Hi all,

I am receiving the error codes P0698-62 (Sensor Reference Voltage C Circuit Low) and U0073-21 (CAN Communication Bus Fault). 

Symptoms:

- With the EGR Plugged in, car will idle for 10-15 mins before cutting out and throwing the codes.

- With EGR unplugged, car will idle for approximately an hour before cutting out and throwing the codes.

• After fitting the relacement ECU today, it 'choked/misfired' and nearly cut out about 40 mins in before stalling at 59mins idle.

- The car will NOT restart (in either of the above conditions) unless i've cleared the codes with ForScan. It will, however, restart sometimes if left alone for a period of time without clearing the codes.

- It's also worth mentioning that the red oil pressure warning lamp illuminates when the car stalls.

Work so far:

- Bought a brand new Bosch battery (old one was kaput anyway) no difference.

- I have replaced the EGR valve to no avail, and it makes little difference (as noted above) when unplugged anyway.

- I have replaced the crankshaft position sensor to no avail.

- I have replaced the ECU and had the data transferred from old to new, again, to no avail.

- I have checked performance of MAF sensor on ForScan and there are no issues.

Work i'm considering:

- I have not yet replaced the fuel pressure sensor.

Points to note:

- I have checked all previous posts concerning DTC 'P0689' on this forum. Information from others states that it's an issue with the 5v line but I am not an electrical specialist by any means and resolutions have not been shared by original posters.

- Interestingly, this started to happen after I replaced the injector seal on cylinder 2. When I pulled out the injector it was covered in a sticky tar, which was all over the original seal. This may be entirely unrelated, but thought it worth mentioning.

- I have had this issue misdiagnosed by both a local garage and a recommended autoelectrician. As this seemed to be happening only when the bonnet was closed, the autoelectrician said it 'must' be the ECU. Unforunately this misjudgement cost me an additional £200. The original mechanic said that he suspected the EGR (i've since binned the old one after replacement and now realise there was nothing wrong with it).

 

Any help would be greatly appreciated. I work for the NHS and my job is 1 hour 30 min drive from home. I've been stuck on this problem for the past month without any resolution. There is only so long I can cantinue to use brother's car. I'm on the edge of scrapping this fiesta an seeing what I can afford as a relacement T_T

 

Any help on this?

I don’t know the answer.  But it is correct that oil pressure light comes on when stalls.  It has a switch that checks oil pressure. If engine stops, pressure falls, switch activates light. That is normal and correct.

Have you read this which I found using Google. https://www.justanswer.com/uk-ford/aie3i-fiesta-1-6tdci-van-57-plate-along-drive.html

12 hours ago, isetta said:

Have you read this which I found using Google. https://www.justanswer.com/uk-ford/aie3i-fiesta-1-6tdci-van-57-plate-along-drive.html

Thanks isetta, yes I believe I have read that post but completly forgot about it. I've found a very well reviewed mobile auto electrician who will be tracing the fault electrically. As I wrote above, I have yet to replace the fuel rail pressure sensor, but it's on the list and the last thing I have to try. I have now bought a replacement car but hopefully will claw some money back once if we can get it running (and not stalling) again. Thanks for your input and any further advice from others would be greatly appreciated. I intend to stay by the autoelectrician when he is able to come and do the work so that I can update this thread with the answer for others. From what I have been able to find this is a fairly common and dangerous fault on the MK5's that happens without warning. In some sense I would rather it had been the alternator as at least I would have had some warning before losing all power.

Thanks again,

Alistair

On 12/23/2021 at 6:36 PM, Alzatar said:

Hi all,

I am receiving the error codes P0698-62 (Sensor Reference Voltage C Circuit Low) and U0073-21 (CAN Communication Bus Fault). 

Symptoms:

- With the EGR Plugged in, car will idle for 10-15 mins before cutting out and throwing the codes.

- With EGR unplugged, car will idle for approximately an hour before cutting out and throwing the codes.

• After fitting the relacement ECU today, it 'choked/misfired' and nearly cut out about 40 mins in before stalling at 59mins idle.

- The car will NOT restart (in either of the above conditions) unless i've cleared the codes with ForScan. It will, however, restart sometimes if left alone for a period of time without clearing the codes.

- It's also worth mentioning that the red oil pressure warning lamp illuminates when the car stalls.

Work so far:

- Bought a brand new Bosch battery (old one was kaput anyway) no difference.

- I have replaced the EGR valve to no avail, and it makes little difference (as noted above) when unplugged anyway.

- I have replaced the crankshaft position sensor to no avail.

- I have replaced the ECU and had the data transferred from old to new, again, to no avail.

- I have checked performance of MAF sensor on ForScan and there are no issues.

Work i'm considering:

- I have not yet replaced the fuel pressure sensor.

Points to note:

- I have checked all previous posts concerning DTC 'P0689' on this forum. Information from others states that it's an issue with the 5v line but I am not an electrical specialist by any means and resolutions have not been shared by original posters.

- Interestingly, this started to happen after I replaced the injector seal on cylinder 2. When I pulled out the injector it was covered in a sticky tar, which was all over the original seal. This may be entirely unrelated, but thought it worth mentioning.

- I have had this issue misdiagnosed by both a local garage and a recommended autoelectrician. As this seemed to be happening only when the bonnet was closed, the autoelectrician said it 'must' be the ECU. Unforunately this misjudgement cost me an additional £200. The original mechanic said that he suspected the EGR (i've since binned the old one after replacement and now realise there was nothing wrong with it).

 

Any help would be greatly appreciated. I work for the NHS and my job is 1 hour 30 min drive from home. I've been stuck on this problem for the past month without any resolution. There is only so long I can cantinue to use brother's car. I'm on the edge of scrapping this fiesta an seeing what I can afford as a relacement T_T

 

So after spending stupid money and time on this problem and going through three garages and two 'auto electricians' (one actually had testing equipment/multimeter, the other was just a tyre kicker but neither of which could/would locate the problem), I finally located the issue myself.

I worked my way through every part on the C-Curcuit and ended up having to dig deep at the back of the engine to remove and inspect/replace the fuel rail high pressure sensor. Turns out the three electrical pins were corroded and I replaced it with a £12 second hand part... so, in one sense, this is fantastic as the car is fixed, but it is 'bitter sweet' as I've spent a small fortune on incompetent mechanics and autoelectricians. Both in paying them for getting it wrong and buying the parts they recommended (included a replacement ecu and then having it cloned!?)

This was my issue...

 

 

Thanks for posting this, there are so many threads where we never find out if problem was ever fixed, and hope it helps someone else in future. 

On 4/11/2022 at 6:34 PM, isetta said:

Thanks for posting this, there are so many threads where we never find out if problem was ever fixed, and hope it helps someone else in future. 

I noticed this as a common theme on the forum, not just this one but other car forums too so I was determined to come back and post the solution if I found it 🙂

Most forums are the same, people come on to get information but never give anything back, they have got what they needed and only come back when the next problem arrives.

Hi! I’m unsure if you’ll see this message but wanted ask a question: after you replaced the fuel pressure sensor, did the fault ever comeback? 
I had a garage change the EGR valve and then spent most of the day waiting to get rescued off the M1