W124 230E 1992 ABS LIGHT ON AND POOR COLD STARTING

[W140s500]

I wonder if I could have a few ideas on this recent niggle I have encountered - first problem in 5 years !

Went to move the car last week and it was not happy trying to start; jump leads were used and it started, but didn't want to rev until warmed up and would die if the throttle was touched. Once up to operating temperature runs as normal and electric fan clutch does work also so all seemed normal .

ABS light illuminated as normal when ignition switched on but does not extinguish.

OVP relay inspected ( no obvious fault ) and also tried another supplied by w140 spares - no different
Battery charging at 14.3 volts
Front ABS sensors visually inspected and cleaned
Both relays on ABS unit swapped from a substitute vehicle - no difference
No obvious harness issue on visual glancing
ABS and engine ECU behind battery visual inspection of terminals - all clean
Recent new plugs, cap, leads and rotor
No misfiring

With an assistant whilst turning the ignition on and off the assistant said they didn't feel any clicking or pulsing from the ABS unit which they did detect when inspecting a similar vehicle which was used to ' borrow ' the relays under the plastic cover.

Have I missed something painfully obvious ? ABS worries me more than the cold start issue which could be the cold start device but seems strange I have 2 issues arrive at the same time

 

[SMS]

I wonder if I could have a few ideas on this recent niggle I have encountered - first problem in 5 years !

Went to move the car last week and it was not happy trying to start; jump leads were used and it started, but didn't want to rev until warmed up and would die if the throttle was touched. Once up to operating temperature runs as normal and electric fan clutch does work also so all seemed normal .

ABS light illuminated as normal when ignition switched on but does not extinguish.

OVP relay inspected ( no obvious fault ) and also tried another supplied by w140 spares - no different
Battery charging at 14.3 volts
Front ABS sensors visually inspected and cleaned
Both relays on ABS unit swapped from a substitute vehicle - no difference
No obvious harness issue on visual glancing
ABS and engine ECU behind battery visual inspection of terminals - all clean
Recent new plugs, cap, leads and rotor
No misfiring

With an assistant whilst turning the ignition on and off the assistant said they didn't feel any clicking or pulsing from the ABS unit which they did detect when inspecting a similar vehicle which was used to ' borrow ' the relays under the plastic cover.

Have I missed something painfully obvious ? ABS worries me more than the cold start issue which could be the cold start device but seems strange I have 2 issues arrive at the same time

Check the voltage protection relay fuse, next to battery.

 

[W140s500]

Yes, single 10 amp fuse was fine on the protection relay plus even tried a substitute protection relay and sadly no luck; that was my first thought but sadly not the case

Been checking earth and other cable connections tonight for cleanliness, double checked the air idle valve and hoses etc and everything ' seems ' good. If I take the silver relay out from beneath the plastic cover on the ABS unit the light is deactivated, so there is some life working somewhere but as yet to find the gremlin which is playing games with this otherwise well behaved motor

 

[SMS]

It definitely sounds like you have a problem with the output from the ovp relay, sometimes a plug falls out of the ovp relay terminal block.

 

[W140s500]

The multiplug which presses onto the base of the ovp relay all looked clean at a glance, but I will have to have a closer examination to see if anything isn't correct.

I dislike electrical gremlins the most !

All help and suggestions given are gratefully received

 

[W140s500]

I last night had a closer inspection of all visible cables and connections; everything looks fine yet it still has the ABS light permanently on and still is bad at cold starting.

I did however notice a humming noise from the passenger footwell. I know there is a little fan behind the dashboard on these but it sounds more than just a fan. I believe the alarm system components are in that area.

Daft question,but has there ever been a case of those components throwing a spanner into the works ?

Eventually I will resolve this * fingers crossed *

 

[W140s500]

FIXED

Bought a new OVP relay and problem solved

Lesson learned - don't trust/assume a used electrical part is good unless you have tested and removed it yourself; just unfortunate I was sold a faulty one, but these things happen from time to time

On the plus side, I have been cleaning and improving a few other things so not a complete waste of time.