Battery Voltage & J2534 Programming
How important is battery voltage when executing a J2534 programming event? In most situations, it can make the difference between a successful programming event and a bricked ECU. The OEMs use a variety of suppliers for their ECU hardware, and there a large variations, even within individual OEMs, on how the ECU communicates with any external test device (ETD). Battery voltage fluctuations, device activations and electrical noise can all affect how the data is transferred to the ECU during the programming event.
If you do not own a quality programming power supply and are performing any reprogramming functions (J2534 or OEM tool) you are engaging in very risky behavior. There are many companies that offer programming power supplies, including Midtronics, IOTA, Fronius, Ateq, Schumacher to name a few of the players. When you are shopping for a programming power supply there are several questions that you should ask yourself to help decide which features you will need. Here's a sample:
- What OEMs are you planning on performing programming events on? Most Domestic and Asian brands are happiest when programming voltage is in the 13.4V-13.6V DC range. FCA controllers will not even start a programming event if the software sees voltage at DLC pin 16 over 13.99V DC. Contrast that with most European OEMs that require programming voltages in the 14.0V-15.5V DC range. You will most likely need a unit that has a variable voltage to accommodate these variances.
- What is the amperage requirements of the chassis? The original programming power supplies were in the 50-60 amp range. Some modern platforms now require 75-110 amps during a programming event (like some F-chassis BMW)
- What types of batteries are being boosted? Many of the late model chassis are now using AGM batteries rather than flooded lead acid. How they get and maintain a charge is VERY different. Make sure the unit has accommodation for the different battery types.
Some closing thoughts:
Most of the programming applications provide system battery voltage (measured a DLC pin 16) at some point during the process. Pay close attention to what is being displayed. Nissan, as an example, provides battery voltage in the NERS application before you start but will abort the programming sequence at 5% if it sees any excess electrical noise. The software, however, does not tell you that is why it aborted. Even cell phone chargers plugged in to the accessory power port can trip this.
Great information. Thanks Bob
I have had several push button start vehicles (Ford Mustang in particular) that would power themselves down if the voltage was not maintained above 14.0v. To resolve this in a pinch we used a running car and a set of jumper cables. Not everyone is as prepared for programming as they should be.
Excellent addendum to this topic! The push-button start systems have added another thing to be aware of, mainly how to get the ignition into RUN and not time out when there is no other activity seen by the BCM. Here is a TSB from GM that discusses this. I think most OEMs do something similar.
We fasten the seat belt on BMW to keep the car awake. Will that work on GM?
I don’t think any GM is that smart. The BCM is normally looking at RKE inputs, door switches and a few other things to determine if the system should be powered down.
Our shop just experienced an issue with 2 separate 6T70 TCMs that were bricked due to suspect battery condition and an ineffective power supply.
To add a little more to the topic, most newer Audi's will shut some systems down if the voltage goes over 15 volts anytime you are charging them, not just during a programming event.
So, if you are trying to do diagnosis or something on a newer Audi and you have a battery charger hooked up that is going over 15 volts, then some things on the car won't work, like if you try to roll a window up or down. There won't be any warning lights or indicators, but if you do a whole vehicle scan, you will see overvoltage fault codes in several modules, and it only takes 15 volts for this to happen.
Excellent point. The European manufacturers pioneered load shedding strategies for both over-voltage and under-voltage conditions. The AGM batteries they are installing will boil over a certain threshold. Maybe someone from the battery business can fine tune this? I have seen documentation anywhere from 15.0v DC to 15.6v DC, which is a big spread in my opinion.
I have seen some Ford Super Duty trucks cycle the blower motor on/off repeatedly if the battery charger is used with the key on and the voltage goes to high as well.
Hi Bob, do you have a list of programming voltages, by OEM?
In the interest of “generalization”, here’s what I found over the last 15 years:
Domestic and Asian brands are happiest in the 13.4V-13.6V DC range.
Euro brands will often require over 14.0V DC, some upwards to 15.0V DC.
You will either need a programming power supply with variable voltage settings or get two units.
Minimum amperage is 55, 65-70 is better, Some Euro (like select F chassis BMW) require 90 amp.
Hello Bob, thank you.
Are you aware of any tool or device that can demand a change in voltage of a voltage stabilizer unit via a RS232 port?
Unlikely. RS232 is a very low amperage port. Do you have a specific use case in mind?
Sorry Bob, I did not explain clearly. I have a voltage maintainer here that has both DB9 and DB25 RS232 ports fitted to it. The voltage maintainer has a stated capacity of 12.49V to 15.23V, in 100=mV increments. It has a stated rated output of 120a. I was informed that the developing engineers use the RS232 port to drive the voltage up and down on demand, via a command through said RS232 port. My question to you is; are you aware of any scan tools / pass through devices that can request this function via a RS232 port?
Right, most of the higher end units have a serial connection to install updated firmware and/or make adjustments as you describe.
Bob, thank you.
This now becomes a lot clearer. Do you have a list of units that do, or could you name a particular unit that does?
not positive, but I think Midtronics and Fronius are two examples. Pretty sure their older models used RS232. Everything has migrated to USB like this:
Thank you Bob, I meant, which scan tools have this as an available output?