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post #1 of 17 (permalink) Old 03-12-2012, 04:43 PM Thread Starter
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High RPMs at Overdrive Speed

I have an '07 Cobalt that had been running great until recently. When I'm on the highway at 70 mph or so, my rpms are running around 3200. Until recently, they had been running around 2500. It's like the car won't shift into overdrive, but I've had it into a couple of different shops and both have not been able to find an issue with the transmission. The gas mileage has taken a huge hit (around 32 mpg to 25 mpg). Any ideas?
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post #2 of 17 (permalink) Old 03-12-2012, 07:07 PM
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It's your torque converter not locking up. Look at TCM or harness. Also if transmission oil is low torque converter will not work. You might also want to verify coolant temperature display to make sure it reads around 190F. If it is low or reads --F (If this circuit is not malfunctioning) torque converter will not work because ECM thinks transmission is too cold.

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Last edited by Coby7; 03-13-2012 at 08:56 AM. Reason: Clarified for MP81
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post #3 of 17 (permalink) Old 03-13-2012, 05:16 AM Thread Starter
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One of the shops said the torque converter was locking. Not sure how they knew but assumed they had a way to test that. Haven't really paid attention to the coolant temp. I'm in Minnesota so it might be possible when I'm at highway speed there's enough cold air flow to keep the temp down.
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post #4 of 17 (permalink) Old 03-13-2012, 05:24 AM
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Quote:
Originally Posted by Coby7 View Post
or reads --F torque converter will not work because ECM thinks transmission is too cold.
It will still lock, even if it says that.

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post #5 of 17 (permalink) Old 03-13-2012, 06:47 AM
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I'm refering to engine coolant temperature sensor not ambient temperature sensor. Coolant temperature has to reach 80C or 175F before Torque Converter lock-up. Of course throttle position and speed are also a factor.

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Last edited by Coby7; 03-13-2012 at 06:51 AM.
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post #6 of 17 (permalink) Old 03-13-2012, 07:05 AM
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Quote:
Originally Posted by Coby7 View Post
I'm refering to engine coolant temperature sensor not ambient temperature sensor. Coolant temperature has to reach 80C or 175F before Torque Converter lock-up. Of course throttle position and speed are also a factor.
I'm aware.

Mine doesn't give me a coolant temp reading most of the time. Converter locks up just fine.

1986 Chevrolet Camaro IROC-Z - Wrecked/Sold
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2007 Chevrolet Cobalt LT - M62 Supercharger, Ported Throttle Body, 42 lb/hr Injectors, Intense 2.9" Pulley, Cobra Heat Exchanger, SS/TC Exhaust, TTR Engine and Trans Mounts, Trifecta Tune, ZZP Header and Downpipe, '08+ FE5 Struts/Shocks, SSC Springs, FE5 Control Arms, SS/SC Front Swaybar, Powell Hardcore Rear Swaybar, 18" MSR 045s, Dunlop ZIIs, Nightshaded Tails/Side Markers, Shorty Antenna, Black Bowties, Black Grilles, Black Headlights, Dual JL 12" w1v2 Subs, A/D/S Front/Rear Speakers, Pioneer 7" Touchscreen, G85 Recaros, Leather Rear Seats, 160 MPH Cluster.
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post #7 of 17 (permalink) Old 03-13-2012, 07:55 AM
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Even if your display reading doesn't work it doesn't mean your sensor isn't working. It is one of the criterea for torque lock-up.

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post #8 of 17 (permalink) Old 03-13-2012, 07:59 AM
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Correct, so they correct thing to say would be make sure your CTS is working, because if the reading is ---*F, it could be working, or could not.

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post #9 of 17 (permalink) Old 03-13-2012, 08:44 AM
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Spliting hairs. Here's the list for TCC lock-up. It could also be the TFT sensor but these are not known to go bad in these transmission. Hope that it's not TFT because transmission has to come apart to change it.
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Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

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Last edited by Coby7; 03-13-2012 at 10:17 AM.
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post #10 of 17 (permalink) Old 03-13-2012, 10:00 AM
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Quote:
Originally Posted by Copper07 View Post
I'm in Minnesota so it might be possible when I'm at highway speed there's enough cold air flow to keep the temp down.
Not if thermostat is doing it's job.

Every minute spent angry is a happy minute lost for ever and ever!!!
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Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

Never drive faster than your guardian angel can fly
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