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Coolant Sensor Low Voltage

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I have another one for ya about the '11 F650 which I operate.


Pertinent back-info:


I am the operator, not the mechanic, ours is stumped so here I am.

Ford dealership will not tend to this vehicle,  due to a post modification.


Purchased in 2015, dropped in a Cummings 6.7, and deleted the DEF (exempt in this state)(2011 series DEF system is a known failure).


All was fine until '18 when a Dodge Dakota wiped out the front end, as deep as the cooling fan.


Boss went for collision repair, as it was deemed not a total.


The problem now (which the collision shop just says "don't know"), we are getting low voltage from the pcm to the coolant sensor plug at the reservoir.

It should be a 5v reference voltage, but mechanic is only getting 4.2 from the pcm. Ergo, we get code 111, sensor voltage to low. Mechanic is indeed getting proper ohm flow within this circuit.


The reservoir tank is new (aftermarket, as shop said OEM tank does not exist), the sensor and it's connector are new with the repair, as well as a new replacement sensor and connector also employed.


I just don't see only one single aspect of a pcm being wrong from the collision, it seems it would be multiple failures, the whole rest of the system in relation to everything of the system works as should, just not the sensor, which now has both amber and red engine dash lites in use.


Any thoughts?






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Guest Matt

I have ran into issues like this with cars and trucks. Disconnect all ground wires you can find under the Hood, clean the surface, and retighten them down. 

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Ford has a very low failure rate for their PCM components. If the harness has been disconnected, I would start from scratch as if you were just initially diagnosing the problem.

Are you using a pin probe kit to check your resistance? Are the pins from the PCM connector all properly aligned? It is very easy to mash a pin, thus have a connectivity problem. Do not ask me how I know! Do you have a factory repair manual from Ford. Their workshop manuals are pretty good at providing tolerance ranges for checking harnesses.

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Thank you for the replies.


Mech has went thru the connections, all looks good.


I took a couple days off, but I did see the truck still at the shop this eve, bummer, I'll find out if any luck tomorrow.



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