USA Cars (GM, Ford, Chrysler) PCM Flash Reprogramming Instruction

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USA Cars (GM, Ford, Chrysler) PCM Flash Reprogramming Instruction

This is a how-to’ of American cars PCM flash reprogramming incl. GM, Ford, Chrysler.

Topics are discussed here like:

  1. PCM Programming is Nothing New
  2. Why Reprogram PCM?
  3. Who Can Do PCM Reflashes
  4. PCM Reflashing Requirements
  5. GM Flash Updates
  6. Ford Flash Procedure
  7. Chrysler Flash Procedure
  8. WARNING! PCM Flashing Is Risky


in detail…


Flash reprogramming PCMs is NOT for the feint of heart. First, you have to have a scan tool or J2534 device that can reprogram your vehicle’s computer. Then you have to go to the vehicle manufacturer’s service information website, pay an access fee and find the correct update for your vehicle. Then you have to download their interface software for your laptop so it can handle the vehicle download,. Once that has been installed on your laptop, you can download and transfer the new PCM or other module programming to the J2534 interface tool or scan tool. from there, the software is transferred into the vehicle via the DLC connector to update the PCM or other modules.

PCM flash reprogramming has become common as vehicle modules get smarter and more complex. General Motors estimates that they have released flash updates for as many as 70% of 1995 and newer GM vehicles.

Amercian Cars PCM Flash Reprogramming 1

Basic steps of flash reprogramming a vehicle computer.

Part 1: PCM Programming is Nothing New

Flash reprogrammable PCMs have been used in vehicles since the 1990s. The first such application was the 1990 Geo Storm. Previously, Program Read Only Memory (PROM) chips held all of the PCMs vital calibration information and operating instructions. GM pioneered the replaceable PROM chip as a way of programming PCMs to fit a wide range of GM makes and models. A replaceable PROM chip also meant the PCM could be “retuned” if necessary to correct certain kinds of emissions or driveability problems. It also meant that if a bug was later discovered in the original factory programming, it could be corrected in the field by simply replacing the original PROM with an updated corrected PROM (a tactic GM has successfully used over the years to fix many factory flaws). Performance enthusiasts also liked replaceable PROMs because the chip could be replaced with one that provided more spark advance, fuel enrichment, a higher rev limit, etc., to squeeze more power out of the engine.

But replaceable PROMS had a serious drawback: there were too many of them! Every model year and every running change meant another PROM had to be created. Every field fix or recall for an emissions or driveability problem created more part numbers to keep track of. We are talking thousands of different PROMS. The General Motors PROM Identification manual that OTC used to provide with their Monitor scan tool and Pathfinder software contained more than 362 pages of GM PROM numbers!

Enter the flash reprogrammable EEPROM (Electronically Erasable Program Read Only Memory) chip. PCMs built with EEPROM chips can be reprogrammed in a matter of minutes without having to remove the PCM or replace a single chip. It is all done digitally with the proper access codes and input data.

Following the Geo Storm, GM began phasing in PCMs with flash reprogrammable chips in a variety of cars and trucks. By 1995, most GM models had the flash reprogrammable PCMs. Ford and Chrysler were also doing the same thing as OBD II arrived on all cars and light trucks in model year 1996. Today, virtually all PCMs have reprogramming capabilities as do many other onboard control modules (ABS, air bags, climate control, body controller, etc.). This allows changes and upgrades to be made as needed.


Part 2: Why Reprogram PCM?

PCMs may need to be reprogrammed for several reasons. One is to fix factory bugs. Every time Bill Gates rushes yet another version of Windows to market to perpetuate the Microsoft revenue stream, it always turns out to have bugs and security holes that were somehow missed but must be fixed by downloading and installing the latest Windows “service pack.” It’s a never-ending cycle of upgrades and patches. Fortunately, it is not that bad yet with automotive PCMs, but it has become a crutch for automakers who rush products to market that aren’t quite ready. This philosophy of “build it now and fix it later” creates a lot of unnecessary recalls, but at least it gives technicians a way to fix factory mistakes without having to replace any parts.

A reflash may also be required if the factory settings for the OBD II self-diagnostics turn out to be overly sensitive – especially after a few years of operation. The same goes for driveability. What works fine in a brand new car many not work so great after 50,000 or 100,000 miles of real-world driving. Changing the fuel enrichment curve, spark timing or some emissions control function slightly may be necessary to eliminate a hesitation, spark knock or other condition that develops over time.

For example, on certain GM vehicles the Check Engine light comes on and sets a code P1406 that indicates a fault in the position of the exhaust gas recirculation (EGR) valve. Cleaning or replacing the EGR valve and clearing the code does not fix the vehicle because the code usually returns. The real problem is the OBD II programming in the PCM. When the PCM commands the EGR valve to open to check its operation, it isn’t allowing enough time for the valve to respond. A brand new valve takes only about 50 milliseconds to open but an older valve may take up to 350 milliseconds or longer – which is not long enough to cause a real NOx emissions failure but is long enough to trip a fault code. The fix in this instance is to reflash the PCM with new instructions that allow more time for the EGR valve to respond.


Another example are rich codes that may appear on some late-model GM vehicles. The problem here is that the original OBD II self-diagnostic programming does not allow enough leeway for changes in intake vacuum that occur as the engine ages. After 60,000 miles, intake vacuum isn’t as high as in a new engine, which can create a rich fuel condition. The cure is to flash reprogram the PCM to compensate for the drop in vacuum.

When vehicle manufacturers calibrate the onboard diagnostics to meet federal emissions standards, they have to draw the line somewhere as to what operating conditions might cause emissions to exceed federal limits 1.5 times. That is the threshold where a fault code must be set and the Check Engine light must come on. It doesn’t mean emissions really are over the limit, but it is possible based on laboratory dyno testing and field experience. Depending on the application, the vehicle manufacturer may even set the limit a little lower just to be safe because the last thing any OEM wants is an expensive emissions recall.

The best advice when confronted with a troublesome code that keeps coming back or seems to set for no apparent reason is to check for any technical service bulletins that may have been published. Chances are it might be a programming issue that requires a reflash to fix.

Something else to keep in mind with respect to many late-model flash reprogrammable PCMs: if you replace the PCM for any reason, the replacement unit may have to be reflashed before it will start the engine! Some modules are plug-and-play, and are preprogrammed by the dealer or aftermarket parts supplier so they can be installed ready-to-go. But many need vehicle specific calibration information to run properly. This may require downloading old calibration information from the original PCM (if possible) and reloading it into the replacement PCM, or getting updated calibration information from the vehicle manufacturer to install in the new module.

If you are buying a reman PCM from an aftermarket supplier, they may be able to program it for you. The information they need to do this includes your year, make and model of vehicle, engine size, vehicle identification number (VIN), the type of transmission (manual or automatic), the emissions type (federal certification or California), and other options that may affect the calibration of the PCM. Your other option is to have a car dealer or repair shop reflash the computer, or attempt it yourself.

Part 3: Who Can Do PCM Reflashes

Historically, car dealers have been the only ones who had access to the tools and software needed to reflash PCMs. Thanks to the passing of Senate Bill 1146 in September 2000, vehicle manufacturers must now make this technology available to independent repair shops and individuals at reasonable cost.

Starting in 2004, flash reprogramming procedures also had to conform to SAE J2534 standards that allow the use of aftermarket scan tools or similar pass-through devices.


Part 4: PCM Reflashing Requirements

Reflashing PCMs requires three things: a scan tool or J2534 pass-through device that is flash capable, a Windows laptop computer (Most require Windows 7 but some older applications may require Windows XP) with an internet connection for downloading the flash software from the vehicle manufacturer website, and a subscription to the manufacturer’s database so you can access the software for the laptop and the vehicle. Other items that are needed include a cable to connect the laptop to the scan tool or J2534 pass-through device, and a cable to connect the scan tool or J2534 pass-through device to the OBD II connector on the vehicle.

You will also need a battery power supply source or charger that can maintain a steady constant voltage to the vehicle during the reflash procedure. You do NOT want any voltage drops for fluctuations during the reflash because it may screw up the programming of the PCM.

For older GM applications, you can use a Tech 2 scan tool or Vetronix scan tool or other aftermarket J2534 pass thru tool.

For older Ford applications, you can use a Ford New Generation Star (NGS) scan tool, or an IDS scan tool or aftermarket J2534 pass thru tool for newer Ford vehicles.

For Chrysler applications, you need a Diagnostic and Reprogramming Tool (DART) or a Chrysler DRB III scan tool. These tools are available from OTC Div of SPX Corp.


Aftermarket reprogramming tools can also be used to reflash Chrysler PCMs, but Chrysler says they have encountered some problems with certain J2534 devices. This involves all their powertrain SCI engine computers from 1996 to 2004, and some PCMs from 2005. To avoid such problems, Chrysler recommends using the J2534 Vehiclebox tool device while performing SCI protocol-based reprogramming using their J2534 flash application.

Before you begin a reflash on a Chrysler PCM, the programming application needs to establish successful communication with the vehicle computer. This can be accomplished by doing the following steps:

Temporarily disconnect all aftermarket alarms, remote start systems, audio systems to prevent electronic interference.
Check vehicle wiring for any obvious defects.
Use the recommended J2534 device.
For technicians using a factory service tool, Chrysler’s wiTECH is capable of programming SCI computers in 2004 and newer vehicles. For 2003 and older vehicles, the DRB III scan tool should be used.

For import applications, you need whatever factory scan tool the dealer uses, an aftermarket scan tool with reflash capabilities for that vehicle, or a J2534 pass-through device that will work on the vehicle.

Yearly and monthly access fees to OEM databases tend to be very pricey, but one-day or short-term access fees are typically available for $20 to $25.

Some vehicle manufacturers provide their flash updates on a CD once you pay their subscription fee, but most provide the software update as a download over the internet after you pay their fee. The download goes into your laptop computer. In some cases, the software must then be copied to a flash card which is then plugged into a scan tool or J2534 device for installation into the vehicle. In other cases, the software is fed through a cable or wireless connection to the J2534 device so it can be installed in the vehicle.


If the software download is feeding through an internet connection into the J2534 tool as it is being installed, you have to maintain the internet connection without interruption until the installation has been completed. If you lose the internet connection, you will have to start the installation all over again — and hopefully it will work. Losing the connection part way through an installation may royally screw up the PCM!

The flash procedure can takes from a few minutes up to an hour depending on the file size of the software you are installing. The newer and more complex the vehicle, the longer it typically takes to flash the PCM.


Part 5: GM Flash Updates

On GM vehicles, a list of flash updates that are available can be found on GM’s Vehicle PCM Calibration Information website at

The actual reprogramming procedure for a typical GM vehicle goes as follows:

  1. Check the calibration history of the vehicle — Go to the GM web page at to see what the latest vehicle calibration is for your car by entering the vehicle VIN number. If the PCM programming has been updated, the most recent calibration will be listed on the website. You can’t download the new calibration software from the website, however. You must first purchase a TIS subscription from GM, and then GM will mail you the calibration software on a CD. The software can then be copied from the CD through your PC to a flash card for the Tech 2 scan tool.
  2. Connect your PC to the Tech 2 scan tool with a RS232 cable pass-through device.
  3. Before you start the procedure, make sure the battery is fully charged. You do NOT want any loss of voltage during the procedure as this can really screw things up! GM does NOT approve using a battery charger, unless it is a GM-approved Midtronics charger (which delivers very consistent voltage with no fluctuations). On some vehicles, removing the fuses for the fan relays, fuel pump or other modules may be required to prevent these devices from turning on during the procedure.
  4. Start the GM recalibration software program on your PC (which you have to purchase from GM, along with the update CDs) and enter the vehicle application information (year, make, model, etc.).
  5. Connect the Tech 2 scan tool to the diagnostic connector on the vehicle (located under the dash near the steering column).
  6. Switch the Tech 2 scan tool on and wait for the Start screen.
  7. Validate the vehicle VIN number.
  8. Choose the operating system, engine, fuel system, speedometer or transmission.
  9. Select “normal reprogramming” or “VCI” (special modifications).
  10. Choose the update bulletin/recalibration number from the menu.
  11. Start the transfer of data. As the software is loaded, you will see a progress bar. The reprogramming procedure may take a new minutes to 30 minutes or more depending on the file size, and can be done with the computer in or out of the vehicle. The PC screen will display a blue progress bar as the software is uploading to the vehicle.

Note: The GM setup will NOT allow the same calibration to be reinstalled over itself. Only an updated calibration can be loaded into the vehicle computer. There is no going back to an earlier version.

  1. When the software has finished loading, the message “PROGRAMMING COMPLETE” will appear.
  2. Turn the ignition OFF, then disconnect the scan tool. Depending on the application, it may be necessary to run one or more “relearn” procedures before the PCM will function properly. Most GM PCMs require a “CASE” relearn so the PCM can learn the relative positions between the crankshaft and camshaft sensors. If you don’t do the CASE relearn, the Check Engine Light will come on and there will be a code P1336.


Part 6: Ford Flash Procedure

With Ford vehicles, a somewhat different approach is used. First, you need the vehicle calibration ID number. This can be found on a sticker somewhere in the engine compartment. Next, you have to figure out if there is a newer calibration available. This requires going to the website, selecting “Quick Guides” on the left side of the screen. On the next menu page that appears, scroll down to the link for “Latest Calibration Information.” The next screen says “Search Calibration by Vehicle, Model Year and Engine.” Enter your vehicle model, year and engine information, and click Submit. The next screen will list all of the possible calibrations by PCM part number. Find the part number that matches your PCM and that’s the latest calibration you need.

To get the actual calibration download, click on the “Reprogramming & Initialization” link at the left. You then have to buy a one-day subscription before you can download the software to your PC that is necessary to do the reflash. You will also need a J-2534 pass thru tool to do the reflash.

With Ford, the calibration software that will go into the car is not stored on the PC. The software that you downloaded only facilitates the transfer of the new calibration from Ford into the car. In other words, it is a “live” procedure that requires a continuous unbroken internet connection until it has finished.

Part 7: Chrysler Flash Procedure

Chrysler’s flash procedure is sort of a cross between GM and Ford’s procedures. First you go to the website and download their “benchtop Programmer” software to your PC. Then you download a huge pdf file (“J2534 Flash Availability”) that lists all Chrysler PCMs and their software updates. Chrysler uses vehicle body codes to identify the PCM in addition to the VIN, and you need to use a scan tool to get the module ID from the vehicle. If the vehicle needs a update, you go back to the Chrysler website, pay their access fee, and download the new software to your PC. Then you transfer the software from the PC to a scan tool or J-2534 pass-through tool to install it in the vehicle.

Also note, many Chrysler PCMs require a re-initialization procedure after a flash.

Here is a sample of the flash reprogram procedure a Chrysler dealer would use. This one happens to be for a recall Chrysler issued for 1999 California Dodge Ram Pickups and Vans with 5.9L engine (“Z” engine code in the 8th VIN position), automatic transmission and California emissions control system (code NAE). The OBD II catalyst monitor on these vehicles may not detect a catalyst failure so the PCM programming had to be revised to comply with California regulations.

The dealer accesses the latest software through the modem connection in the Mopar Diagnostic System, and feeds it through the DRB III scan tool into the vehicle’s PCM via the OBD II connector. The process begins by turning the ignition key on (engine off) and allowing the scan tool to “auto connect” with the PCM. Once the lines of communication are open, the VIN is displayed on the scan tool. The technician can now press the “OK” button to proceed with the reflash procedure.

The first thing he does is select “Read Part Numbers From Vehicle” and click “Show Updates” on the MDS2. If somebody has already reflashed the PCM, the screen will say “Part number is up to date and does not require any new updates.” The software number should be compared to the latest version to verify the numbers match just the same. If the PCM has not yet been updated, the technician clicks OK, selects the new software part number and clicks “Update Controller Software.” From that point on, the process is automatic – but there is a hitch. During the flash reprogramming procedure, the PCM loses communication with other modules on the vehicle that may set a number of “false” trouble codes for the transmission module, ABS module, body control module, etc. This does not indicate a problem and the codes can be erased after the flash reprogramming procedure has been completed. The technician is also supposed to attach a label to the PCM with the reflash part number and date indicating the PCM has been reflashed.


Part 8: WARNING! PCM Flashing Is Not Without Risk
So what happens if something goes wrong during a reflash procedure? Anyone who has ever experienced a crash while installing new software on a PC knows it can cause real problems. In some cases, the PCM may be so scrambled that it will not accept a reflash, which means you get to buy a new PCM!

Chrysler issued a TSB (18-32-98) that deals with how to recover from a flash reprogramming failure.

The bulletin says, “Occasionally a flash update procedure may not complete properly and/or the diagnostic equipment may lock up during the procedure.” Common causes of flash errors include poor cable connections between the PC, scan tool and vehicle, loss of power to the diagnostic equipment while the flash procedure is underway, turning off the vehicle ignition switch before the flash procedure is complete, unfamiliarity with the procedure (pushing the wrong buttons), or low vehicle battery voltage.

If the process crashes, recheck all the cable connections to assure good communications and reinitialize the flash procedure. In other words, if at first you don’t succeed, try, try again. On the Chrysler applications, you may also have to identify which type of controller is on the vehicle (SBEC2, SBEC3, JTEC 96-98, JTEC+ 99, etc.) to get the system to accept the new programming. If you get an error message again, you probably selected the wrong controller type (try again!).

Doing your own flash reprogramming is not without risk. Any number of things can go wrong during the installation process which may result in an incomplete update or a frozen PCM. The worst case is that you can’t recover the PCM and have to replace it. Out advice is to leave PCM updates to a knowledgeable professional. If your vehicle needs a flash update, take it to the car dealer or a qualified repair shop and let them do the update.


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