w124 Coupe front seats not locking back down.

[cerbera84]

Hello, just picked my car up after being Mot and the fronts seat backs no longer lock in place when the ignition is turned on. I don't know if it's related but I had the rear passenger side electric windows mechanism replaced, so I don't know if something could have been dislodged when the door card and rear seat was removed. I had a quick look under the seat but there was nothing obvious. There also used to be an audible hiss from behind the dash when the ignition was turn on, which is no longer there.

Cheers

Chris

 

[tintinmt]

Have you tried checking with the engine running? I believe the lock may be generated by the vacuum pump.
Also, the car should fail MOT if the seats don't lock.

 

[WDB124066]

May be they put the front seat/s right forward to get better access to the rear, at full forward then back to normal may cause the vacuum hose, [from the floor to the seat at the front bolt To under the cushion centre, forward], to come lose. A mirror and torch can help to trace the vacuum lines and the Y connector under the front of the seat.

 

[Philbask]

The vac pump I believe is under one of the back seat squabs (nearside I think?) If it's this side you have had work on, worth checking nothing has been dislodged. 2 minute job, the squab is removed with the red catch under the front of it, the pump is surrounded / protected by foam packing.

 

[dinoy]

the seats should be locked only when door is closed, or it is locked even when door is open and button used to release the seat??

 

[grober]

The vacuum is produced via the engine manifold [ thus the engine must be running] This vacuum operates 1. the head light leveling [ probably the hissing under the dash??] 2. the heater vacuum actuators and 3. the seat back locking mechanism. You will almost certainly have sprung a leak somewhere in the system meaning there is insufficient vacuum somewhere. If the front door/s is open the vacuum to the seat back is disabled IRRC. The vacuum pump under the rear seat operates the central locking rear headrests and locking petrol cap.

 

[cerbera84]

The vacuum is produced via the engine manifold [ thus the engine must be running] This vacuum operates 1. the head light leveling [ probably the hissing under the dash??] 2. the heater vacuum actuators and 3. the seat back locking mechanism. You will almost certainly have sprung a leak somewhere in the system meaning there is insufficient vacuum somewhere. If the front door/s is open the vacuum to the seat back is disabled IRRC. The vacuum pump under the rear seat operates the central locking rear headrests and locking petrol cap.

Thanks I had both doors shut, the engine running and the seats didn't lock. If when he replaced the electric window mechanism he had the front seat right forward could that have dislodged a pipe connection? If one of the pipes under the passenger front seat had been dislodged would that cause both seats to not lock?

 

[grober]

You need to get down and dirty and find the vacuum piping below the seats. There will a flexible rubber connection there. Undo this to see if you have a vacuum. After that its a case of back tracking along the pipe work till you find a vacuum present. Any break/ leak in the pipe work anywhere between the seat and the manifold will result in a loss of vaccuum. [ to answer your question- yes a leak on one seat would cause both seats locks to fail to operate] It may be that a leak on one of the other systems I mentioned is causing this leakage- until this is "plugged" you may not have sufficient vacuum. You just have to be methodical and check all the pipework.

 

[WDB124066]

There is a vacuum connection at the front of the front seat just behind one of the seat/floor bolts, from there it goes in a big loop under the chair. Should have good vacuum at the Y connector at idle.

Otherwise...

Mityvac

 

[cerbera84]

Success!!! The Y pipe under the drivers seat had become disconnected to the black module. Reconnected and now it works perfectly. Glad it was an easy fix as it was really annoying, and didn't feel overly safe.

 

[dinoy]

Success!!! The Y pipe under the drivers seat had become disconnected to the black module. Reconnected and now it works perfectly. Glad it was an easy fix as it was really annoying, and didn't feel overly safe.

so it locks with ignition on (is the gearbox in park or engaged), does it lock without ignition on