AM6 auto tranny not going into Neutral State when stopped

[AlvinCitroenC5]

Hi all,

After purchasing a used 2005 Citroen C5 II 3.0 V6, I have almost fixed all the mechanical issues with the car, with the exception to the function where the AM6 TC-80 6 speed tranny have a feature that goes into neutral when the vehicle is stopped and the brake is applied. While my car idle at the stop light with the tranny in D, the engine idle, the tranny / torque convertor really wants to drive the car forward, thus, applying more brake pressure to hold still the vehicle will cause the engine to vibrate.

From a reply from another post, members on this forum confirms that the transmission automatically goes into neutral when the vehicle is fully stopped, in D, and brakes applied. And I have a P1536 fault code from Lexia. I was also told by a member on this forum that there is two sensors at the brake switch, one which tells the brake light to come on and release the gear lock while in P, while another one sends a signal to the automatic transmission. However, I cannot see that there are two contact switches on top of the brake pedal mount. So, for now, I have to manually place the transmission in N when at the stop light to feel comfortable. I hope that some of you can enlighten me on how to remedy this problem. Thank you all.

[GiveMeABreak]

This is the Toe Board Assembly showing the brake switch - number 10 and is part number 4534 65

C5 II Toe Board Assembly

[Hell Razor5543]

It is possible that that switch is actually TWO switches in one housing. My C5 Mk1 now has cruise control, but I had to check the brake pedal assembly for the relevant switches. One of the options was for two independent switches (each with a pair of wires), the other was for a single switch, but with four wires going into it. Mine had the latter option.

[AlvinCitroenC5]

Hi,

Firstly, thank you for your help. I manage to obtain a new switch and after installing it the transmission now does go into neutral state after about 1 sec while holding the brakes at the stop like while the transmission is in D. The result is a much better idle. However, when I let go the brake pedal or place the gear level in Manual mode, the transmission goes out of the neutral state, and while continue holding the car with the brake, the engine shakes again. Thus leading me to think that there is something wrong with the torque convertor. The person who had this car had some butcher mechanic in China to fix it, as my mechanic and I have slowly taken parts off the car to inspect, and find that many things has been removed but not installed properly.

I have already flushed / changed the transmission fluid out once, and although I have not purchased a mechanically sound C5, I will continue to repair it, since there are less than 100 of these C5 running in the whole China. I wonder if you would recommend me to do at this point in time? Replace the torque convertor? Reflush the transmission fluid? Remove the solenoid / valve body for cleaning and inspection? The transmission do shift well, but I can feel that in manual mode downshifting from 4th to 3rd is a little rough. But it has since gotten better with driving the car more after replacing the transmission fluid once.

Thank you.

[Hell Razor5543]

What is the mileage?

[AlvinCitroenC5]

165K Km.

[AlvinCitroenC5]

Hi,

To provide and update: I switch the transmission to "Snow / Winter" mode, and the car feel a lot smoother when I am in "D" while holding the car still at the stop light.

[lexi]

The solenoids on that box can be checked with a multimeter for resistance values while still in place. You will have to search for the data, as I no longer have the workshop manual for that box.

[AlvinCitroenC5]

Thank you for your suggestion, but can you provide more clarity to what you have suggested? Are you trying to say that one or more solenoids within the valve body can cause the torque convertor or transmission to "drag" the car forward / reduce the stall speed to the point where the engine shudders while in D while "neutral mode" is not engage while using the brake to hold still the car while the gear lever is in "D" or manual mode? Thank you

[lexi]

Thank you for your suggestion, but can you provide more clarity to what you have suggested? Are you trying to say that one or more solenoids within the valve body can cause the torque convertor or transmission to "drag" the car forward / reduce the stall speed to the point where the engine shudders while in D while "neutral mode" is not engage while using the brake to hold still the car while the gear lever is in "D" or manual mode? Thank you

I cannot remember if any of these solenoids affect that problem with your car. You would need to get workshop manual to see what each of their purpose and function actually is. The manual will show you the resistance values of each solenoid. My suggestion was that you can check them in place, without removal.