Engine cut out while climbing mountain pass

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particleman

Member
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CX-5 Touring AWD, Tech package, Metro Grey
While climbing a mountain pass on I-70 in Colorado (Vail pass, for those that are curious) on Sunday night, I lost power in my CX-5. It was pretty cold, maybe 10 degrees, and the road was somewhat covered in snow. Because the CX-5 has trouble getting up the I-70 mountain passes above 50 mph, I had it in auto-stick mode in 3rd or 4th gear at about 5000 RPM. I can't remember if it was 3rd or 4th, but the revs were definitely in the 5000 range the whole time and we were going about 50 mph. All of a sudden, the engine stopped responding and the traction control and TPMS indicator lights came on. Since we were going uphill and we were moving only on the car's momentum, I barely had enough speed to get the car onto the shoulder before someone rear-ended us.

Once on the shoulder, we turned the car off, waited a minute, and restarted. The traction control and TPMS lights stayed off after the initial start sequence. I checked the tires and they all seemed fine. The engine worked and we drove on the shoulder for a while until I was confident the car would make it up the mountain, and we got home safely.

Definitely a scary experience, and since I'm nearing 10,000 miles anyway, it's time for a checkup. I don't mind climbing a mountain slower than other cars, but I just hope the loss of power we experienced was a fluke. If there had been more traffic or if someone were right behind us, it could have been bad. Hopefully this hasn't happened to anyone else, and it was just my car or my driving that did it.
 
Hmmm...only thing I can think of, you hit a slick spot, and wheel slippage occurred.

TC and TPMS dummy lights in the inst. cluster would seem to support this, as slippage would be detected by wheel speed sensors, which TC and TPMS use as a core of their function/input.
One of the parameters of the vehicle's stability control system, I believe, is to close the throttle body when wheel slippage is present. I imagine the fact that you were at such a high RPM only compunded the problem.
 
Wheel slippage would engage the AWD.

On my xtrail i don't have TC, just AWD.

Sounds more like an electrical gremlin, have a quick poke around under the bonnet looking for any loose connectors, you may just be lucky.

If you have had a recent service, look in the areas the mechanic has worked, sometimes a engine sensor is disturbed.
 
Traction control cuts revs to prevent wheel spin. But it sounds like it totally cut out because you just rolled by momentum over to the side of the road. Did you take your foot off the gas?

Personally I wouldnt keep the engine highly revving while in snow. Its too easy to lose control and not be able to regain it because the gassing it would be too sensitive at that point.
 
xtrailman said:
Wheel slippage would engage the AWD.

On my xtrail i don't have TC, just AWD.

Sounds more like an electrical gremlin, have a quick poke around under the bonnet looking for any loose connectors, you may just be lucky.

If you have had a recent service, look in the areas the mechanic has worked, sometimes a engine sensor is disturbed.
Click to expand...

Only the rear LSD would "engage" when slippage occured. Otherwise, the AWD system is proactive, and delivers power to all corners near continually, though it serves a front wheel bias. If certain paramters are met, more torque can be delivered to the rear, and in this case (high RPM, high load), I would think those parameters are met. I believe the CX-5 features DSC, correct? Either DSC or TC is able to modulate the throttle plate, which obviously reduces output. But also, the ECU is able to modulate the HCU to apply brakes to individual, slipping wheels...

The key here, I think is that it was a high load situation on a slope. The car, I don't believe, can differentiate a level surface with an incline...
 
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IHeartGroceries said:
The key here, I think is that it was a high load situation on a slope. The car, I don't believe, can differentiate a level surface with an incline...
Click to expand...

I have read that the hill start assist only works if the hill is steep so it can measure inclines...
 
Were you low on fuel or maybe there was ice in the gas tank. The ice could clog the fuel pump temporarily if the fuel level was low. I can only imagine how reduced the power must be at your elevation because I live and drive in most places where I'm under 500 ft. If I had my CX5 running at 5000 RPM, even up a hill in third gear, it would accelerate very quickly to 100 mph. The throttle body could have iced up too if it were partially closed while the engine had high vacuum.
 
Just got a call back from the dealer. Here is what they think happened based on the computer codes.

The battery died a few months ago because I left a light on. Had it jumped, and all was fine.

However, the alternator in these cars does not recharge the battery. It just gives it enough juice to start the car and run basic operations. Mazdas are voltage-sensitive. They really want a full battery. So since my battery was not fully charged, when it finally came time to run the traction control for the first time (icy conditions uphill), the computer looked for voltage to run the TCS, but there was not enough voltage, so it killed the engine. The tech admitted it doesn't make sense, but that's what it does. They recharged the battery to full capacity, so I'll check it out again this weekend when i go back to Vail over Vail pass. We'll see how it goes.

To answer the other questions - He did not mention anything about the high revs, but I agree, probably not the best idea to keep it at 5k. I'll shoot for a lower rev next time. I just get annoyed when the transmission ping-pongs between hi and low gears and keeps dropping gears when it's looking for more power.

When the engine cut, i hit the gas, but nothing happened. It was as if the car was off.

There was about half a tank of fuel, and this happened about 30 minutes into the drive, so my instinct is that the fuel was warmed up by then. Vail pass is at about 10,000 ft. at the summit, so the car is definitely not as fast as it would be at 500 ft. Also, the grade is 7-8%, so pretty steep. All in all, probably not ideal conditions for an engine like this!
 
particleman said:
Just got a call back from the dealer. Here is what they think happened based on the computer codes.

The battery died a few months ago because I left a light on. Had it jumped, and all was fine.
Click to expand...

particleman-Thank you for the followup report, could be helpful to other owners.

What light was left on that killed battery?

Interior lights have auto-off (programmable) feature...
 
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Particleman - I sometimes test/dry the brakes near the top of a big hill in wet conditions to make sure they are dry and ready for use on the way down. If you do that with while the gas pedal is engaged the CX-5 computer is programmed to shut the engine down until you come to a full stop and turn on dash error lights. This is to eliminate the possibility that you hit the gas by accident and are really trying to stop the car. If you happened to have done the brakes while pressing the gas at the top of your hill, the car stopped and lit up the lights as designed and requires you to stop the engine to clear the lights. You can dry the brakes just take you foot off the gas when you do. Don't ever brake with your left foot while engaging the gas with your right or the computer gets real confused and requires you to come to a full stop to restore power...
 
The alternator is controled by the master computer and its output/drain on the engine is set up to engage fully in throttle off conditions for battery recharge. It provides limited electric power out when the engine is under load. This strategy uses free coasting, engine braking energy to fully charge the battery while engine output and efficiency is maximized. The extra long climb with high throttle demand and an already weaker battery could contribute to causing the situation. However, it is unusual that at 5000 engine rpm the alternator would not at least provide enough juice to maintain the voltage and keep the system running. There seems to be a bit of the i-ELOOP strategy implemented here and perhaps not too effectively for a large mountain pass...
 
Also wondering on the alternator not charging the battery ??

I would understand if the battery died just a few minutes before TCS engaged but it happened a few months ago.
 
GAXIBM said:
However, it is unusual that at 5000 engine rpm the alternator would not at least provide enough juice to maintain the voltage and keep the system running. There seems to be a bit of the i-ELOOP strategy implemented here and perhaps not too effectively for a large mountain pass...
Click to expand...

Sounds like flawed logic to me. If a weak battery in unacceptable then the program should change to charge the battery when it is weak, even if the engine is under load. When the battery is sufficiently full, then the alternator can go back to min output mode.
 
ALafya said:
Sounds like flawed logic to me. If a weak battery in unacceptable then the program should change to charge the battery when it is weak, even if the engine is under load. When the battery is sufficiently full, then the alternator can go back to min output mode.
Click to expand...

If this turns out to be a common problem it can be fixed with a program update...
 
CX-SV said:
particleman-Thank you for the followup report, could be helpful to other owners.

What light was left on that killed battery?

Interior lights have auto-off (programmable) feature...
Click to expand...

It was an interior light I believe. That, or some of the interior electronics (stereo?) managed to stay on. The battery was totally drained. I was gone for about 3 hours and got back to a dead car.
 
particleman said:
It was an interior light I believe. That, or some of the interior electronics (stereo?) managed to stay on. The battery was totally drained. I was gone for about 3 hours and got back to a dead car.
Click to expand...

That's troubling, because we don't know exactly what light or accessory caused the battery drain in 3 hours....
 
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