Hi all,
Hoping someone here might be able to help or point me in the right direction.

I'm having an issue with my 2013 Ford S-MAX. A while back, the car came up with a yellow "Transmission Malfunction" warning while driving and went into limp mode. Around the same time, I also got an "Engine Malfunction" warning, but that hasn’t come back since.

I took it to a mechanic to get the fault codes read. The two main codes that came up were:

• Low Boost Pressure
• Accelerator Pedal Sensor Fault

Observations..

• The car will drive normally for a short time.

• Then the revs start fluctuating, and the vehicle begins to lurch forward intermittently.

• After that, the transmission malfunction warning comes back and the car goes into limp mode again.

• Turning the car off and back on fixes the problem temporarily, and it will drive fine for a while before the issue returns.

• The vehicle was driven to the mechanic (About 30km away) and didnt cause any issues on the way there. 

Would appreciate any advice or if anyone’s experienced something similar. Trying to work out whether it’s an electrical/sensor issue, a boost leak, or something transmission-related.

Thanks in advance!

I've been told by the mechanic that low boost can throw up the Accelerator Pedal Sensor Fault as the ECU is expecting a certain value of boost depending on how far the accelerator is pressed. He also said that this can "confuse" the transmission and hence why im going into limp mode. 

4 hours ago, moneyp1t said:

The two main codes that came up were:

• Low Boost Pressure
• Accelerator Pedal Sensor Fault

The other two are just as important!

My money is on a broken wire somewhere.

Check the main connector under the LH front wheel arch, they tend to get broken wires there

5 hours ago, moneyp1t said:

I've been told by the mechanic that low boost can throw up the Accelerator Pedal Sensor Fault as the ECU is expecting a certain value of boost depending on how far the accelerator is pressed. He also said that this can "confuse" the transmission and hence why im going into limp mode. 

Intermittent communications issues between modules will cause these issues too.

Check the wiring before you throw money at it

10 hours ago, DaveT70 said:

 

Check the main connector under the LH front wheel arch, they tend to get broken wires there

 

Thank you for your reply. Would you presume this is causing all the trouble codes?

I will have a look under the LH wheel arch for any damaged wiring and will report my findings.

Unfortunately, these vehicles are not very common in New Zealand—it's a struggle to find anyone who can correctly diagnose and repair any issues.

Might I add: my RH high beam is also only working intermittently—it will turn on briefly when toggled, but will switch off after 0.5 seconds and won’t come back on until the vehicle has been turned off and on again. Check my other post for more details.

Could this all be related?

Thanks in advance.

8 hours ago, moneyp1t said:

Could this all be related?

There's a chance.

The vehicle could've had front-end impact damage, which is causing wiring issues.

The best bet would be to get an auto electrician to check all the wiring for continuity issues, especially the communications circuits

Ensure the battery performance is good and the earth(s) to body performance is good too👍

Could this also be the dreaded BCM water ingress from windscreen washer pump? Perhaps check that?
https://www.youtube.com/watch?v=eYGlM1gYzuc&t=21s

And some hints on wiring issues under the wing by the PCM:
https://www.youtube.com/watch?v=ikDCVb93mk0

 

Edit: at the moment all roads seem to point to that area?

 

Just posting an update in case anyone else is dealing with similar issues.

Summary of Issues and Observations:

Car drives normally for a short period, then:

• Engine revs start fluctuating rapidy (around 200 - 500 rpm) 
• Vehicle begins lurching forward intermittently
• Transmission malfunction warning appears, and car enters limp mode
• Turning the car off and on again temporarily resolves the issue; problem returns after driving for a while

Additional background:

• About a month ago, the car’s battery died completely (someone left a light on)
• Battery was replaced, but it kept discharging if left unused for a couple of days
• Noticed a drop of fluid on the driveway—turned out to be transmission oil

Recent Findings and Potential Causes:

• Mechanic found a 1 AMP of parasitic draw when the vehicle was off (explains the battery drain)
• The culprit was a poorly installed “battery booster” (done by a previous owner), which was drawing power continuously and was miswired to a fuse that interferedwith the car’s boost (Hence the low boost pressure code)
• The transmission issue seems related to a leaking input seal (mechanic unsure if it’s the inner or outer seal)
• The leak led to low transmission oil, which likely caused the transmission solenoids to malfunction—makes sense, since the transmission relies on hydraulic pressure from the oil to operate properly ( I presume....?)

Next Steps:

• Mechanic is working on repairing the input seal/leak and sorting the wiring for the battery booster
• Expecting to get the car back by the end of next week
• Will report back with any further findings or if the problem persists

I just hope the low oil hasn't damaged this vehicle delicate powersh*t driveline. 

Hope this helps anyone else experiencing something similar.

Should have asked if oil level, filter, oil changes had been checked with ANY Powershift problems (as it's pretty much all of the simple things you can do (along with cable adjustments and wiring checks)
Please come back and confirm the fix, Thanks!