2014 1.0 ecoboost 125ps cold start issues P0237 fault code

[DanUK]

Hi,

need some diagnostic gods to help me out.

Car: I have a 64 plate Ford fiesta 1.0 ecoboost titanium. 125bhp version. 68k miles. 3 door.

issue: intermittent “service now” or engine management light with rough idle and lack of power.

OBD code: P0237 “turbocharger/supercharger boost sensor A circuit low”

So this issues only occur when starting it. When it first did it about 6 months ago it went into limp home mode on start up with a rough idle and lack of power. Had to take it to a garage who replaced a MAP sensor. It seemed to work for about 3-4 months.

unfortunately, it happened again. Similar rough idle, and stuttering on trying to rev it. Occasionally cutting out completely. The “service now” light came on. However, I turned the engine off and on a few times and it came back to life, with the light going off. It’s happened a few more times too, sometimes if I just rev it for a bit it seems to sort itself out and becomes absolutely normal again. Sometimes I have to restart it. Occasionally the engine management light will come on too, but this goes once I do the restart.
The fault code is always the one above. I changed the MAP sensor and what I thought was the boost sensor. (See photo below) But this did not work. I’ve done a full service with oil, filter, air filter, spark plugs, pollen filter, full coolant change, but with no joy. I took it to the local garage again, they couldn’t work it out either and said bring it back once it does it again and charged me £90. 🤣

Just to clarify, inbetween these episodes the car drives perfectly. Lots of power, normal idle. In the normal temperature range and coolant level isn’t going down.

I will attach a photo of the fault code. And the sensors I replaced. I’ll also add a video link. Any help appreciated.

https://youtube.com/shorts/En0c-1XnX-Q?si=zPVrpK2qmM1dSokG

 

[Handy Andy]

With the systems self-diagnostic, and the mechanic replacing a "MAP" sensor.

The issue of A Circuit Low usually tells me the sensor used to determine the boost or regular/normally aspirated and the difference between - that sensor is in the intake pipe.

For it to get damaged, or the wiring to it, usually means something struck the lower cool air intercooler pipe (heat) ex-changer - it means you'll have to test the connector for this sensor - at the sensor - to see if it can send a voltage and if possible, please test the connector installed on the sensor also - to see if the voltage the ECM is sending to it - is not dropping to zero - which if that was the case, the sensor got whacked and you'll need to put a new one on, simply drop in a new one - and retest the connector installed on it again to see if the sensor is properly wired in.

 

[DanUK]

Thanks for the reply. Is the sensor you talk about on the intake pipe the one labelled “boost sensor” on the picture above?

I’ve just bought a multimeter off Amazon and waiting for it to be delivered. I’ll get checking once it’s arrived.


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[Handy Andy]

Since he's already replaced the MAP sensor, the other one in the pipe is the one that needs to be checked that it's getting and using a voltage (a variable output reference) the PCM can see to adjust Air to Fuel ratio (an anticipatory event) - that it is variable (as a result) as you move the throttle - else it will go into a limp mode and or if not already - stay in that limp mode until that code is cleared.

 

[DanUK]

UPDATE

so the other day the car complete cut out on the road. Wouldn’t even turn over. No smoke or anything. EM Light came on. Then it started turning over but wouldn’t fire up. Ended up taking it to Ford who found a chaffed wire under the battery compartment which was grounding out of the chassis. They sorted it for £300… and it’s been fine since. I wonder whether this could have caused the intermittent start up issues described above. This hasn’t happened since, but it’s only been a few days.


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[Handy Andy]

The "Under the battery compartment" tells me the wiring was suspected.

Not uncommon, but not always a traceable condition - as per other avenues having been tried first to narrow down the answer to the end result. Being that, of that spot of where - when you look at the battery, the box it's in, and locate several connectors in and around BELOW the battery - does the issue come more clear.

Your main Battery Negative Ground cable that bonds the electrical part of the engine block to the frame and battery negative is over by this area on the engine.

Glad to see this was not a total failure, but as fixable one - versus having rodents take out the wring harness in several areas causing far more problems and the inconvenience - then subsequent justification on whether to keep the car, or let it get eaten alive by the rodents.

Thank you for getting back with us on this - so the "Circuit XXX Sensor XX low" condition is something more related to wiring and the failure of the sensor to send data back to the ECM/PCM so it knew how to work and what to do to keep networking with the other systems.

It sounds like most of this problem is fixed, however, one of the few the Motor Mounts (there is one there on the transmission side) is located under the battery - I hope that is in good condition so the support beam that comes off that left side strut/pillar frame brace - is not jeopardizing the whole effort. That if the motor mount failed or came loose and separated could cut the harness near where the fix was done.

Might be wise to have the mechanic inspect the engine support brace member that goes across and is part of the undercarriage that supports the motor and transmission - make sure it is not in too bad of shape.