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Old 04-04-2018, 03:10 AM   #1
terminal89
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Default Could bad transmission temp sensor cause weird shifting?

95 saturn SL1. Recently did a fluid/filter changed and noticed the wire for my transmission sensor was off. Probably knocked off during filter change. It had become greased up from nearby grease from failed CV axle. Cleaned it up and reattached sensor but now throwing a trans temp sensor code. Im also having hard shifting between gears once trans is hot. Does temp sensor affect shifting in saturns?
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Old 04-04-2018, 07:33 AM   #2
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Default Re: Could bad transmission temp sensor cause weird shifting?

While it's not the only cause of the issue you seem to have it's the simplest. Fix that, drive the car and let it relearn then see if things clear up. If not you move on to other things most likely being valve body
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Old 04-04-2018, 09:58 AM   #3
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Default Re: Could bad transmission temp sensor cause weird shifting?

Well I dont know what happened. I took my car to my mechanic to get his opinion (he's a family friend I trust). He cleared the codes from the system and took a test drive. Came back and said he didnt detect any hard shifting. I drove it myself and somehow he was right - the hard shifting that was there when I pulled it in the shop moments earlier was gone. And no changes besides clearing old codes out of the system. The only remaining code was an airbox sensor code which was fixed when I reattached it (it had apparently fallen off after airbox reinstall)

Dont know what to think now but I'll be happy as long as she continues to shift good.

One of the codes before clearing was 53 - knock sensor that can't be reconciled ECM? Hasn't reappeared.
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Old 04-04-2018, 10:00 AM   #4
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Default Re: Could bad transmission temp sensor cause weird shifting?

Transmission fluid temperature is correlated to line pressure, which changes the shift quality.

Low Line Pressure = Soft Shifting/Slipping Clutches
High Line Pressure = Harsh Shifting
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Old 04-04-2018, 09:24 PM   #5
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Default Re: Could bad transmission temp sensor cause weird shifting?

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Originally Posted by Saturn Night View Post
Transmission fluid temperature is correlated to line pressure, which changes the shift quality.

Low Line Pressure = Soft Shifting/Slipping Clutches
High Line Pressure = Harsh Shifting
Dunno what happened but issue resolved without even changing temp sensor. No issue with shifting or code now. Maybe Lucas treatment finally kicked in?
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Old 04-04-2018, 11:32 PM   #6
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Default Re: Could bad transmission temp sensor cause weird shifting?

When the temperature sensor was disconnected, the pcm detected it on the next engine startup and went to default mode - xmission hard shifts to protect against burning out clutch packs. Normal xmission shifts are a result of solenoid valves modulating hydraulic pressures for each shift, creating the smooth shifts we all come to expect from automatics. Losing a solenoid or temperature sensor forces the pcm to default programming - hard shifts until the problem is resolved. Reconnecting the sensor should have reset the error and return to normal shifts. Resetting the pcm allowed it to run as if it left the assembly line as a new car. It may be said that the pcm may have anywhere from 80%-90% of what it needs to run the engine and xmission with a driver simply driving for the pcm to learn the remaining 10%-20% on the fly. This isn't something I know. Its from the service manual.
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Old 04-05-2018, 12:06 AM   #7
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Default Re: Could bad transmission temp sensor cause weird shifting?

"It had become greased up from nearby grease from failed CV axle."

That has me a bit puzzled. The trans temp sensor is kind of under the spin-on trans filter at the front of the engine; pretty far from any of the CV joints. I don't see how CV grease could get to the temp sensor. Any chance there is confusion on which sensor that is?
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Old 04-05-2018, 02:52 AM   #8
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Default Re: Could bad transmission temp sensor cause weird shifting?

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Originally Posted by billr View Post
"It had become greased up from nearby grease from failed CV axle."

That has me a bit puzzled. The trans temp sensor is kind of under the spin-on trans filter at the front of the engine; pretty far from any of the CV joints. I don't see how CV grease could get to the temp sensor. Any chance there is confusion on which sensor that is?
No. The grease from CV axle removed and sensor cleaned up. The CV axle failed when torque mount failed. Torque mount dug into CV axle boot and tore it up

Last edited by terminal89; 04-05-2018 at 03:04 AM.
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Old 04-05-2018, 03:11 AM   #9
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Default Re: Could bad transmission temp sensor cause weird shifting?

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No. The grease from CV axle removed and sensor cleaned up. The CV axle failed when torque mount failed. Torque mount dug into CV axle boot and tore it up
The torque mount I removed was split in half. DEA industries. Replaced with Anchor 3X heavier than aftermarket and similar to OEM
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Old 04-05-2018, 03:59 AM   #10
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Default Re: Could bad transmission temp sensor cause weird shifting?

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Originally Posted by fdryer View Post
When the temperature sensor was disconnected, the pcm detected it on the next engine startup and went to default mode - xmission hard shifts to protect against burning out clutch packs. Normal xmission shifts are a result of solenoid valves modulating hydraulic pressures for each shift, creating the smooth shifts we all come to expect from automatics. Losing a solenoid or temperature sensor forces the pcm to default programming - hard shifts until the problem is resolved. Reconnecting the sensor should have reset the error and return to normal shifts. Resetting the pcm allowed it to run as if it left the assembly line as a new car. It may be said that the pcm may have anywhere from 80%-90% of what it needs to run the engine and xmission with a driver simply driving for the pcm to learn the remaining 10%-20% on the fly. This isn't something I know. Its from the service manual.
This seems most probable. I used to have a valve body code that would appear after 20 minutes of driving. It doesnt appear now. This was when the car was healthy and shifting good before issues. Car is shifting good now.
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