wrench, airbag light and limp mode once warmed up, clears once cooled down.

[Forestlump]

Hello,

I'm struggling to find the cause, please would someone help?

5.0 2017 manual car with Paxton/ bap, catless Lths, 18 manifold.

Starts and drives fine for about 10 minutes and then get the wrench and airbag light.

Forscan shows codes
p2128 Throttle pedal voltage correlation
p2138 Throttle pedal voltage high
b00A0 Occupant classification system
U0401 invalid data from ECM/pcm.

codes all reset once car has cooled down and stay off until it warms up again.

on the oscilloscope on Forscan I can see the point at which the fault happens, throttle pedal voltages APP1 + 2 are smooth and zero error untill that point (after driving for about 10 mins). Then the voltage from APP2 jumps 1.5v and the error goes full scale and car goes in to limp mode. APP2 voltage is then bumpy/ dirty and codes won't clear until it cools down again.

It's like something switches on after a while and is dragging down the 5v but only on Throttle pot APP2. Though the 5v ref never wonders from 5.01v (I'm wondering if there is 2 5v busses and something on bus 2 is shorting)

Battery is mint, connections are all clean.
Changed pedal for low milage ford spare but fault is identical.

Disconnected rear O2 sensors, vortech bap, A/c pressure transducer, still the same.

disconnected passenger seat.

checked all wiring, as far as possible.

With the Forscan oscilloscope showing throttle voltages and when the faults triggered, I've disconnected near enough everything related to the 5v to see if it's a short but nothing clears it.

Any ideas?

I've read of an identical fault but the guy traded in the car before finding out what it was, ford had replaced pcm and diagnosed the loom. I'm 100% it's not the loom as it's repeatable.

See oscilloscope of throttle voltages
APP1 (Red)
APP2 (GREEN)
pcm throttle command (blue)
Throttle pots error (purple)


Any help would be gratefully received.

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[Forestlump]

Forgot to say, car hasnt been fiddled with for over 2 years, has done 8k miles since charger installed. Fault first happend while driving at 50mph.

 

[5.0_Lojos]

When I first got my procharged 2016 I did a 1 2 3 shift all the way to redline and the car went on "limp mode" out of nowhere, the gauges lost readings but car still drove a few miles till I got home (Scarry situation) on fairly new purchase. At the time I didn't even know what limp mode was, I thought I had disenegrated my "Oil pump gears" after online reviews I stumbled on the "limp mode" safety feature. I of course was panicking and drained the oil and cut oil filter hoping to not find any metal particles 🫣 Also, the car wouldn't advance during the shift (it felt as if it were on ice) gliding. I eventually changed the clutch and got a real tune by Wengerd Performance haven't had an issue since.

 

[Forestlump]

Id imagine you were getting clutch slip as since the charger install, 1st and mostly 2nd gear should make the tyres slip.

The car has a lund tune and has been spot on since day one for over two years. I'm in the UK and Lund did it remotely.

This fault however is nothing to do with the tune.

I'm going to try doing an as-built software reboot on the ocsm today, though I think my problem is a ground fault on a sensor or the module itself.

 

[luca1290]

I'm going to try doing an as-built software reboot on the ocsm today, though I think my problem is a ground fault on a sensor or the module itself.

I see you are already on a good path to solve it by yourself.
Check the Wiring Harness sections of the Workshop Service Manual and confirm you have proper resistance readings from grounds.

 

[Forestlump]

Hi Luca,
Il do that, thanks.

Do you have access to the drawings?

Thanks for your time

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