Help! Permanent fault, Input Speed Coherence P1743

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2040Damian
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Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 11 May 2019, 13:43

Google is sooo useless lately! I’ve got this new error now & I've no idea what it is! I’ve put an image up of the fault code in Lexia but I don’t really know where to go from here. If it helps I’m experiencing a similar issue to clutch slip but only when shifting gears. I’ll switch up a gear and the car will rev high but not bite immediately. It’s a 1.4 C2 Sensodrive
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GiveMeABreak
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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by GiveMeABreak » 11 May 2019, 14:10

VIN please.... I need to confirm exact type - but I suspect it will be similar to the C3 system:
Fault codeP1743
After sales description of the fault codeGearbox input speed signal fault: Coherence
Description of the diagnosticsSpeed outside range
Acceleration of the speed outside range
Impossible value when comparing the measured input shaft speed with the calculated vehicle speed with a gear engaged
Time for appearance of the diagnosis: 5 seconds
Context of appearance of the fault codeVehicle in motion
Technical precision on the context of appearance of the fault code-
Conditions of disappearance of the fault-
Down-grade modes if fault presentDriveability impaired
Gear engagement time too long
Reconstruction of the information from the engine speed sensor and vehicle speed
Loss of the wheel slip detection function
Switching on of the warning lamp and/or warning message-
Main customer complaints likely-
Suspect areasInput shaft rotation sensor
Electrical harness
Controlled manual gearbox ECU

2040Damian
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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 11 May 2019, 14:26

Vin is VF7**************[VIN obfuscated, can be read by forum staff]

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by GiveMeABreak » 11 May 2019, 14:58

Ok, so yes, confirmed - same system and same fault code. So you have the suspects, if the Gearbox Input Speed Sensor is faulty it will affect the data sent to the ECU and therefore it can't adjust for clutch slipping. So may be worth investigating that first....

Gearbox input speed sensor connection (1662)
Role
The sensor supplies the gearbox ECU with the gearbox input speed.
This information allows the gearbox ECU:
  • To calculate the slipping of the clutch (difference between the engine speed and the input speed)
  • To calculate the clutch’s load-bearing point
  • To control the clutch actuator
  • To check the completion of synchronisation of a gear
Description
The sensor consists of a magnetic core and a winding.
The information supplied to the gearbox ECU is an alternating voltage which varies according to the rotational speed of the gearbox input shaft.

Electrical special features
Allocation of channels of connector:
  • Terminal 1 : + signal
  • Terminal 2 : - signal
  • Resistance between channels 1 and 2 : 800 ohms (approx.).
  • Features of the signals emitted: Variable frequency alternating voltage.
CAUTION: The sensor wire is not screened, therefore always follow the correct harness route.

Location
The gearbox input speed sensor is located opposite the teeth of the second gear pinion of the primary shaft.

As for parts - I think it might be part 13 on the diagram below:
C2 Gearbox Input Speed Sensor.PNG
On the electrical diagrams it is item 1662, which sort of resembles the location on this diagram:
C2 Gearbox Input Speed Sensor B.PNG
It could of course be the ECU or any of the other issues - but if it is the Gearbox Input Speed Sensor, and it is the part 13 on the first diagram, then that is part number 2529F8:
C2 GB Sensor.PNG

2040Damian
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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 11 May 2019, 16:36

That's awesome thanks! I actually think it's number 7 based on the results I found searching for gearbox speed sensor Which look like these https://www.mister-auto.co.uk/sensor-sp ... eo/255304/

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 11 May 2019, 16:39

Actually 7 may be the reverse sensor....

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by GiveMeABreak » 11 May 2019, 19:29

7 is the reversing switch

RichardW
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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by RichardW » 11 May 2019, 20:32

Given it's reading an input speed of 0 when engine speed is 1910 and clutch engaged, it certainly appears to be suspect!

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 12 May 2019, 00:16

Thanks for the help with this, I’m gonna order the part you’ve suggested & pray it’s right & fixes the problem 😂😂

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by 2040Damian » 13 May 2019, 17:35

OK so update on this problem, it was indeed the sensor... however it was because the clip that holds the cable on is perished so the cable had simply slipped off. That's sorted now! Took it for MOT today & it failed on sill rust :( Booked in for Thursday to get a bit of welding done & I've also got to service the drums on the back as they seem seized then it's back to the garage for it's re-test

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Re: Help! Permanent fault, Input Speed Coherence P1743

Post by GiveMeABreak » 13 May 2019, 18:17

Great - that's at least sorted that and good to have the feedback and update for reference. Best of luck with the welding.