Other Articles - October/November - 2015

Pass-Through Programming: Taking Matters Into Your Own Hands

As today’s vehicles become more and more complex, there’s more pressure to be aware of how these vehicles operate, how they’re controlled, and what can go wrong to cause customer complaints. Since the introduction of computers, we’ve watched the complexity of control systems explode.

Now you need to pay attention to the computer network that’s in charge of making everything work together, to make sure it isn’t causing the problem you’re dealing with. With that in mind, it’s time to add programming to your laundry list of checks, even if you don’t have the ability or desire to program. So let’s look into the world of programming vehicle computers.

At first, ECMs and TCMs were built specific to each vehicle, with non-interchangeable hardware that contained the programming to run the vehicle. They usually had a basic firmware program embedded. Then a programmable microchip, called a ROM (read-only memory), was added to calibrate the computer to each specific engine and transmission.

Later they replaced the ROM with an EEPROM (electronically erasable programmable read-only memory) chip, which allowed for fewer hardware changes and greater flexibility. EEPROMs contain the programming, and can be erased and reprogrammed or updated as necessary. EEPROMs often fail during programming because of internal hardware failures.

The latest generation of computers allows for programming from the firmware to the software level. They offer vehicle manufacturers more options for suppliers to produce more cost-effective components and greater application flexibility.

With all the advances in automotive computer technology, a need arose to develop a standard for computer architecture and communication. The SAE (Society of Automotive Engineers) developed the J2534 standard.

This standard was adopted through extensive cooperation between the automakers and the aftermarket, to create a worldwide communication and architecture platform. This platform offers everyone access to streaming data and programming capability, through a cost-effective, universal interface tool.

The J2534 standard also mandated that automakers provide downloadable software to the aftermarket from a technical support web site. Now there are a number of companies that produce J2534 compliant interfaces, also known as pass-through devices. These devices range from around $1500 up to tens of thousands of dollars. With such a huge price range, it’s reasonable to assume that all passthrough devices aren’t created equal.

To provide as much real time information as possible without any bias, we’ll look at factory level information from the automakers’ web sites regarding the compatibility of aftermarket pass-through devices. First let’s examine the equipment you’ll need to start programming.


Purchasing a pass-through device is only part of the picture. A computer or scan tool, an internet connection, cables, and a web site access subscription will round off the package (figure 1).

The computer needs adequate processor speed, hard drive storage, and compatible drivers as designated by the manufacturer’s web site. This is often overlooked and causes download and upload freezes and failures.

Before purchasing a computer, log on to the web sites for the manufacturers of the vehicles you’ll want to program, and check the system requirements (figure 2). It’s extremely important that you meet their minimum requirements; even better if you exceed them.

The processor type and speed are critical. If you use an aftermarket scan tool, keep in mind that the processor speed and hard drive storage capacity may become obsolete and won’t be able to be updated based on future changes by the manufacturer. Of course, OEM tools work the best (figure 3).

Next, your internet connection is critical. In direct pass through programming, a poor, slow internet connection will cause programming failures. High speed, fiber optic connections work best. And Wi-Fi is a definite no-no, unless you are downloading the program onto your computer first. It is recommend ed to always connect your computer directly to your modem.

The quality and fit of the cables are important. The cables between the pass-through device and the computer, and the one between the pass-through and the vehicle, are usually included with the device. Make sure all connectors fit securely.

Purchase a high quality cable for your internet connection, too. Sometimes the one from your internet provider is substandard. Make sure that locking tabs secure properly where applicable.

It’s important to keep the equipment and cables from moving while programming. Movement may generate signal noise and cause errors. If you’re using a laptop computer, make sure your battery is fully charged or use your AC charge cord. And never switch between battery and AC power while programming.

Finally, your choice of a pass through device will depend on the vehicles you want to focus on. Some manufacturer’s web sites include a list of pass-through devices that were tested by the OEM and approved for compatibility.

Buyer beware! Even though the J2534 standard implies that all aftermarket pass-through devices will work with all makes, some manufacturers favor certain aftermarket units. It’s primarily a result of engineers and support staff working with the manufacturer to develop and support the OEM tool. It is best to look for a pass through device that has real time technical support as well. Research thoroughly before you purchase.


With all components in place, you’re ready to access the manufacturer’s web site to download the software for your application. Always look through the manufacturer’s web site to see what’s actually available for pass-through programming.

Most sites only make software updates available for the PCM and TCM. Other modules are only programmable through the dealer. Most firmware is proprietary and isn’t available for download or programming.

Before purchasing a subscription, make sure you’re accessing the correct technical resource from the manufacturer to obtain downloadable programming. Some manufacturers provide their programming on a CD. Again, read what’s available so you don’t waste time and money on a subscription that provides no useful programming resources.

Once you’ve verified that programming downloads are available, you can select the appropriate subscription and make your purchase.

There may be other perks that come with your subscription. Usually the manufacturer’s web site will allow limited access to factory manuals and publications for download. Look through their database whenever it’s available for any bulletins that could affect the vehicle you’re working on.


Once your hardware and software are set, you need to make sure the vehicle’s ready. First, make sure the computer can be programmed. It sounds obvious, but not all of them are.

Make sure you can communicate with the module or modules you intend to program. If you can’t communicate with the modules with a scan tool, you must find out why and fix that issue first. Set your scan tool to OBD II global, and record and correct all communication codes. Test the module for good power and ground, and try to determine whether you have a bad module before you attempt to program it.

After verifying that you can communicate with the module, make sure vehicle battery voltage is good and stable. Connect a trickle charger to make sure battery voltage remains above 12 volts. In some applications, a clean power source is necessary (figure 4). Remember, the vehicle will be sitting with the key on, engine off for several minutes.

Make sure all accessories are off. Disable automatic leveling air suspension, and disable daytime running lights. Make sure that the vehicle is cool enough that the radiator cooling fans don’t turn on.

Finally, check your computer. Make sure your wireless communications are disabled, including Wi-Fi and Bluetooth devices. Securely fasten your cable from the pass-through device to the vehicle’s OBDII connector.

Place your laptop or scan tool where it won’t be moved or disturbed. If you’re using a desktop computer, route the cables so that no one’s likely to trip or run over them.


Access the manufacturer’s web site, which should direct you step by step through the process. The process will allow for removing the old software and writing the new software. Sometimes it’ll include an overwrite, which adds programming to the existing software.

It’s important to monitor the programming process and follow all prompts. Read twice and click once! Once programming is complete, you’ll see a verification screen. Never interrupt the programming process unless directed to do so: That can damage the module and render it useless.


Of course, problems may arise when programming. Most issues are from not paying attention to the details. From hardware inadequacies to fundamental user errors, the most common issue is vehicle battery voltage instability during programming.

If you follow the instructions we’ve covered, you should avoid programming freezes, failures, and non-responsive modules.

If your voltages remained in the safe zone but you still had a programming failure, simply start the process again. Some modules are stubborn. They may take three or four attempts. Be persistent. You may need to contact the manufacturer if a problem persists.

Programming is here to stay. If you plan on remaining in this industry, you’ll need a plan for dealing with programming. If you bury your head in the sand and pretend it doesn’t exist, you’ll throw away diagnostic time and money.

Including programming in your total service package, from diagnosis to delivery, is the smart way to handle today’s market. Whether you contract programming to the dealership or mobile technician, or take it on yourself, understanding programming puts you in the driver’s seat.