Reverse lights not working - Electrical (Mk4 Mondeo) - TalkFord.com

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Reverse lights not working


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8 replies to this topic

#1 Yipsnacle

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Posted 13 October 2019 - 06:01 PM

Hi, I’ve got a mk4 zetec with a powershift gearbox, the reversing lights are not working, the powershift does not have a reverse light switch on the gearbox, no fuse or relay indicated in the workshop manual, bulbs are good and the rear sensors are working fine, has anybody had the same prob or could point me in the right direction.

Ford code C1120 (short circuit to positive or open circuit)


Edited by Yipsnacle, 13 October 2019 - 06:15 PM.


#2 mike4369

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Posted 14 October 2019 - 01:55 PM

Have these ever worked?



#3 Lepsu

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Posted 11 February 2020 - 07:05 PM

Hey! I have exactly the same issue. Have you found out the problem?



#4 PURPLE_2L_LX

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Posted 16 February 2020 - 04:55 PM

Is the reverse switch built into the gearlever housing?


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#5 Lepsu

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Posted 19 October 2020 - 09:21 AM

I don't know.. forscan says that when i put reverse gear on, "reverse switch is switced on" or something like that. I think there's not any mechanical switch on gearbox.

#6 TreborB

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Posted 19 October 2020 - 10:35 AM

Hi, I am NOT certain what causes the reverse lights to work but there is no reverse light switch anywhere.

I am of the opinion they are controlled via the position of a cogged wheel in the centre console and when the lever is in the R position signals are sentr to the TCM (trans control module) which I presume transmits the signal via canbus etc.

Here are some quotes from the Getrag Company Powershift Information Manual describing what is happening in the centre console

A toothed disk integral to the detent plate engages with a toothed wheel that rotates a magnetic wheel. This magnetic wheel excites hall effect sensors in the Transmission Range sensor to provide the P/R/N/D position signal to the TCM.
The gear selector assembly positioned in the center console is mechanically connected to the transmission by
a cable which is used ONLY to engage and disengage the Park gear.
It does NOT move a manual valve in the valve body for there is not a manual valve to move.
The shaft inside the transmission which the gear selector lever rotates to engage and disengage park has a detent plate with a toothed disk that rotates a range sensor integral to the TCM. This provides a direct P/R/N/D signal into the TCM.
The transmission range sensor (TRS) is directly connected to the TCM providing the signal it needs to know if the selector lever is placed into Park, Reverse, Neutral or Drive. This sensor contains a wheel with magnets strategically located around approximately half the wheel to excite hall effect sensors with which its position can be determined.

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#7 TheAntman

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Posted 19 October 2020 - 06:34 PM

I've noticed that Mk4 Mondeo's are somewhat prone to corrosion on terminals. I noticed the passenger side reversing light on my car wasn't working and, on removing the bulb holder, noted how badly corroded the terminals are.

Tried cleaning them up, but really I should replace it - but it would seem that this is a common problem as I haven't seen any used ones for sale anywhere.

I have managed to get mine working though.

I'd suggest this as a staring point. Rule out the obvious first.

Check the bulbs and the terminals.

Then I'd put a multimeter on the connectors at the lamps to check that there is a supply voltage when Reverse is selected.



#8 Speedlimit

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Posted 19 October 2020 - 10:42 PM

Reading the test procedure both the GEM and TCM should produce a 'backup lamp request signal' I guess that would start with the TRS as TrevorB mentions above.

 

A multimeter test is described to exclude the GEM.


Edited by Speedlimit, 19 October 2020 - 10:53 PM.


#9 Speedlimit

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Posted 19 October 2020 - 11:15 PM

After the usual bulb, fuse and connection checks:

Find out whether the vehicle is fitted with an automatic transmission. If so:

Check whether a backup lamp request signal is given by the GEM.

If YES, disconnect the left-hand tailgate lamp assembly connector and measure the resistance between pin 2 wiring harness side and ground.


If the resistance is less than 2 Ohms, install a new GEM.
If not, check the circuit....


If NO, check whether the TCM requests a backup signal...

At this point I think there's a misprint with YES and NO,
anyway it only makes sense if I swap them round to mean
if YES check the auto transmission if NO, check and replace if necessary the TCM.

 

 

I hope that's right, just paraphrasing the manual.





 


Edited by Speedlimit, 19 October 2020 - 11:18 PM.





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