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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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  #1  
Old 05-20-2002, 05:38 PM
LarryM LarryM is offline
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Took my pickup into the dealer for some warrenty work today. Needed to fix loose weather strip under hood, put new pads on the rear overload leafs, fix leaking rear axle seal, and I wanted the latest reflash for the "Trussman Syndrom".

Got the call from the service guy and he tells me all is being fixed except I have the latest PCM/TCM programing (which I know I don't), but my fuel temperature sensor is defective. He claims this will effect transmission performance due to fluctuating fuel pressure. I guess if I'm short on power due to low fuel delivery, it would cause early downshift. Sure didn't seem like I was short on power though. There was never a SES light.

Anyone got an idea what this is really all about?
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Larry<br /><br />2001 2500HD, D/A, regular cab LS, 4x4, Wish it was a 6 sp!<br />2001 1500, regular cab LS, 4.3L, 5sp, wife\'s car!
  #2  
Old 05-20-2002, 07:46 PM
mark45678
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sounds like the TEC doesnt want to do a reflash? Its really hard to tell those guys that every one on the internet know more then they do..... BE CAREFULL HOW YOU WORD THINGS these guys have a lot of pride in what they do and most of the time it backfires if you tell them there job!!!! my.02
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Old 05-20-2002, 09:10 PM
Kennedy
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Sounds goofy to me. Maybe there was a history code (bogus) for the fuel temp fault. Now you mentioned pressure and temp sensors in the same paragraph, so keep that in mind.

Anyhow, the latest updates address false codes, and I am told that when one digs deeper, the update involves the bogus fuel tmp sensor codes. I would twist his arm to update, and then see what reoccurs...
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Old 05-20-2002, 10:27 PM
LarryM LarryM is offline
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I must admit that I am a bit confused.

The service writer indicated that a faulty fuel temperature sensor could cause fluctuations in the fuel pressure. He did not elaborate. I suspect because that's all the service tech told him.

When I checked the GM VCI web site for my VIN, the number that SteveO posted last month as being the updated calibration addressing 2-1 shift, shift business, and OD lockout did not appear. As I understand it, this would mean it is not available for my truck.

When I last had the thing in, they uploaded all the latest stuff, but that was back in November or December. (Paperwork in truck at dealers, can't check date) Since there are no dates listed on the VCI page, I have no idea what, if anything, I'm missing. The service writer was polite, but adamant that they checked my current revision levels and there were no updates available for my truck.
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Larry<br /><br />2001 2500HD, D/A, regular cab LS, 4x4, Wish it was a 6 sp!<br />2001 1500, regular cab LS, 4.3L, 5sp, wife\'s car!
  #5  
Old 05-20-2002, 10:56 PM
mdrag
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LarryM,

TCM updates are not listed on the GM website, only ECM updates are there. I've not heard of a site for the TCM updates...

IIRC, the 2-1 shift and OD lock-out are TCM updates.
  #6  
Old 05-21-2002, 08:07 AM
LarryM LarryM is offline
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I think I knew that at one time. CRS is a terrible thing, but I can't remember why!

If I recall the discussion about that update, there was a PCM calibration as well as a TCM calibration that needed to be done. I could only find a number for the TCM when I did a search. Looks like I'm going to have to do battle at the dealer again today.
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Larry<br /><br />2001 2500HD, D/A, regular cab LS, 4x4, Wish it was a 6 sp!<br />2001 1500, regular cab LS, 4.3L, 5sp, wife\'s car!
  #7  
Old 05-21-2002, 05:27 PM
LarryM LarryM is offline
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Update:

Got truck back from dealer this afternoon. Here's the results:

Wobbling belt tensioner is normal. First bearing with 0.125 runout I've ever seen that was "normal".

Overlaod pads replaced with new pads plus slip on cushions and spring leafs re-aligned.

New rear shocks ordered.

Under hood weather strip re-secured.

Excessive transmission downshifting and hunting determined to be possibly caused by defective fuel temp sensor. (Code PO181) Sensor replaced and tested OK. They still insist that there are no available software updates for my truck. This discussion wil be continued when I go in for the new shocks.

For what ever it's worth, it seems to have smoother power delivery and better response at the low end. Just seat-of-the-pants observations. I'll see what happens next week when I hook up the trailer and run 1500 miles at 16K GCW.
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Larry<br /><br />2001 2500HD, D/A, regular cab LS, 4x4, Wish it was a 6 sp!<br />2001 1500, regular cab LS, 4.3L, 5sp, wife\'s car!
  #8  
Old 05-21-2002, 05:34 PM
pinehill pinehill is offline
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LarryM,

Ask your tech to do a printout of the current flash. They can do this for you in about 5 minutes. Then compare it to what you see on the GM site.
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  #9  
Old 05-21-2002, 11:10 PM
Kennedy
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While it is definitely possible the sensor was bad, i kinda doubt it. Best way to tell would be to overnight it in the shop and key up to compare the reading to the other sensors.

The update for false codes MAY be only for the 2002 models.
  #10  
Old 05-22-2002, 07:08 AM
D-max Man D-max Man is offline
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LarryM,

On the 2001 model year, the fuel temp. is compared to the inlet air temp. (IAT) and if the difference between the two is too great, it will set the P0181.

The IAT is part of the Airflow Sensor, which is mounted in the air filter box. The problem is that it is right on top next to the hood. When the truck is parked and the sun is beating down on the hood, it will warm up the IAT so when you first start the truck, you will have a false IAT reading until the airflow cools it down.

This is what causes the P0181 code to set on the 2001 models even though there isn't anything wrong with the fuel temp sensor.

On the 2002 models, they reference coolant temp instead of inlet air temp to solve this problem

[ 05-22-2002: Message edited by: D-max Man ]</p>
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