If it shows no cont. both ways [ polarity wise], it is open.
If so , go to RS and get one [ for about 20 cents] and solder it in there , and go give it a try..

Edit:
Make sure of polarity of the new one . This is what the little stripe on one end of the diode is there for . Put new the same position [polarity] as the one you take out...

Electronics 101 question: No continuity but will pass current? How can that be? I'm lost here unless that means there is a "gate" in there that closes upon current application. By the way, the ID of the whatyoumaycallit in 1N 4003.

Well I did pull the OVP relay fuse on my HFM equipped E220 and guess what? No change to the engine, it started and ran fine, idle speed compensation worked in the normal way, only difference was the ABS light was on.

So I conclude that the HFM engine management computer is not fed from the OVP relay, presumably it has it's own protection from high system voltage.

__________________
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)

Best discussion on electronics I've come across here in a LONG time. So, allow me to toss in a couple questions for the pros:

1 -- Get out on the Interstate and hit the brakes at speeds in excess of 70MPH in my SL. I get a slight pull to the right front and the ABS light comes on. After that it brakes w/o any pull. Turn the ignition off and the ABS light goes off. Got an ABS computer problem you think?

2 -- Just replaced the Environmental Control Unit (000 822 1203)awhile back ( a $1,500.00 part through Fast Lane and the MB dealership). Managed to find one on the internet for $125.00 so felt much better about doing it. Installed it and it worked fine for about six weeks. Now when I turn the A/C on and pull up to a stop light, the ECU makes a bzzzttt noise, the RPMs surge about 300RPM. You can put your hand on the ECU and feel this is where the relay(?) is sticking. So, the questions are: (1) what's causing me to continue to have this problem with the ECU, and (2) what's the connection between the ECU and the RPM surge? I'd think the latter would be more an idle control valve/unit problem and don't understand what's going on here.

FYI, I replaced the OVP at the same time I replaced the ECU. I've also replaced the idle control valve and idle control unit.

Any assistance here will be GREATLY appreciated.

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

[QUOTE]Originally posted by sublettd
[


2 -- Just replaced the Environmental Control Unit (000 822 1203)]



What the heck is an environmental control unit? I hope I ain't got one!! If so it too will fail or already has!

<
the whozeejigger 4003 is a common generic diode.

Common Diodes allow current to conduct in one direction and restrict flow in the other. That is why the polarity test -- low resistance in one direction, high in the other.
So if one were to put a diode in a dc series circuit, it would conduct in one direction, but if you flipped the leads over, it would not.
Kind of a one way valve in the plumbing world..[ which is a good way to visualize / compare electon flow]

They are commonly used to rectify a/c current into DC current, but have many other applications...

Cap,

The ECU is a "little black box" that mounts on the firewall behind the glove box on my SL. It has two plugs which go into it, one with 12 wires and the other with 4. It controls--so far as I know--the heating and A/C for the vehicle. May control more than that as well (witness my RPM surge when stopped).

My guess is you have one and I hope you never have to replace it. FYI, when I first started looking into the problem the MB dealership here showed a price of about $254.00 for the unit. When I went back to order it, the price had jumped dramatically. That's when I started looking in other places. My guess is their bench stock on the unit(s) is getting seriously low. Same thing happened to the 000 822 0403. It's now over $1,100 at the dealership.

Going to drive a Mercedes you're going to pay the price, or so it seems!

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

It's like a vendor told me once," how can you look someone in the the eye and tell them a distributor cap costs $135?" And you know something else?? In my county a tag and insurance for a fourteen year old Mercedes is as expensive as a three year old anything else!!!

Wait a minute, It seems I'm losing my bias! I'm a BENZ owner!! I should pay more!!

Sublettd, Check your tyres and inflation pressures. Your pulling problem may be related to different rolling radius of the wheels on each side and the ABS is interpreting this as wheels rotating at different speeds. It thinks this is wrong so shuts itself down.

I have heard of this happening before when someone replaced a tyre on one side only and left the part worn one on the other.

__________________
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)

Cap,

The parts guy told me, "I don't price 'em; I just sell 'em". I'm sure he catches more grief than the average person and is glad to go home at the end of the day. Paid $8k for the car and have put another $5k into it. Just about to get it where it ought to be.

Mick,

Usually keep the tire pressure where it's supposed to be, but will check as you suggest. That's an easy enough fix, but I doubt that's it. Why? Because it doesn't cost enough! I'm starting to get as calloused as Cap. ha!

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

Looking for shorts in the wiring, I just noticed that there is no connector or wire in the OVP plug for terminal 30a. Is that correct?? The terminal connects to nothing??

After reseaching the service CD, it looks as though pin 30a is only used on the California version. I'm not sure of it's function though.

Came across some info in a UK MBZ magazine that provides a relatively simple test for an OVP relay that I haven't seen mentioned anywhere else. Did post this info against a recent OVP thread, but was requested to also add it here in-case someone picks this up in a search:

The article is in the Dec '04 issue of MBZ Club magazine here in the UK written by Jeremy Stevens. It states:

"Test 1: Connect pin 30 to a +ve 12v supply and pin 31 to the -ve. Under this condition the only output should be on pin 30a.

Test 2: In addition, now connect pin 15 to the +ve and both relays should operate with supply voltage now also appearing on both pin 87E and 87L (so all pins 'live')".

On my good OVP relay I noted that there was an audible 'click' as power is added to pin 15.

My understanding is this is a fairly basic test: one up from checking the fuses are intact; that it doesn't rattle when you shake it; and that there's no cr@p around the pin connections.

If it fails this test you are pretty sure the OVP needs replacing, if it passes it though, there is still the possibility of an intermittent fault caused by something like a weak solder joint.....

My car is having intermittent fuel delivery problems.

Drives fine, some time hesitates, other times stales, then after waiting - it runs fine again.

Seems consistent with things I've read about OVP (Over Voltage Protection).

Where is the OVP located, so I may visually review it's condition?

Thanks.

__________________
Thanks for the help
Bill Fisher

'86 560SL (186K) - Now a 'classic' : Registered as an Historic Vehicle
02 E430 in the stable
'14 LS460 (Lexus)
- - - - -
'95 E420 (198K) found a new home
'99 E320 (80K) (gave it's life for me as we hit a bumper)
'95 E420 (231K) Sold to a happy buyer, new to Mercedes
'90 300E (65K) Sold to an Mercedes Lover
'92 190E (215K) - retired to the salvage yard
'93 500SEL (214K) - Moved to another family, still runs like a young pup

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