W124 mysterious abs and no tach

[mabbs]

Hi,

First foray into diagnostics for me on a Benz. Two problems:
1. Abs light illuminates on reverse, yet 90 % of the time self tests fine and goes off when going forward;

2. Tach' non function all of the time.

I read that the OVP relay is problematic on these vintage Mercs, would this be a good place to start and, if so, what am I looking for? Would it be worth measuring resistance of abs sensors before this?

Rich

W124 300d, 136k - 1990

 

[grober]

my guess and its only a guess is that the ABS circuitry is sensitive to voltage levels which are dropping when you select reverse. If you had some sort of short in the reversing light circuit that might produce enough current drain to drop the voltage below the alarm threshold. The other weird thing that can happen is if your front wheel bearings are loose then in reverse the sensors may come up with errors due to angle changes in clearance on the toothed wheels. The OVP is worth checking also.

 

[Dieselman]

Not sure about this but isn't the rev counter amplifier under the diagnostics cap..? I'm sure I've heard of them making bad connections .

 

[sehmbi]

OVP Location

My ABS light has come on, the garage found rear pads worm and replaced but the ABS still permanently on, Where is OVP relay located on my W124 T230TE 92.
PS poor starting after 30 seconds all ok.

 

[nick mercedes]

My ABS light has come on, the garage found rear pads worm and replaced but the ABS still permanently on, Where is OVP relay located on my W124 T230TE 92.
PS poor starting after 30 seconds all ok.

OVP on left flitch, near to battery.

 

[sehmbi]

Found the OVP relay, Removed fuse and started the car still the same, Cleaned and put back the fuse still the same. The ABS light on and poor starting and smokee. Is there any more tests to made before i go and buy the OVP.

 

[sehmbi]

Fitted New OVP Relay No ABS light and starting 1st time, So the test is run it without fuse if same as B4 must be the relay (checking fuse 1st).Thanks guys for your help, Only cost £44.00 from Euro parts.