Brake Override Action Strategy
The subject vehicle is a 2013 Ford F53 Motorhome chassis – this was one of those big Class A motorhomes powered by the 6.8L V10.
The data for this case study is from a vehicle I looked at back in 2013 when I worked for the local Ford dealership (hence the low miles). Even back then, I was really good at saving data.
The customer’s complaint was intermittent low power. There were no DTCs stored in the PCM. I rode with the customer and was able to get a recording when it acted up.
From the beginning of the recording up to the -28 mark, notice that APP1 & APP2 follow APP and the vehicle had normal power.
Now notice from the -10 mark to about the 12 mark, the customer is pressing the accelerator pedal (indicated by APP1 & APP2), but APP is stuck at 13%. Looking at both TP PIDs and the MAF PID, you can tell the ETB is not opening. That was the low power condition the customer was experiencing.
What the customer was actually experiencing was the Brake Override Accelerator (BOA) strategy. Here’s some description of BOA:
In the event the accelerator pedal becomes entrapped, such as by an object lodging the pedal, the brake over accelerator feature will reduce engine power when the brake pedal is applied.
Operators that rest a foot on the brake pedal when also applying the accelerator pedal may activate the brake over accelerator feature. The brake activation is detected by the PCM from the electrical brake switch. In addition to brake over accelerator comments, the customer may bring the vehicle in for repair to address concerns such as a hesitation/stumble or a lack/loss of power. In the event of a hesitation/stumble or a of lack/loss of power concern, carry out normal vehicle diagnostics for the appropriate symptom code. If the brake over accelerator feature is suspect, the BRKOVR_ACTION, BRKOVRD_POSS and DIST_BRKOVRD PIDs will display a brake over accelerator event occurred.
In the event the brake over accelerator feature is suspected as the cause of the customer concern, explain to the customer the details of the override system as described above. Additionally, make sure the customer is aware that resting a foot on the brake pedal while driving may cause the activation of this feature. This also results in activation of the brake lights on the vehicle while driving. For additional information, refer to the Owners Literature.
- BRKOVR_ACTION: Number of drive cycles where Brake Override Accelerator Action Occurred
- BRKOVRD_POSS: Number of drive cycles where Brake Override Accelerator Action Possible
Notice, during the low power event, both BOO1 & BOO2 are “On” and the BRKOVR_ACTION, BRKOVRD_POSS PIDs show high numbers. The accelerator pedal and brake pedal were fairly close together on this vehicle. Turns out, the customer was accidentally pressing the brake pedal while he was trying to accelerate. At first, he didn’t understand or believe what I was telling him. I had to show him the data.
This is just one example of where a normal computer strategy was perceived as a problem. What other examples have you experienced?
This is going way back and this story is related to a computer strategy that actually resulted in a real problem that plagued a ton of vehicles built back in the late 80's, early 90's.
Problem: GM 454 Big Block Exhaust Manifolds, breaking studs, leaking gaskets, cracked manifolds etc. I commonly saw these being replaced only to have the issue reoccur. This was especially true for those towing boats and other heavy items. The main cause was due to the "Power Enrichment Delay" set within the PCM calibration. After performing a ton of research on this and actually getting a look inside the calibration, I discovered the truth. There was a 60 second delay from the time TP% was >80% before going into P.E. mode. This left the AFR @ stoich with a terribly detuned spark table. Late spark and a lean exhaust resulted in the manifold glowing red hot. Now there were a few by-pass items within the calibration that would kill the 60 second timer (such as >4800 RPM) but that was still too late. I did witness many customers who had this problem rectified by purchasing an E.O. performance PROM. We even ran many of these on the dyno (before and after) and observed increased power and a noticeable reduction in manifold color change. The glowing red exhaust was no more and customers were happy again. 🤓
Btw, we saw that the VIN decoder didn’t work for you on your post and that’s because that vehicle is in the medium duty class which our current database doesn’t support. We intend to rectify this soon.
Thanks for sharing.
Interesting - I wonder how many people attributed that failure to poor quality parts.
I did notice the VIN decoder didn't work for that VIN. I also tried to type in the symptoms in the Symptoms box, but anything I typed would go away when I tabbed to the next box.
Thanks for the reply!
Wow, that is some great info that I just learned! It had been a couple of years since I worked on one of these, but a newer one (1997) was in last week. Of course, I checked the manifolds and ignition wires, and nothing was broken of melted! I was always amazed at how the older one roasted wires and broke manifolds, but I never knew that their fuel strategy had anything to do with it.
I likely will never work on another one, but I still like to know this info. ;)