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Mike, Jaguar Technician
Category: Jaguar
Satisfied Customers: 39198
Experience:  Tech Expert
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I have fault code P0642 (sensor reference voltage A circuit

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I have fault code P0642 (sensor reference voltage A circuit low) The question is where is the supply to the sensor fed from and what should the true voltage be.?
Hello and Welcome -

My name is XXXXX XXXXX Im happy to help you .

Your other / duplicate questions have been closed - this is to prevent you being charged twice -or more, for the same question.

Can I just ask you to please give me the cars Full reg number - so that I can see exactly which management system it has - then we can progress -

Kind Rgds, MIKE...............................................
Customer: replied 4 years ago.

Hello Mike my Reg is FS04 ADS

Hello Alan -

Thank you for your reply / info.

Ok - the fault code you have - the P0642 - relates to a fault with the fuel tank unit -

The fault will not clear even using diagnostic equipment, until the actual fault has been addressed / fixed.

I will give you the fault finding wrote up from the Jaguar Tech data on this - that is as follows :

OBD Code P0462 = Fuel level sensor.

The fuel level sensor is mounted in the fuel level sensor unit. The sensor detects a fuel level in the fuel tank and transmits a signal to the ECM or PCM. It consists of two parts, one is mechanical float and the other side is variable resistor. Fuel level sensor output voltage changes depending on the movement of the fuel mechanical float.


Possible symptoms of OBD code P0462
- Engine Light ON (or Service Engine Soon Warning Light) Driveability issues possible.


- Fuel level sensor circuit harness or connectors is open or shorted - Fuel level sensor may be faulty. The fault code is generally activated on detection of the following conditions: An excessively low voltage is sent from the sensor is sent to ECM / Pcm.

Causes - Fuel tank module - wiring to / from module / Pcm.

So- the wiring from the Pcm ( computer ) should be checked through - the connections on the Pcm - and at the fuel module ( at the tank ) need to be checked for any wiring / connection issues -and any such issues addressed - but if nothing is found to be wrong there, he needs to renew the fuel tank module / unit ( in the tank )

Let me know how you get on if you wish- or get back to me if you need anything else at all...

Kind Rgds - MIKE.

...Meantime..............Please do click on the "OK/ Excellent ratings" for me as that's how Im credited for helping you - Thank you in advance for that...

You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..

Rgds, MIKE.
Customer: replied 4 years ago.

Hello again Mike are you saying that code P0642 is the same as P0462
or have we got crossed line with fault codings.

Hello again Alan..

My sincere apologise - fingers getting mixed up ! In which case- you need to ignore the above!

Ok - so - fault code that you have - P0642.

From the Jaguar Tech - again - the definition for that is as follows:

Sensor Reference Voltage "A" Circuit Low

What does this mean?

OBD Code P0642 refers to :
The ECM has detected that the 5 volt reference voltage is too low


Possible symptoms of OBD code P0642
- Engine Light ON (or Service Engine Soon Warning Light)


Possible causes of OBD code P0642
- ECM Short circuit condition - Shorted.

So this is , most likely a fault with the Ecu / Ecm ( main engine management computer) and usually is - but- again - the wiring to it -its connections etc should always be checked first - and , inc , the earthing on the car - earth points.. very important.

"Reference voltage" is for sensors on the car - which are always up to 5v ( not 12 ).. If the Ecu is producing this code ( the 0642 ) - then other than wiring faults - which can cause any given fault... then that relates to the Ecu as faulty in this case.

These Ecu units are not at all cheap - as a general rule, garages will send the Ecu in a suspect case for test and then subsequent repair. There are specialist companies that do this work ( it takes specialised equipment ) - There are many that advertise on the net / google etc... or I can give you a contact - The company I have in mind is on 0 1 6 3 4- 6 8 7 2 2 2 ... They are based in Kent area and operate a postal service. So you need then to give them a call and they will talk you through -inc costs etc. Again - costs of repair / recon work is considerably cheaper than a new Ecu / Ecm - and doing that saves coding costs etc etc...

So - I do apologise once again unreservedly for my error earlier... and again - if you need anything else - just let me know.

Incidentally - the same is true with this code - the code / light etc will not clear - not until the fault itself is addressed / fixed.....

Kind Rgds, MIKE..

.... Please do the "Ok ratings" for me Alan as thats how Im credited for helping you - Thank you once again advance..

All the very best ... MIKE.

Mike and other Jaguar Specialists are ready to help you
Customer: replied 4 years ago.