Can p1781 be associated with power loss? - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect

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Old 11-20-2012, 01:38 PM   eBay Motors  #1 (permalink)
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Exclamation Can p1781 be associated with power loss?

Been having problems with my truck having a power loss. Took it for a drive today without the programmer and got p0380 u1000 and p1781. P1781 is new and I've never had it come on before. Anyway this could be the culprit?
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Old 11-20-2012, 03:48 PM   eBay Motors  #2 (permalink)
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You should try and do some research man.

Allison LCT1000 P1781 or P0802 Setting in the ECM - kw 6.6 8.1 code CEL DTC ECM GMT560 GMT800 intermittent L18 LB7 LLY light M74 MIL P1781 P0802 PCM repeat shift start TCM transmission #PIP3094 - (Aug 5, 2004)

Allison LCT1000 P1781 or P0802 Setting in the ECM

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:

Some customers may comment that the Service Engine Soon indicator lamp is illuminated. Technicians may find DTC P1781 (model years 01-02) or DTC P0802 (model years 03-05) (Transmission Control Module - Incorrect Voltage Level on MIL Request Circuit) stored in the ECM. This condition will usually occur during engine start up. This code sets when the ECM and TCM do not communicate properly on the initial "hand shake" during power up. One module may be powering down during crank due to a low voltage situation.

Recommendation/Instructions:

Note: For 2001 vehicles refer to TSB 01-06-04-020 for the latest ECM calibration. Check the vehicle for a possible weak battery or a dead battery in dual battery applications. Also check for possible poor battery cable connections, poor grounds, UBEC connections, or possibly an ignition switch dropping out during crank.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:

(01-05 Chevrolet Silverado) and (01-05 GMC Sierra) and ( 03-05 Chevrolet Kodiak) and (03-05 GMC Top Kick)
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Old 11-20-2012, 04:32 PM   eBay Motors  #3 (permalink)
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I've been searching and asking around about it for going on 4 hours and I've came across the service bulletin a few times and read it and also know what the codes mean. The posts I have found with symptoms like mine are usually with the truck having p1781 and p0101 for the MAF sensor or the truck has bad batteries and I've got new batteries (one is 6 months old and the other is 2 weeks old) and I've cleaned the MAF 3 times to make sure it's clean. I'm just trying to find out if the p1781 can be the culprit of my truck having no power since it it means the tcm has a problem with the "handshake" and maybe causing my tranny to rob all my power since the only other codes is u1000 when my predator won't connect and p0380 for glow plugs. Thanks
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Last edited by Stevenmc89; 11-20-2012 at 04:36 PM.
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Old 11-20-2012, 06:52 PM   eBay Motors  #4 (permalink)
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I say go to the auto parts store, buy a maf sensor, install it, and see if it changes anything. If it doesn't take it back and tell them you didn't need it after all. That way you can completely remove that from your list of problems.

Im not sure if the predator can reset your tcm but you deff need to look into resetting it,
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Old 11-20-2012, 08:26 PM   eBay Motors  #5 (permalink)
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I've been thinking about doing that when I get paid. It acts just like a bad MAF sensor or boost leak. It idles great, no smoke, no injector noise, no fuel in oil, no fuel smell in exhaust or anything strange but going down the road it feels like you have one hell of a load behind you. When on the way home from work going up a hill in 5th at 55mph the predator said 76% engine load so something is up
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Old 11-20-2012, 08:27 PM   eBay Motors  #6 (permalink)
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On resetting the tcm I'll probably need a tech II right?
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Old 07-13-2013, 11:45 PM   eBay Motors  #7 (permalink)
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Did you ever get this resolved? Im having a similar issue...
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