using DS18B20 Sensors in automotive application reliability issue (Mazda Bongo)

My system has been in use for almost a year. I have 5 sensors sourced from china/ ebay ( water proof? sealed stainless tubes) in various positions around engine, gearbox (Auto) and radiator
Recently 4 have taken to intermittantly show the 85 error signal but only with engine running (diesel 4wd) engine off all sweetness and light.
I am running the arduino via USB and a usb convertor to 12V (leisure battery not vehicle battery)
is it a sensor issue as 1 is totally happy and 3 have recently started playing up (only with engine running)
or a Voltage issue
(LB is solar charged) and split relay charger.
Cheap USB /12V device
or something else

85 is an indication of could not connect IIRC.

Can you check if all wires are 100% OK? the vibration of a running motor can cause damage to soldering.

85 is the temperature setting at power up of the device. If you don't give the device enough time to do a conversion after power up, it will read as 85. Make sure your code is allowing sufficient time for the conversions.

Pete

The 85 message occurs for 1st run then will work ok
the connection question is important
my 4 problem sensors join in the engine compartment the other joins outside nearer the arduino.
I have something to look at
thanks

Remade fresh connections, soldering 4 sensors together then soldering arduino connector wires to each and heat shrink over each connection then tie wrap to sensible positions.
Been in use for over a week with no error mesages just working as it should.
Thanks