be established assuming a lower altitude operating environment.
 






That could be possible because the vehicle was purchased in Georgia (lower elevation).
 






That could be possible because the vehicle was purchased in Georgia (lower elevation).

Could very well be, Ford cars have a "DSO" district service office code on the door sticker. You can look this code up to find out where your car was originally shipped to. A car shipped to the Denver DSO is going to have a slightly different (high altitude) calibration from the Georgia or even Cali DSO. That is why dealers need a VIN if they flash your car. The limit on normal calibrations may be 10000', higher than that the low BARO parameter is probably flagged as failing MAF.
 






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