Rear back-up sensor issue

[db_tanker]

So I have been having an intermittent issue on my Drivers side outboard back up sensor in the bumper. It will work fine for 2-3 days or more...then out of the blue it will go full red like there is an obstacle close.
I've wiped down the sensor in case there was any kind of film blocking the emitter - no change.

Also there is no warning/error message being posted on my Ford Pass.

I got under and checked - plug is solidly connected and no visible damage. I'd like to go ahead and get a replacement since they don't seem to be that much but I'd like to know if anyone has a bench-test they can run on these maybe? What would the resistance be maybe on a DMM?

D

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[airline tech]

Have you disconnected and cleaned the connector?
Being that you are getting only (1) sensor to fault, I suspect the (Middle) Pin #2 may have a dirty connection.

Pins 1 & 3 are a shared circuit with the other sensors, but you may have an issue from the (Splice) points from the splice to the LR Outer Connector (Pins 1 & 3)

My Autel scanner displays the Park Sensor PID's, but I would have to hook up to see what the PIDs actually show

As far as Ford Pass, not giving you ant messages, you may be able to Pull a code from your scanner / Forscan, now it may clear with a ignition cycle, so it would be best to hook up while it is faulting before you turn off the ignition. It may or may not hold this as a history code, you have to catch it (Live and Active) to see a code.

Wiring Check

There are a few (Inline) connectors between the BCM and Sensors, one of those connectors can have a bad connection. (For the Sense - Pin #2) Circuit
Each Park Sensor has its own individual sense circuit.
Being intermittent, I suspect a dirty connection.

Ignition OFF:
If you disconnect BCM Connector: C2280E and the LR Park Sensor (outer) Connector C4009
You can do a quick wire check for continuity.

C4009 BCM C2280E
Pin 1 -----------Pin 26
Pin 2 -----------Pin 23
Pin 3 -----------Pin 27

Results should around be 3.0 Ohms or less.

The easiest way to do this would be to (either end) of the wire, Jump that pin to ground.
(WITH BOTH CONNECTORS - DISCONNECTED)
Then the other end - Red Probe to the matching PIn and Black Probe to Ground
If one is HIGH resistance, then that is the wire with a bad connection.

If High Resistance:
Then you will need to split the harness up to find the bad section
Via 3 Inline connectors, 2 of them are external and one is internal of the cab

C405
C422
C1147 - Location if needed

Here are the (2) external C405 and C422

More details of those connectors (If needed)
These 2 connectors have a history of water/corrosion intrusion for various systems.
Disconnect and clean them if you show HIGH resistance with the meter results.

There is not a (Bench Test) - Resistance for the Sensors (Known Values)
But you could possibly do a side by side compare between the Left Outer and one of the other 3 sensors.

Connector Disconnected and Check the Sensor Pins - Ohms Scale

At the sensor (Internal) - Pin 1-3 / Pin 1-2 / Pin 2-3 : and compare Ohm reading results between the 2 sensors.

 

[Mlemos89]

I have the same issue with my left most sensor on rear bumper. Sometimes it is fine, somes times yellow with nothing behind me, and sometimes red and beeping at me with nothing behind me. Also visually inspected and see no issue with it.

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