What the hell is a Misfire Correction Factor and why should I care? Exactly my thought as well – and as soon as your DB9’s battery goes dead or is disconnected for service work, you car will forget this critical engine tuning data and then you’ll care.
What makes this a bit more confusing is that the issue is described under many names, but all referring to the same thing:
- Misfire Correction Factors
- Coast down procedure
- Adaptive Learning Procedure
- Flywheel Learning Procedure
How Aston Martin Describes it
The Engine and Transmission Control Modules use an adaptive learning process to improve performance by compensating for manufacturing tolerances in the engine and transmission. Benefits include:
- More accurate misfire detection
- Improved engine emissions
- Smoother gear shifts
The adaptive learning procedures are required when either the Powertrain Control Module (PCM) or the Transmission Control Module (TCM) have been reprogrammed or have lost their ‘Keep Alive Memory’.
The following procedures will therefore enable the Control Modules to ‘relearn’ the relevant data if lost following service work during which keep alive power that has been lost. The original data would also be erased from the controller memory if any Module has been ‘reflashed’.
A Technical Description
Grant Neal writes about it this way in his excellent book “The Definitive Guide to the new Gaydon Era Aston Martin”:
A new engine management system (Spanish Oak) was also introduced, unveiling another new advanced feature called a ‘neural net misfire detection system’. Ford had been working to bring this JPL NASA developed technology to their cars since 1998 and the DB9 was to feature the fist on-board neural network in an engine control module. Craig Stephens, manager of Research and Advanced Powertrain Controls at the time of the 9’s launch (2004) provides further information in his official press release: “The DB9 was quite a challenge because of its V-12. The engine frequency of firing events is so high that the legislative requirements for the misfire detection could not be met with conventional computing resource. Neural networks offered us a whole new paradigm for computing and the potential for a misfire detection system that would be fully capable of meeting every detail of the regulation.” He continues, “Unlike traditional computer system that need to be programmed for each step, neural networks are programs modelled on the way human brains learn and adapt. The DB9’s module keeps tabs on engine combustion performance with a sophisticated software program that compares actual engine performance to design specifications. The designers build a critical threshold number of misfires into the system. Once the neural network detects the critical number, the Check Engine light is triggered and the misfiring cylinder is shut down to avoid damage such as a melted catalytic converter. We now have the most complex vehicle application of a neural network in the world.”
There is also an excellent article online published by Ford that goes further with explaining what Craig Stephen’s was describing above. Worth a quick read if you like to understand how cool the DB9 is.
How do you know you need to relearn the Misfire Correction Factors?
It was during my recent trip to my local dealer to have my engine software updated I learned from Tim (a certified Aston Martin Master Technician) that my car currently had NO misfire correction factors and that the learning procedure must not have been done after some previous service by the DPO (Damn Previous Owner).
Tim also explained that the engine would have been operating on a very rudimentary set of parameters while awaiting someone to tune it. He encouraged me to follow the process below whenever I could manage it.
The Misfire Correction Factors can be accessed by a service technician using the AMDS (Aston Martin Dealer System) computer linked to the car. If the Dealer is going to disconnect the battery for service work they backup the correction factors, and then restore them afterwards. Great, as long as you have a $15,000 AMDS handy.
The sad truth of it is that us DIY guys have no idea if the engine has no codes and is running in default mode, or if it has codes. Normally there is no way to tell without using the AMDS system. [UPDATED March 27, 2016] I’ve learned how to determine if the Misfire Correction Profile IS or IS NOT Learned using my Autel MaxiDiag MD802 OBDII Code Reader. You can check out my blog post on using an OBDII code reader and how to read the Misfire Status in my other post ‘Getting More information with your OBDII Reader’ for more information on this.
When do you need to relearn the Misfire Correction Factors?
As noted in my other blog posts on Seat Calibration and Window Calibration, the engine PCM’s also use the type of storage memory (‘Keep Alive Memory’) that instantly erases if power is removed even for a moment. So if you have a low battery, dead battery or service event that causes the power to the PCM to be interrupted, the calibration will be lost and the factors will need to be relearned.
This could happen if your Dealer reflashes (updates) the PCM software.
Another condition in which you will want them to be relearned is if you do service work that replaces the Coil Packs or Spark Plugs. Since these are the an integral part of the engine ignition system that the Misfire Correction Factors are designed to optimize, if you change them you need to re-calibrate to get the full benefit of your hard work.
The short answer is that if you’ve had a dead battery or disconnected your battery for any reason, you can be assured the memory is lost and you should do this procedure.
How to relearn the Misfire Correction Factors
Surprisingly I’ve been unable to find any documentation of the procedure in the Official Aston Martin Workshop Manual. The need is foreshadowed, but the process is not explained:
“After connecting the battery, the radio preset stations and the door window controllers will require to be reset (Adaptive learning data in the PCMs and TCU (Auto transmission) modules will require to be re-learned by driving the vehicle for some miles in a range of driving conditions), drivability may be slightly compromised until the vehicle systems have completed their adaptive learning routines again.”
Aston Martin released Service Bulletin SB148 “Flywheel and Gearshift Learning Procedures” in November 2004 as the issue is so common. You can read it here.
I’ve also received inspiration for this article from a forum post over at 6Speed as well as others.
The process is simple, but the hardest part is finding long enough stretch of open road to perform the steps. Essentially you get the car up to speed then coast for a long while several times in a row, and the ECU is closely monitoring how the engine ignition is working during the zero throttle coasting. Don’t ask me how, but it does.
- Be safe – at times you’ll be coasting along an Interstate Highway at just 20 m.p.h. so plan when to do this so you aren’t out in traffic. I tackled it at 6am on a Sunday morning.
- The car needs to be up to normal operating temperature. Be sure to drive a few miles before you start the process.
- Turn off the Air Conditioning. It will NOT re-calibrate if you have the A/C on. I turned my climate control know to the OFF position entirely.
- In a Touchtronic (automatic) car, make sure you are NOT in Sport mode, or paddle shifting. Just have the car in normal Drive (D) mode. In a Standard (manual shift) car you can just do the procedure in 6th gear.
- On a long, clear, flat open stretch of road accelerate normally to 70 m.p.h. and cruise along in 6th gear then let off the throttle completely and coast down to 20 m.p.h. without touching the brake or the throttle. If you do, this aborts the learning process and you need to start over.
- When the car reaches 20 m.p.h. accelerate normally again to 70 m.p.h. and repeat step 5. Remember you can’t use the brakes AT ALL during this procedure.
- Do this coast down procedure a total of 5 times [see my update on this below].
The really unsatisfying part is you will have no indication that its worked (or not). Blind faith. The next time you are at the dealer you can ask them to check (and save the codes to the AMDS if it did work). [See my update on this below]
[UPDATED March 27, 2016] I’ve learned how to determine if the Misfire Correction Profile IS or IS NOT Learned using my Autel MaxiDiag MD802 OBDII Code Reader. You can check out my blog post on using an OBDII code reader for more information on this. But, after I followed the coast down procedure above and hooked up my code reader and looked at the Live Data indicator for MP_LRN(Misfire Profile Correction Learned), the value was set to YES. See the photo.
My mechanic Tim told me the official factory procedure describes 70 to 40 just 3 times, but his experience has shown it might need a little longer time coasting and a few more tries, so he suggested 70 to 20 for 5 times. If I’m going to do it, I just want it to be done.
[Updated January 17, 2017]
I had to relearn the profiles on my car again recently since I changed my Coil Packs and Spark Plugs. When I did it this time I decided I would have my OBDII Code Reader hooked up ‘live’ within the car and watch the Live Data field (noted in the update below) and see when it actually decided the profile was learned during the procedure.
I followed the learning procedure, and to my surprise it was learned after just ONE coast down from 70 to 20 mph. I saw the live data value change from NO to YES. No need to do four more coast downs [Sweet, since this needs a really large gap in traffic]. I suspect this might vary on the condition of your engine and what the computer thinks, but it could also be that they are just being super conservative and suggesting to do it multiple times since you normally wouldn’t have an OBDII reader attached giving you the live play-by-play. So, if you have one, I’d say modify the procedure to watch your live data and do the coast downs until the value changes to Yes. If you don’t have a reader, then I would say still do the five coast downs to be sure you get it done.
I’ve created a simple video of me doing the procedure if you’d like to see me out driving at 6am in the dark on Interstate 5 north of Sacramento, desperately in search of a long and clear enough stretch of open flat road. It seems like forever to coast down. Have a look…