how do you test an OVP to check if it's working?

jrmd01 · #1 09-11-2002, 04:04 AM

I think the OVP is not working on my 86 300E. But before I go out and spend $50-100 on a new one, how do I test the OVP?

mbdoc · #2 09-11-2002, 08:10 AM

Does your ABS light stay on? IF not then the OVPR is working, however they can lose power at times & then you can have hard starting when the engine is cold.

stevebfl · #3 09-11-2002, 08:29 AM

For test purposes the OVP acts like a fuse and tests like one. Power in and power out. thats all it does. Since it is rather hard to test at the ends of this fuse, it is usually easier to see if the devices powered are powered. ABS as Doc pointed out tells one part of the circuit. The KE controller is another. The easiest way to tell if it is powered is to evaluate EHA current or duty cycle codes. Look at the DIY article for evaluating engine controls to see how to do this.

All the answers to OVP can be seen with either ABS, EHA, or idle speed current. Although the most common faults knock out all of the above. I have seen every circuit fail separately and differently (more than one type of symptom).

jrmd01 · #4 09-11-2002, 01:14 PM

The OVP seems to be working intermittently in my car.

After starting my car, the ABS light would remain on sometimes 5-15min other times the whole duration of the drive.

When the ABS light stays on, the car idles very rough. After looking at various post about the ABS light, I suspect my OVP is faulty.

I've tried cleaning out the OVP connection points, but the problem persist intermittently.

What do you guys think? Should I just spend the $50-100 and get a new OVP?

JR

Cap'n Carageous · #5 09-11-2002, 01:28 PM

Benzwood had one for sale for $20 not long ago.

stevebfl · #6 09-11-2002, 02:18 PM

If the date code is over tens years old I would definitely replace it from a maintenance concept. The intermittant problems can not be tested for near that cheap.

Mick J · #7 09-11-2002, 02:44 PM

I fixed the one on my '89 230TE as follows.

Open up the aluminium casing by releasing the locking tangs and carefully remove the printed circuit board inside. With a hot soldering iron carefully melt each joint on the pcb and allow to cool again.

Replace the pcb and secure inside the casing by carefully bending the tangs back in.

Provided you are carefull and know what you are doing with electronics there is nothing to loose, never saw that ABS light again (except during ignition on self test) for the 3 years I had the car after that. Before it used to come on and off almost at random, always associated with poor idling and reluctant starting.

#8 09-22-2002, 06:38 PM

I have had the same intermittant problem with the ABS light on my '86 300E. I also have been having a problem with the dash light fuse (3) blowing out, and/or the dash lights noit working. Could this be related? I think I will change out the OVp as a preventitive measure...

Thanks,

Kevin

jrmd01 · #9 09-24-2002, 01:38 PM

I changed my OVP the other day. I paid $58 for the OVP relay and installed it myself. I don't have anymore problems with the ABS light turning on and the car runs and starts fine.

In response to one of the replies about the dash lights...I don't think your OVP has anything to do with your dash lights not comming on, although don't quote me on that cause it's just my thoughs/opinion. My dash lights no longer turns on either. I suspect I have a grounding problem because now the whole right side of my instrument pannel don't work (the RPM guage, the clock, and the dash light). It stop working when I had the instrument pannel pulled out to change the light bulb. I should have just left it alone, did more damage trying to fix a $1 light bulb....damn I regret it. (I haven't fixed the NEW problem because of fears of doing more damage than good)

jrmd01@yahoo.com

xp190 · #10 01-11-2003, 02:59 PM

I just the the resoldering of the OVP, much more affordable then getting a new one, the only parts in it are two resistors, and a switch, provided the switch works, you can get the other two parts for $0.05 each at any electronics store. So I guess you pay for the logo, and aluminum casing, sheesh what a rip off.

xp

stevebfl · #11 01-11-2003, 03:20 PM

I just hate it when people that haven't a clue spout rip-off. There is a whole lot more in an OVP than a couple resistors. I only know this because I know what it does and how. It uses a zener diode to shunt all voltage over say 16v to ground.

I haven't a clue how much a zener diode is but if you don't like MBs price try cramming a PC UPS under your hood recalibrated to 12v systems. Its just a smart fuse, damn it.

xp190 · #12 01-12-2003, 10:14 AM

a zener diode is $30

anyway stevebfl not to get on your nerves or anything, but this is what I did since I can't always afford to buy all brand new parts, so I keep it to a minimal cost, I am a student and I do have hefty tiution fees as it is.

xp

stevebfl · #13 01-12-2003, 11:09 AM

Ahhh.... $30 not quite so much a rip-off as a few .05 parts.

No problem with fixing the part, I fix various electronic components every day for people, mostly by resoldering PC boards. The economics vary with every case and there has been many a time that after fixing a part to solve a diagnosis I have then replaced the part to assure the fix. Many a customer would be upset at a further failure. Risk depends on the customer and their finances and in some cases age, ability to manage, and security issues.

Arthur Dalton · #14 01-12-2003, 11:56 AM

<<>

Only when the Government is buying them.....

xp190 · #15 01-12-2003, 11:56 AM

I have no problems in fixing my own parts, as long as it's a simple part. I had to do the same with my cruise control computer cause it would not work, but that part is quite expencive to replace, it works now, and works well, just need the righ tlight bulbs now cause one went out.

I'm hoping one day I'll be able to fix all such parts, but not just for myself.

xp

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