ECM Electronic Control Modules, Trouble Codes & Code Scanners

OBD Code List

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Link to GM OBD-II Diagnostic Parameters

This link has downloadable pdf's of all the diagnostic parameters for many of our trucks. Not all years are there.



 

Note for Duramax Owners:

The difficult part of doing a Duramax conversion is handling the electronics. Many owners are purchasing complete Duramax drivetrains out of GM pickups and dropping them into their Hummers. Evidently there are many safeguards built into the Duramax computer system that will keep the engine and transmission from running. The issues are theft control lockouts and the need for all the inputs to be present. A company out of New Zeland called EFI Live has a code scanner and tuner that allows you to do what you want with the ECM.


Engine Computers

1996 TD owners can update their existing PCM to a 1997 or 1997 1/2 calibration (all later years have the more powerful curve and specs but you might as well use one of the 97's since they are easy to get and your truck is more similar to them). Both calibration files have timing and fuel delivery curves which will provide approx. 195 SAE net HP @ 3,500 RPM and 430 ft lbs of torque @1700RPM instead of your 190hp and 385 ft lbs torque.

You must first overcome the PCM's need for a 'Wait Lamp" input as the control of said lamp changed between 96' and 97' and up. Performing the following will accomplish this:
Locate the Blue 32 pin connector on your PCM.
Locate pins C7 and C12 in this connector.
Make a jumper wire to go between these two pins. You should also put inline a resistor or diode to create a small voltage drop.
I would use a 1N4001 Diode (Radio Shack #276-1101) with the silver band toward pin C7. The "Wait"lamp is approx. an 8 ohm bulb, the diode will drop the voltage to the PCM by 0.5V so it doesn't see a direct short. This will prevent a DTC P1643 from turning on the Malfunction Indicator Light and storing in long term memory.

You must then have the PCM flash programmed by any GM dealer with a "Techline " subscription but you must provide a valid 1997 or 1997 1/2 HUMMER VIN # or this will not work. The techline network will provide the eprom flash file and a Vetronix Tech II scanner can do the flashing which most dealers will have. Copy the VIN from any Hummer of the proper year or get a vin off a for sale truck on ebay.
The calibration file that will be down loaded should be 09355145 (for 1997 model year, other years will be different) and this will appear on scan information under CAL I.D. if performed properly.

Note: 1997 and up engines have various improvements including oil cooled pistons and cooling system changes. As long as you do not operate your 1996 for extended periods at wide open throttle such as pulling heavy loads up very long grades it will not harm your engine. The new curves really only add power at large throttle openings when it's needed. The upgrade will give you more pep on acceleration and when you need the extra torque on hill climbs, mud and sand etc. I have had this mod on my 1996 TD since the summer of 1998 with no problems. It does not run any hotter than before. Just use common sense, same as you would if you installed a performance PCM from some supplier.

More ECM Notes:

The 1996 system is different from all of the later years in the way the PCM interacts with the glow plug controller/ wait light. The people who market the performance/recurved for more power PCM's either do not know this or neglect to mention it. All of the later years can bolt on the new PCM and not have the problem.

You have several choices. Return that PCM and go back to a stock PCM programmed for your 1996, modify a stock PCM as described below or do the part below in bold with the PCM you are trying to use now which should take care of your problem. I have also included info on a fast idle mod you might want to do while you have things apart. I would use the new connector pins you will get for the idle mod to replace the old ones when you install the Diode/jumper wire. You can actually use the diode it's self for the jumper wire depending on the length of its leads.

"1996 TD owners can update their existing PCM to a 1997 or 1997 1/2 calibration (all later years have the more powerful curve and specs but you might as well use one of the 97's since they are easy to get and your truck is more similar to them). Both calibration files have timing and fuel delivery curves which will provide approx. 195 SAE net HP @ 3,500 RPM and 430 ftlbs of torque @ 1700 RPM instead of your 190hp and 385 ftlbs torque.

You must first overcome the PCMs need for a 'Wait Lamp" input as the control of said lamp changed between 96' and 97' and up. Performing the following will accomplish this:
Locate the Blue 32 pin connector on your PCM.
Locate pins C7 and C12 in this connector.
Make a jumper wire to go between these two pins. You should also put inline a resistor or diode to create a small voltage drop.
I would use a 1N4001 Diode (Radio Shack #276-1101) with the silver band toward pin C7. The "Wait"lamp is approx. an 8 ohm bulb, the diode will drop the voltage to the PCM by 0.5V so it doesn't see a direct short. This will prevent a DTC P1643 from turning on the Malfunction Indicator Light and storing in long term memory.

You must then have the PCM flash programmed by any GM dealer with a "Techline " subscription but you must provide a valid 1997 or 1997 1/2 HUMMER VIN # or this will not work. The techline network will provide the eprom flash file and a Vetronix Tech II scanner can do the flashing which most dealers will have. Copy the VIN from any Hummer of the proper year you can find or get a vin off of ebay.
The calibration file that will be down loaded should be 09355145 (for 1997 model year, other years will be different) and this will appear on scan information under CAL I.D. if performed properly.

Note: 1997 and up engines have various improvements including oil cooled pistons and cooling system changes. As long as you do not operate your 1996 for extended periods at wide open throttle such as pulling heavy loads up very long grades it will not harm your engine. The new curves really only add power at large throttle openings when it's needed. The upgrade will give you more pep on acceleration and when you need the extra torque on hill climbs, mud and sand etc. I have had this mod on my 1996 TD since the summer of 1998 with no problems. It does not run any hotter than before. Just use common sense, same as you would if you installed a performance PCM from some supplier."


OBD Diagnostic Software and Code Scanners


by Steve Yee:

To read and clear codes - any simple OBD2 Code reader will suffice. I've used an Inova OBD2 scanner for years, and I still use it when I want to do a quick and dirty check.

To read the actual sensors specific to the L56/L65 engine in your H1 (and even your two BMW's), you need a more advanced scanner, which includes the Tech2 and other advanced scanners or scanners/laptop combos from AutoTap, AutoEnginuity, and SnapOn's MT2500.

I personally use the AutoEnginuity scanner, attached to either a Compaq TC1100 or a Motion Computing M1300 tablet computer. It's able to do nearly anything a Tech2 can do, and is far cheaper than buying a Tech2. The AutoEnginuity scanner is tested against Hummers constantly as they upgrade (Clarke Ferber and myself both have contributed our trucks to the upgrade testing cycles) and is recommended by many BMW enthusiasts as well. I use it to tweak my wife's BMW E38. The latest upgrade also allows me to do transmission code reads as well as read the Duramax LB7 (and I think LLY) engines now.

The AutoEnginuity is capable of bi-directional controls, including TDC offset learn. If you are using version 4 or above, you will see a small tab at the bottom left hand side of the screen. It is labeled "Actuation", click on it and you can initiate the TDC offset learn from there. Your engine MUST be at normal operating temperature.

Others have used the SnapOn MT2500 with great success. It's another good scanner that has an excellent track record. One owner commented " I have a total of 250 bucks into my Snap on MT 2500 with software up to 2001. It works great for codes, and also gives engine and tranny info. You can do bi directional communication with it to turn things on and off."

Frankly, it all depends on the amount of money you want to spend. Tech2's list out at 5k. eBay sales for a Tech2 are around 3k (when they are available - which is rare). You should also buy a subscription to update the software on it, which I've never priced out. A SnapOn MT2500 with all the needed accessories will set you back about 800 for a used set, with no update subscription.

Autoenginuity (and most of their competition that uses a scanner/laptop combo) is about $350 for the GM sensor package plus the basic OBD2 reader. Toss in a cheapie laptop (A Toshiba L25-S1216 with XP can be had for under 500 dollars), plus free updates for life, and you're ahead of the game there.

AutoEnginuity Comments:

I discovered I can load the enhanced sensor database if I enter 1998 H1, 6.5L L56, Product C, Trans 4 speed. So far, there is not any database for the 1997 model year. I did take a quick look at the 1998 sensors and V 4.0 looks to be a big improvement. It now includes the transmission system as well as time set, etc.

I recently purchased the autoenginuity package which is very similar to what you have. It has all kinds of functions and to me as a mechanical layman the learning curve is pretty steep even though my neighbor that rebuilds older model Corvettes is in love with the software and all of the data which is quite comprehensive and I am learning as much as I can about how I can use it as a tool to maintain my vehicle. It is nice to be able to determine the causes of check engine lights.

I bought the package from Auto Enginuity direct with the GM Upgrade package and I believe the total was $296.00 the technicion you talk to is Jay and he seems very knowledgable about any problems you would encounter. The latest version of software from them allows resetting timing and most other functions from the Tech-II. Good software and good deal. You do need the GM specific Add-on. Clarke

Auto Tap

I finally purchased an OBDII setup made by Auto Tap (Model AT1 for GM). After installing the software I plugged it into the truck and turned the key to the ON position without starting the truck. I hit connect on the laptop and it immediately connected and pulled up my VIN number. After that I was
able to configure a virtual dashboard of gauges within 3 minutes of starting. I was also able to check the trouble codes (DTC codes) and any MIL light history. I then ran the trucks and made a few different configurations based on my current interests. All very easy and I didn't read any
instructions whatsoever.

I then used the device while working on a customer's 01 open top, and it performed perfectly again, showing the last codes registered in history, and also that there were no current codes in the system. We monitored the transmission temp to ensure it was at the proper level to check the fluid and then went through about 8 other system checks.

There is a graphing function that I haven't explored yet, but that will probably be later this week. You can also save configs for each VIN number so that when you have multiple cars or customers, you can keep the config and history for each one.

I bought the setup on Ebay from a private individual who never even opened the package for $130, retail IS $189, and the GM extended code package is another $99. So far I don't have a use for the extended codes as this pulled up very detailed GM specific codes already.


Different OBD Scanners:

I checked to see if the Mac scanner worked on my truck. It had a bit of trouble communicating with the computer at first, but that was probably due to my inexperience with the scanner (I have only used it one other time). After a bit of tinkering it worked no problem. I found it to be very easy to use and have some nice handy features built in to it like a code library, which you can use to look up any codes that the scanner gives you. I would say for the money its a nice unit and would be a helpful tool. Its also very simple to use, heck you could train a monkey to operate this thing.

Use this VIN: 1gchg35f4w1107715

Scan Guage

I've been using a digital monitor that plugs into the OBDII port under the dash. It will work on our trucks, 1996 and newer.

It reads what the sensors are telling our PCM. It will give up to 4 gauge readings at once. These include water temp, intake air temp, voltage, rpm, mph, plus about 6 other readings. Not all work on a diesel (ex. "ignition timing) and the unit can be used on both gasoline and

You can also view mpg, trip miles per gallon, gallons per hours, average fuel economy, average speed, etc.

Lastly you can view trouble codes and clear them if you wish. I've used this device on the last 3 vehicles I've bought during the test drives. The owners/dealers all wonder what the heck I'm plugging in and are just amazed at the amount of info available instantly. (Great scan for trouble codes on used vehicles before you buy the dang thing). Its only about 6"x3" so its sits on the dash nicely.

It doesn't matter what our gauges are reading, it's what the sensor is telling the computer thats important. This little device allows you to "see" what the computers basing all driving parameters on. I bought mine directly from the manufacturer, cost is about $120.00

I don't sell or have anything to do with the company other than love this tool.

Regarding your temps, my actual dash gauge show right at about 200 degrees, give or take a 1/6" on the face when warmed up. But the computer sees a difference from about 186 degrees to 198 degrees for that same gauge spread. It's so precise you can see exactly when the thermostats open for the first drive of the day.

You can research the scan gauge at www.scangauge.com

AutoScanner from Autozone

Reads and erases Diagnostic Trouble Codes (DTCs) and turns off check engine light. Retrieves all Generic OBD II trouble codes (P0), their definitions and pending codes. Costs around 120.00