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Allison OEM Discuss repairing & maintaining an OEM Allison automatic transmission.


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Old 06-23-2019, 01:05 AM   #1 (permalink)
MIKAHC38
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Transmission shifting issues

I have a 2002 Duramax LB7 that is completely stock. I noticed the other day when I would accelerate my truck is having issues shifting gears. Seems the RPMs either remain the same or even go down a little when shifting up and transmission stays in same gear. It acts like the truck bogs down. If I let off the accelerator and then get back on it - it will finally shift. I noticed today while driving it that the trans temp gauge took a while to get to normal operating temp. I noticed too at different times the trans temp gauge erratically flicker up and down. Not sure if it is a shift solenoid problem or a wire harness problem. I do not have any check engine lights. I cannot accelerate going up hills either.

I changed the tranny fluid and filter tonight in hopes it would help but it didn't.

Any ideas, suggestions of what could be wrong is greatly appreciated.

Thanks,

Mikah

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Old 06-23-2019, 04:20 AM   #2 (permalink)
davester
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Maybe check for codes from both the engine and the transmission (which requires more than a basic ODBII code reader). Codes can be set, even if the check-engine light remains off.

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Old 06-23-2019, 10:03 AM   #3 (permalink)
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Can any auto parts store like Autozone or O'Reilly correctly pull and read the codes? Or have to get the codes read from somewhere like a dealership or auto repair shop that has a specific type/kind of scanner?
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Old 06-23-2019, 10:12 AM   #4 (permalink)
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Quote:
Originally Posted by MIKAHC38 View Post
Can any auto parts store like Autozone or O'Reilly correctly pull and read the codes? Or have to get the codes read from somewhere like a dealership or auto repair shop that has a specific type/kind of scanner?
You can ask the parts stores if they have a scanner capable of pulling TCM codes for you.
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Old 06-23-2019, 10:17 AM   #5 (permalink)
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Ok. Thanks.
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Old 06-23-2019, 07:09 PM   #6 (permalink)
MIKAHC38
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I took it to a local auto parts store this afternoon. They had a Bosch scanner. It did not find any codes. Came back clean. So not sure if maybe the Bosch scanner isn't advanced enough. I did see on the output display when they scanned for codes it listed an entry for TCM but the result was (0).

I am going to try and find a local repair shop that hopefully has an advanced scanner to scan it tomorrow.

Anyone know if the Bosch scanner is advanced enough scan tool to pull TCM codes? If it is and there were no TCM codes... not sure what could be wrong with my transmission shifting issue.
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Old 06-23-2019, 10:06 PM   #7 (permalink)
Ron Nielson
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The Bosch scanner that O'Reilly uses is capable of reading transmission codes. Whether the person that operated the scanner may, or may not, have been able to correctly use the scanner to obtain those codes.The scanner is only as good as the person using it.
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Old 06-24-2019, 07:02 AM   #8 (permalink)
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When was the fuel filter last changed? If it been a while, change it.
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Old 06-24-2019, 12:28 PM   #9 (permalink)
MIKAHC38
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It was changed about 4 months ago. Didn't think about it being a fuel delivery related issue. I am going to take it to a local repair shop to see if they can pull codes and check fuel rail pressure to see if it might be fuel delivery related.

I guess it is possible a bad fuel filter, fuel pressure regulator, or a bad CP3, or bad fuel hoses somewhere. Truck is a 2002 and completely stock and everything is original.

In 2009 I did have the injectors replaced under GMs special policy. Only other thing replaced on truck in 17 years is the water pump and alternator and a couple sets of batteries.

So I can't really complain.

About 5 or 6 years ago I did replace the fuel hoses into and out of the fuel filter head assembly and the short fuel feed hose because they were dry rotted and sucking air in causing me to lose prime.

Maybe other fuel hoses near the CP3 need replaced possibly due to age..

Dunno..

Hopefully this repair shop can run some fuel pressure tests and lull codes to see if it is fuel delivery related.

Thanks for the idea and suggestion.
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Old 06-24-2019, 06:16 PM   #10 (permalink)
MIKAHC38
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Quote:
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When was the fuel filter last changed? If it been a while, change it.
You may be on the right track. Auto repair shop snap-on scanner reported low fuel pressure. May be fuel filter or leak in fuel filter head assembly. No hard starts though. But I guess I will try these first.

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