w124 722.5 has lost 5th gear

[millo777]

My w124 has lost its 5th gear, and the cruise control has also stopped working (Not bothered by the cruise control, but they may be connected).

I've removed the micro switch from the gear shifter and it appears to be working. Continuity tests ok between the 2 pins, and continuity breaks when the switch is depressed.

Could it still be the switch at fault? is it worth replacing just in case?

What else should I be checking?

The tranny fluid is long overdue a change, but I'm holding back in case there is something to investigate (Valve body??) while the tranny pan is off.

Any help much appreciated.

 

[Charles Morgan]

Similar issue in mine was caused by failure of rear ABS sensor which doubles as a speed sensor for selecting 5th and for cruise control.

 

[millo777]

Thanks for that. Not something I would have thought of checking. I'll investigate further.

 

[millo777]

Did you get an abs warning light before the sensor was changed?

 

[Charles Morgan]

Can't recall I'm afraid.

 

[WDB124066]

Also try reading the codes and clearing them, sometimes a sticky solenoid in the trans will throw a code, clearing the code may get it functioning again. Dirty trans fluid can [I guess] contribute to this problem so after a change it may behave itself for a while.

How many miles on the trans & fluid do you know...??

 

[millo777]

The trans fluid is long overdue a change. I have the filter, gasket and fluid ready along with new drain plugs and washers for the pan and torque convertor.

I'm reluctant to do the job until all other investigations have been done to avoid doing it twice if the drain pan needs to be dropped to check anything.

Charles suggestion of the rear abs sensor makes sense as the cruise control is also out, but I don't have an abs light on the dash.

Anyway...I've totally forgotten how to read and reset codes on these (The star system on my w140 is a god send). I seem to remember being able to do it using a multimeter?

 

[hotrodder]

I would've thought manky/ancient ATF etc would affect more than just 5th which is more akin to a leccy operated overdrive. AIUI problems with the 4-5-4 shift are virtually always leccy related with these... as said speed sensors are a prime suspect if cc was lost at a similar time. Won't necessarily trigger an ABS fault kinda like a dodgy brake pedal switch can take out cc but leave the brake lights functional. Dunno if the brake pedal switch would effect 5th gear or (more likely?) non functioning cc could as both rely on inputs from similar systems including the throttle

Not much specific to trouble shooting 5th but FWIW http://www.w124performance.com/docs/mb/other/tranny_722_Mitchell.pdf and cruise control is covered under section 30 here Mercedes Benz Model 124 - M104 Maintenance Manuals
http://www.w124performance.com/docs/mb/diagnostics/DTC_List_W124_M104.pdf is a list of fault codes and (briefly) mentions at least some of the ways of reading them. There's various pics/diagrams for home made blink code readers scattered around the internet

 

[WDB124066]

A sticky solenoid will throw a code or at least it did on mine, once reset it was fine for a good 15 000 kms until I replaced the whole trans.

 

[ray_hennig]

My w124 has lost its 5th gear, and the cruise control has also stopped working (Not bothered by the cruise control, but they may be connected).

I've removed the micro switch from the gear shifter and it appears to be working. Continuity tests ok between the 2 pins, and continuity breaks when the switch is depressed.

Could it still be the switch at fault? is it worth replacing just in case?

What else should I be checking?

The tranny fluid is long overdue a change, but I'm holding back in case there is something to investigate (Valve body??) while the tranny pan is off.

Any help much appreciated.

Not the same symptoms as mine but I would strongly recommend clearing fault codes first.

Any difference?

If so, change the 4/5th microswitch; it's only £20 ish.

If better, certainly do the fluid/filter change and ensure the torque converter (separate drain plug) is drained.

Bonne chance.

RayH

 

[millo777]

Thanks all, I'll nip to Maplin tomorrow to get the parts for a code reader. My car has pin 13 connected, so there could well be some codes stored. Clearing the codes sounds like a good first step to take.

 

[del320]

18 months ago, loss of fifth gear - or at least, the inability to change up - was the first symptom that the loom was on the way out.

I presume yours has been replaced?

(here)

 

[bolide]

If cruise has failed I'd check the speed signal first

The speed signal comes from the back of the speedo via a Hall Effect sensor plugged in next to the speedo cable. The speed signal is used for cruise and for some satnavs. It's available in the footwell on a green / yellow wire

On some cars the speed signal is fed via an otherwise unused pin on the OVP relay. I had one car where 5th disappeared after the socket dropped out of the base - normal service was resumed after the problem was located & solved

A clued-up main dealer will have a wiring diagram showing all the wiring joins & earth points - these are good places to look for bad connections

Replacing the microswitch is a great idea if it's faulty, but fixing electrical issues by guesswork is generally not productive

Cruise has its own ECU, as does the gearbox, so the chances of them both failing at the same time, without there being a common cause, are slim

Nick Froome

 

[millo777]

Having built a code reader, I was getting code 9 from pin 14, and code 28 from pin 8, both relating to VSS (Vehicle speed sensor), but curiously nothing from pin 13 (Transmission electronics).

After a bit of playing around with a multimeter, it turned out the VSS lead that fed the radio (Yellow and green for ref) has not properly terminated, probably from when the original radio was replaced. A terminating crimp and some insulating tape later, and 5th gear and cruise control have resumed service.

Thanks to everybody who posted, and especially Bolide for the invaluable info.

 

[Wlimorsi]

This thread is old I know but I am facing the same problem. I have a S124 too with the same problem you had. No cruise control, no 5th gear (unless I unplug TCM then it goes 3 -> 5) as well as ABS light.

I have the same codes 28 from pin 8 and code 9 from pin 14. It STILL had ABS light on even after clearing the codes and the codes come back after a drive.

Did you have the ABS light on too when that happened?

 

[802235273]

Hi

Car is 1995 E320 with the 722.5 auto box but 5th gear is not working.

I have what appears to be a missing VSS as Socket 13 is reporting code 6. I also cant seem to erase the code to see if 5th gear starts working.

I have changed the Hall effect sensor and swapped the HGS module but still no 5th gear.

Does the VSS definitely come from the sensor behind the cluster as I have read it can also come from a wheel speed sensor.

I have no wiring diagrams so if any one can point me in the direction of where I can get them that would really help.

I would welcome any ideas.

TIA