Recently, my 2002 Duramax started acting up. When driving, I can hear what sounds like surging in the engine, or the injector rattle getting loud, then normal, then loud again. It's randomly off and on, and when the rattle is loud, the power decreases.

At idle, the engine RPM is surging or hunting. This is random as well, and happens now about 80% of the time. If I am at a stop light in drive, the surging is enough that the truck would lurch forward if my foot wasn't on the brake, (for that matter, the torque converter seems to want to lock up at this point). When I take my foot off the brake, and press the accelerator, in some instances, the RPM comes up a bit before the tranny grabs hold and it can be a sudden jolt forward. When coasting to a stop, the down shifts can also be very abrupt.

I put a code reader on and got the following:
P1781
P1621
P0380
P0118

After clearing the codes, I get P0380 and P0118 come back.

(Note: I have a glow plug broken off in the head when a shop tried to change the power strip. Hence the P0380, I think. And that's another huge issue since I live North of the 49)

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I found a fix while I was waiting... seems the ECT can cause a lot of strange problems when it goes bad. Replaced it this morning, and the truck runs like new.

 

P0118 - Engine Coolant Temperature Circuit High Input

this may be the reason for it running rough. check your ground points and harness for damage. also make sure your batteries and alternator are working properly. the TCM is one of the first to start acting up when the voltage is low (P1781 poor or lost communication to TCM)

correct the P0118 first then see what happens to the others, may clear on there own. sorry but i don't have the wiring diagram for an 02 so cant help much there.


never mind, i see you got it fixed

 

Thanks 2004LB7, I did fix that problem, but I am still chasing around wiring to see what else is corroded or damaged. Seems this truck had a rough previous life. The 1781 code is still a concern, I will keep looking.

 

check this out:

Subject: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)