GM Duramax DTC Diagnostic Trouble Codes Table

Diesel Articles

Use the "Duramax DTC Lookup" form immediately below to look up a specific diagnostic trouble code (DTC); or, scroll down the table for the same information.


The Best-Ever 6.5 Chevy Diesel Rebuild

Diesel Articles

A while back, Ted Rich, of Granite Falls, Washington contacted me about a rather unique 6.5 Chevy diesel engine build for his 1998 Chevrolet 3500 4x4 dually truck. Ted, like many of you, is a GM diesel enthusiast who loves his truck. He had spent a lot of effort and money over the years getting it built up exactly like he wanted. Unfortunately, after about 150,000 miles of happy service, his engine failed. Instead of buying a new Duramax replacement, Ted challenged me to build the most durable, smoothest running and efficient 6.5L Chevy diesel engine that I could imagine. A few extra horsepower wouldn’t hurt, he said, but sheer power definitely was not his aim. Diesel Depot – with our 10 years of experience building these engines for a wide range of applications from mild to wild – accepted Ted’s challenge and began this unique engine build. My thanks to Ted, he allowed me to use my imagination and to utilize some relatively new and exciting technologies to achieve our goals.

Duramax LLY Overheating and Thermal Feedback Primer

Diesel Articles

I love what I do, and that is a blessing. Focusing on the troublesome mysteries of the technical world, I get to figure things out: things that have no apparent explanation... the elusive.

What follows is one such mystery, wrapped in a clever disguise and hiding in plain sight for years. It remained undetected for so long because there is not a single vehicle sensor, diagnostic, or gauge that is set up to alert us to what I finally found with patience, a casual observation, a $15 gauge and a paradigm shift.

As you read, keep in mind that the principles in this article can be applied to all turbocharged vehicles, not just the Duramax. You may well find inspiration to look at other unsolved mysteries by the time we are done. If you do, I would love to hear about it.

Duramax LLY Disappointment

It was 2004 when the Duramax LLY model replaced the LB7. Promises of more power, an advanced variable geometry turbo (VGT), among other announcements, were considered worth the wait. Unfortunately, it became clear right away that there was a problem. The engine did not seem to live up to the promises. Economy was reduced, performance was hindered and many towing customers could not use it for the advertised load capacity. The vehicles even overheated. Compared to the first generation LB7 Duramax, the LLY seemed to be dragging an anchor behind it.


Steve Johns 6.2L Diesel Hummer H1

Diesel Articles

Steve Johns 6.2L Diesel Hummer H1

Steve Johns loves his 1993 AM General HMC4 (4-door hardtop), powered by the stock 6.2L naturally-aspirated diesel. After years admiring the AM General H1, five years ago Steve purchased this clean specimen from his local GMC dealer for $25,000.00. It had only 50,000-miles on the odometer.

Ninety-three was only the second model year for the civilian Hummers – basically modified military trucks. (You can see the tan military paint showing through on Steve’s Hummer where the factory white paint has peeled away.) This H1 includes a 12,000-pound. Warn winch, undercarriage protection, air-conditioning, rocker-panel protection, a brush guard, tow hitch, and the Central Tire Inflation System (CTIS). This truck has every factory option offered in 1993 except power windows and door locks.


Lube Notes: Petroleum and Synthetic Oil Base Stocks and Additives


Lube NotesIn the preceding Lube Notes, we covered basic lubrication, oil functions, additives and base stocks. Now, it’s time to construct finished lubricating oils. From what we have learned, it may seem like the only thing we need to do is pick a base stock oil, mix in some additives and presto, we have lubricating oil. If only it was that simple. Of course, it’s not.

Previously, we looked at the refining of petroleum and classifications for synthetic and petroleum oils. The base stock with which we choose to start will obviously have a direct bearing on the quality of the finished product. If cost is no concern, then all finished oils would be made using one of the synthetic base oils since they result in the best lubricating oils. However, cost is an important factor and will always be a consideration in choosing base stock oils. Most oils are manufactured by a reverse process where the final performance requirements dictate the quality or lack of quality of the ingredients. If the manufacturer is making an oil to meet the minimum performance criteria for the current classification, then no money will be spent on anything more than an adequate base stock. On the other hand, if the manufacturer is producing a high performance oil, then he will spend what is reasonably necessary to produce the final product’s higher level of performance.


Heating Problem After Replacing AC Pump

6.2/6.5 Issues and Answers

Our ’94 one-ton Chevy diesel seems to have a heating problem that we think began soon after we had the air conditioner pump replaced. The problem is, no one seems to be able to fix this for us. The temperature gauge goes up to 230ºF and back down; up and down it goes. It takes spells of swinging back and forth like this, then seems to be fine at other times. I am not convinced that it ever really gets hot, even when the gauge says it is. The mechanic at our dealership has replaced the thermostat, then the radiator, then the water pump, then the radiator hoses, then the temperature sensor, then the fan clutch and finally another new thermostat; all without solving the problem. After each visit, they tell me it is fixed and send me on my way with a lighter wallet, but the problem returns. Now, after all this expensive work has been done, we have noticed that the oil pressure gauge is reading lower than it used to and that the volt meter reads low. We also see that the speedometer jumps around when I rev the engine in neutral. Then, once in a while, the wipers will make an unplanned swipe across the windshield. Maybe I am being unfair to the mechanics, but none of these problems existed before the work was done. Understandably, I hesitate to take it back to the dealership for fear of the costs. Am I vexed? Can you offer help?


Problems with Lights on a 6.5L Diesel GMC

6.2/6.5 Issues and Answers

I have a question not related to my engine, but hope you can help. Our ’95 GMC has developed a variety of problems with its lights, while we were on a trip. The turn signals were sometimes dim and or they flashed rapidly. The brake lights often do not work at all and the tail lights are dim. All the lights are behaving oddly. A dealer checked it out for us and replaced many bulbs, but things are still goofy. He now says it needs a new turn signal switch at a cost of $620, but he will not guarantee this to be the fix. Do you have any suggestions?


Country and Model Year from VIN

6.2/6.5 Issues and Answers

I have a question about the VIN (vehicle identification number) on the GM trucks. What character in the vin tells the country of manufacture? What character tells the year model?


1998 Dually Smokes Like a Freight Train

6.2/6.5 Issues and Answers

Please help! We have a problem with our 1998 Chevy dually that has proven to be beyond the capability of mechanics, even so called diesel mechanics in our area. Our big red truck smokes like a freight train sometimes. It will be fine for a day or so then, when we need power most, it lets us down and only billows black smoke. So far, we have had to replace the turbocharger, catalytic converter thing, injectors, fuel filter and more – none of which fixed the problem. I am tired of trying to get results from people who seem to only be guessing; please help.


Allison Transmission Issues with Fifth Wheel Towing

Duramax Issues and Answers

I have a 2002 Duramax 6.6 turbo 2500HD and pull a fifth wheel (about 8500 pounds). I have been told there is a second filter inside the pan of the transmission that should be changed. Does the back pressure method of changing the transmission fluid do an effective job of cleaning this filter, if it has one? I have also been told that it is not a good idea to change the transmission fluid very often. Is this true? My transmission temperature reading gets above the 200ºF mark almost every trip during the summer months. Is this to be expected?



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