"Engine Malfunction" on radio for 2012 Fiesta S sedan

[dragonfly0201]

I have the wrench in my dash, and the 'engine malfunction service now' in the radio when I start my car. I have run my own OBD II code reader, gone to AutoZone and neither code readers picked up ANY codes...
I have Forscan and ran it, and it gave me a P0504 code, brake switch a/b correlation code. My question is: WHAT is causing this? I bought my car last month and it had the wrench in the dash when I bought it. It runs just fine. 5 speed transmission. 141k miles. There are 2 switches on my brake pedal. A black one and a blue/white one. Should I replace them both? Or is only one the cause of this wrench and engine malfunction service now notification?

 

[econoboxrocks]

The wrench means you're due for an oil change. I'm guessing that you aren't, but it needs to be reset.

 

[dragonfly0201]

I did an oil change after I bought the car. I attempted that reset and it did nothing to get rid of the wrench light in my dash.
I also have 'engine malfunction service now' in the radio screen upon starting my car. So, I'm not dealing with an oil life reset issue....

 

[econoboxrocks]

P0504 is an OBD-II diagnostic trouble code that indicates a problem with the correlation between brake switches A and B. This code can occur when the engine control module (PCM) detects an incorrect signal from the brake switch.

Symptoms Brake lights may not work and Cruise control may not work.

Common causes Brake switch failure, Powertrain Control Module (PCM) failure, Wiring issues, A blown-out brake light fuse, and A scorched-out brake light bulb.

Possible repairs

• Replacing the brake switch
• Repairing or replacing wires or connectors for the brake switch harness or circuit
• • Replacing a blown-out brake light fuse

This is just off Google. If the car drives fine, and your brakes act normally, don't panic.
If you can't get the wrench light off, and you're getting this code, it's electrical gremlins.

If your brake lights work, and the cruise works, the solution could be as simple as disconnecting the battery for a while, or replacing it if it's old. These cars are famous for throwing codes if the battery is weak.
DAMHIK

 

[dragonfly0201]

Brake lights work as far as I know. No issues with braking. From what I read about it, it indicates a failure in the brake light switch. And since I can't figure out which switch is which, that is why I posted the picture.
My question is NOT ONE code reader I used picked up that code. I had to use my Forscan software on my computer to run a diagnostic to get that code. WHY wouldn't an OBD II code be able to be found on OBD II code readers? That makes zero sense to me.
My car is a S trim level. No cruise control. YET. I plan to get that going but I need to fix this first.
I have disconnected the battery, even jumped the positive to the negative cable. This stupid light is still on. Battery tests fine.

 

[Handy Andy]

The typical simple OBD-II Code reader checks emissions, and engine, fuel, and even AC if it's programmed enough to look for it, but the "Brake light" and switch malfunctions are part of a Chassis or Body condition - so the typical OBD-I/II or any scanner won't pick up a code unique to the body style of the vehicle unless it's capable to talk to the systems affected to know this and display that code - Else you'll need to go into the Instrument Cluster HEC self-test mode to locate the specific codes for that vehicle.

The brake light aspects are to tell the system to Idle up when your leaving from stopped position onto making sure the vehicle can pull from a parked condition onto Hill-Assist and the use of ABS and Trac-Control - if both switches are not working - the system can't tell if and when the car goes into a skid, what you're trying to do to get out of the condition - so it will set that spanner light, not the Check Engine light because of the body module can't tell you more and braking is affected - not necessarily the engine side - it's OK.

So that spanner wrench light does more to tell you something else is wrong - just not with the engine - onto being a reminder light to tell you you change the oil - but since it doesn't go away, you now have another condition the system is trying to tell you about. This even affects Air and climate, temperature - even TPMS or Brake - The BCM does monitor those systems not the PCM - it's transferred that stuff and their reminders - to the BCM so it can take more control of engine functions.

The Instrument Cluster and HEC display is the Refrigerator door and all those magnets on the Post-It<tm> notepads are for the rest of the kitchen and it's staff to read. (Some may contain Recipes, but most are for reminders) It serves as a catch-all for any and all messages so it knows which light to shine, on the dashboard.

 

[dragonfly0201]

My Forscan test showed P0504. Brake Switch A/B correlation code. From what I read, it's saying there's something wrong with the brake switch. My brake lights work. No issues braking. No idle issues. What else can it be if it's not the brake switch sending bad signals to the BCM? What are the two switches on my brake pedal? One is black, one is blue/white.
What is this HEC self test you speak of?

 

[Handy Andy]

The one that Ford has for the Fiesta...

The one on the Instrument Cluster, your Pods

HEC Display.png

• Handy Andy
• Jan 4, 2024
• 1

To figure out the switches, you already know you have Brake light, so just between the two, look for any inconsistiencies like stuck plunger when you press the pedal down, or one connector seems more lifted than the other.

You have two paddles - one controls the Blue body switch while the other controls the Black one

Check to make sure your pedal is able to press in those plungers when the brake is at rest.

 

[dragonfly0201]

Ohhh how interesting. I had no idea Ford had this test feature. I will try it and see what it says.
Still do not know which switch is the brake switch...I have seen brake switches be both blue/white and black...and I have both of those, so I dunno which one is which.

 

[Handy Andy]

OK, to add more.

My Forscan test showed P0504. Brake Switch A/B correlation code.

To set that code means one of the brake switch switches that should be engaging when you hit the brakes - is not changing status.

You know the Brake light works, but have you ever tested to see how far down the pedal needs to be pressed to make that light come on?

Why?​

• Because if the brakes get applied and slow the car down, (how) does the engine know?
  • There used to be a subsystem that looked at the change in the brake light and controlled Cruise control and even affected the emissions like EGR to help with rich fuel conditions to ventilate the system.
  • Ford forked off this concept to use it also as a means to provide access to this change in status to help with Cruise Control and also added Hill-Assist - they used a separate switch to control these systems or features.
• So if the Pedal gets pressed, does it travel far enough to make it's plunger change the status of the other switch to change it's status so the system knows your using your brakes?
  • Can the Brake pedal, when released, retract far enough so the plungers throw is far enough to tell the system their change in status? If the car is started and the plungers are not seating - the system sees a result so it will try to compensate for this - during the drive cycle you might not have cruise control or it will notify you that the Hill-assist is not working System Malfunction - Service Now messages appear because it can't figure this one out.
• IT can set that code from not seeing any change in status because you don't need to press the brake pedal down far enough to make that other switch plunger move (or throw) far enough to change it's state. You can brake normally but the other plunger is not moving (it's throw) far enough to make or break contact
  • That may be from the plunger is stuck, dirty switch or it's dying on you or the aspect between one plunger and the other are too extreme in operation for the system to operate safely.
• This can cause the Cruise Control - Hill Assist and ABS/Trac-Control to work erratically or not at all because of one switch is either stuck or the pedal doesn't travel far enough to move the plunger far enough to change the condition from on to off - Off to on and back again. So it will disable these features until it's fixed

I have to tell this in this post so others whom may encounter this problem will know what is going on...it's not against you - it's a LEGACY post to help others later.

I reviewed your picture, there's little out of the ordinary to see except to know that the switches are properly seated - but one switch - the Blue one, seems to have a rear bulge - the upper white portion where the connector goes, on that body is extended above the seal of the blue side - leaving a gap. This may put the switch in a condition where it can't seat the switch to make full contact. There are supposed to be tabs on the connector contact body that seat on the blue openings - I don't see them fully seated in the window for those tabs on the body.

Look at the post with the brake assembly removed.
Might want to investigate your Blue switch - it seems it's tabs and notch are not fully seated​

Since it looks at electrical - the mechanics are OK, the contact may be too dirty or have just enough resistive or higher-ohmic contact result for the system to see any change by power thru those switch contacts. This change in height can do this - get another switch.

• Also note too, the Plunger of the Blue one is slightly more extended - that is where an old adjustable crescent wrench's gap, set thinly - can offer a means to bend the paddle to make the plunger seat better. You place the wrench jaw on the flat and gently pry up or down on the paddle - you press on the Brake pedal to pull the paddles away so you can fit that jaw on the flat to pry it up or down to adjust aspect. You can also adjust the seated flange to some degree to help with both the retracting of the brake pedal for releasing the brakes and setting trigger point for both switches at the same time.

​

When the Brake light works, that is a redundant system - but the other switch is also controlling the ability to handle Cruise Control and the effort of starting the car when the clutch pedal switches (it also has two one at the top of the pedals rest stopper and the other one is at the full bottom of when you push in the pedal to shift gears). You don't seem to have any problems with those - you can start the car so those switches work and seem to be OK.

Otherwise, the redundant part of the system that is not integrated with Brake, is for turning off the Cruise Control - that other switch does the job for you. When you tap on the brakes the light may work but the other plunger is not sending any change to the system, so the BCM sees Brake pedal - but it can't see any change in the other switch

 

[dragonfly0201]

Wow! Well, I will be investigating both switches, but the blue/white one in particular. I have had to replace the blower motor resistor in this car so far for electrical. Quite possible that switch is bad. I need to take it out and get the part number so I can find a replacement. Probably just easier to replace it. They're not that expensive.
Will update on here once I've had a chance to check the blue/white switch and replace it if necessary.

 

[dragonfly0201]

The blue switch plunger isn't coming back out all the way. It's a cruise control switch. WHY would my car have a CC switch when it didn't come stock with CC?
The black switch is the brake light switch. My lights work fine with that switch. Even with the blue switch completely disconnected. Nothing about this makes sense.
Anyway, I bought both switches and will install them.

How do I reset the computer after replacing both switches to make sure this was the issue?

 

[dragonfly0201]

Brake pedal wasn't able to depress the blue switch plunger all the way as it's not depressing correctly.

 

[dragonfly0201]

I noticed the brake switch plunger as well wasn't working as it should...do these both normally stop functioning in a car that's less than 15 years old? This one, the plunger was really tough to get to depress and I noticed also a big difference in length of the plunger as compared to the new one. Just like the cruise control switch plunger, the length was significantly less than the new one.
I'm still at a loss as to why my car has a cruise control switch when it did not come with CC. Have not been able to figure it out.

 

[dragonfly0201]

Well, replacing both switches, unhooking the battery for 15 mins DID NOTHING. I don't have a clue what to do now.

 

[Handy Andy]

Now I'm stumped - you've done what I already have done with mine (as a 2018). Mine were due to the Manual clutch and the brake pedal - but also got after the paddles and their plungers aspects to make sure that the paddles on the two pedals engaged correctly.

Which then means a minor bending of one or both paddles - you may need to verify the brake pedal can extend the plungers far enough to accomplish that "engagement" to reverse their status.

When the brake pedal is pressed, the paddles let the plungers extend - but if one is able to work but the other which was stuck in a mid-position - is not able to engage the contacts to tell the system it's working - causes this.

When they seat - then the switches revert or reverse their condition.

This thread might help understanding this - a schematic is supplied to help others know what those switches do.
https://www.fordfiesta.org/threads/need-help-to-diagnose-car-not-starting.8830/post-24050

That A/B switch condition will kill cruise control and affect the RPM when at a stop - as in, the RPM will rise to about 900~1000 RPM even when the brake pedal is pressed. When you press the Brake, its supposed to drop down the RPM to Idle speed - if not, it them means the brake pedal side is what is causing this.

IF you use a clutch, the pressing in of the clutch pedal makes the RPM go up until you hit the brake pedal or release the clutch (in neutral) as a means to help with Hill-assist or take-off anti-stall. This too affects the A/B error but you'll see PRESS BRAKE AND CLUTCH TO START message when you try to start the car first thing in the morning - then that may mean the clutch side is also not working.

 

[dragonfly0201]

I didn't even think to check the clutch switch...yes, it's a 5 speed. I have not ever thought about checking for idle speed. And no, I DON'T get a warning that says 'press brake and clutch to start'. I just get the Engine Malfunction/Engine Service Now warning. My car is a keyed start. Not push button. Not sure if that makes a difference or not.
Owner I bought the car from said she did have the clutch done...but I don't know at what time and mileage.