C5 X7 Rear Parking Sensors: External rear right sensor coherence

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mikevybiral
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C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by mikevybiral »

New to me 2008 C5 X7 2.0 HDI VTR+

Fault code: 98D3

I gather this suggests a short circuit to +ve.

(Use of the word 'coherence' suggests to me a mistranslation from French? What should it be?)

So, where to look?
Could this be a defective sensor elsewhere? (I've replaced the rear right sensor).
Could the fault be in the loom? If so is there a common point of failure?
Could the relevant ECU (next to spare wheel) be at fault?
I'd be grateful for some pointers.

Thanks,

Mike
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xantia_v6
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Re: C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by xantia_v6 »

'coherence' faults generally signify that there is a sensor that is giving a reading that is within the operating range of the sensor, but implausible under the current conditions, perhaps conflicting with the signal from another sensor, or perhaps just not compatible with the expected state of the system.

Water in parking sensors might well cause this kind of issue.
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GiveMeABreak
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Re: C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by GiveMeABreak »

I think you'll find that that should be 9BD3 - it's not an '8'. It's basically saying your Front Right Outer Sensor is shot and needs replacing.

A simple test is to put the car in reverse with the ignition on and get out and gently place your finger very lightly near to the surface of the sensor. If it is active, you should feel a faint pulsing. Compare that with the others.
mikevybiral
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Re: C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by mikevybiral »

I've disconnected the parking sensors and tested the loom for short or open circuit to the RH sensor connector. No fault found. I've moved the sensors around. Now Lexia shows fault ABC8, rear R sensor shorted to +ve.
I'm at a loss?
Hell Razor5543
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Re: C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by Hell Razor5543 »

If you swapped the sensors around did the fault follow the sensor? Each sensor is a discrete component in the loop, covering part of the area to be 'looked' at. Some cars (depending on the equipment level) can show you roughly where an obstruction is (my van just beeps when something is getting close, but Michels' Skoda Octavia shows you (on the radio display) where the obstruction is).

I have had to (in my line of work) swap parts between a suspect system and a known good one. As soon as the fault moves between systems I know what part is faulty (the one I just moved).
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GiveMeABreak
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Re: C5 X7 Rear Parking Sensors: External rear right sensor coherence

Post by GiveMeABreak »

mikevybiral wrote:
19 Jun 2019, 19:16
I've disconnected the parking sensors and tested the loom for short or open circuit to the RH sensor connector. No fault found. I've moved the sensors around. Now Lexia shows fault ABC8, rear R sensor shorted to +ve.
I'm at a loss?
I do apologise - there are a hundred codes for the system and I actually gave you the wrong sensor location for the original code. I have corrected my original post so it does not cause a problem for anyone else.
The correct information for the original sensor is below, and also the code you are now receiving. I suggest you put the rear sensor and loom back and look at the front one as below.

9BD3 is the Outer Right-Hand Front
ABC8 is the Outer Right-Hand Rear