9 pin Diagnostic Plug

[38Kestrel]

Hi, My 300CE from 1991 has a round 9 pin diagnostic socket. My Independent Merc maintainer does not have this plug type on his system. He says they were only fitted for a short time and I guess he thinks he will never get asked again as car is almost a classic now. Can anyone help with data on this. Are there adaptors? is self diagnosis possible e.g. "count the blinks"? Can a cable be bought if so from where and how much? I could go on to describe the problem. but not just now.

 

[television]

You can do a google search and this will come up, yes you can use a LED tester and read the faults out, the info is here on this site if you do a search.

You can make your own probe, very simple, but I am out of time today. Welcome to the forum.

 

[38Kestrel]

Thanks for the quick reply. I've been looking up Google but not really come up with the answer. Its late. Will log in again tomorrow.

Thanks Geoff

 

[jibcl500]

Can you put apicture up of the diag socket ?
I might be able to help depending on where you are.
jib

 

[38Kestrel]

Picture of 1991 300CE '9' pin diagnostic socket

Jib, Thanks for the reply I am in Grange over Sands 20 mins from J36 of M6.
Here is a pic of the elusive socket. If there is any way you can help, that would be a great into to the forum. Best regards, Geoff

 

[jibcl500]

those three holes in a straight line at the top do they have a number next to them or a colour code red, yellow, black.

I have a connector which is three plugs.


jib

 

[ant500sl]

To read the output from this connector you need a multimeter that has a setting for duty cycle/dwell or frequency. Plug number three on this connector is the output for the ecu which has a fairly basic self diagnosis routine. The negative cable of the meter should be attached to a good earth and the positive placed in plug nuber three.

The result is a readout in % which can then be looked up in a fault table.

If you have the right equipment I can run through the process in detail and explain any codes.

Nice clean car by the way!

 

[38Kestrel]

Pin numbers

Jib,
The pin outs (females in the socket) are numbers 1,2,3,4,5,6 then 7,8,9. These last being the top ones you mention, they look straight in the pic, but I think they are all in a circle. Thanks for the help.

ant500sl
I think you are looking at Jib's car in the pic. Mine is tidy, lovely cream leather interior too, but smoke silver. Thanks for the offer on codes, will need to borrow stuff I think. Watch this space.

Cheers, Geoff

 

[C220GJS]

Your connector is shown on P13 in this link;http://www.benzworld.org/forums/att...55-diagnostics-sl-pre-94-diagnostic-codes.pdf.
Hope this is of some help.

 

[ant500sl]

You can pick up a cheap multimeter these days for a tenner that will do the job.

By the way I was referring to your car, not many 16 year old cars have an inner wing that clean!

 

[38Kestrel]

Thanks for the complement

Yes, the car is very clean, inside and out, and virtually zero rust. Just a rather weathered bonnet. It had been valeted before I bought her at Auction in April, but I have been underneath and even there its pretty good. Had an easy life in its earlier years - see my thread in the "members cars" list by the way. It has 122,000 now though.

Thanks for the offer of detail, I will source an appropriate meter, so any info you have would be much appreciated.

Many thanks, Geoff

 

[star]

Hi, My 300CE from 1991 has a round 9 pin diagnostic socket. My Independent Merc maintainer does not have this plug type on his system. He says they were only fitted for a short time and I guess he thinks he will never get asked again as car is almost a classic now. Can anyone help with data on this. Are there adaptors? is self diagnosis possible e.g. "count the blinks"? Can a cable be bought if so from where and how much? I could go on to describe the problem. but not just now.

This plug connect directly to a bosch scope with the right leads, saves you connecting to the coil for timing etc, the mixture can be read on catalist vehicles via pin 3.

 

[38Kestrel]

To read the output from this connector you need a multimeter that has a setting for duty cycle/dwell or frequency. Plug number three on this connector is the output for the ecu which has a fairly basic self diagnosis routine. The negative cable of the meter should be attached to a good earth and the positive placed in plug nuber three.

The result is a readout in % which can then be looked up in a fault table.

If you have the right equipment I can run through the process in detail and explain any codes.

Nice clean car by the way!

Ant500sl
Hi, I now have a decent multimeter with dwell/dutycycle readout. If this will suffice, I would be most obliged for the test details and fault codes.

My particular problem is that the engine won't tickover without the throttle open (but only when its hot) its a pain, but doesn't stop me using the car. If I can spot a sensor failure for example that would be excellent. I can see from the posts that these sorts of problems can be tricky to isolate.

Thanks in anticipation.
Geoff

 

[Legoman]

id be interested in this thread too , especially the diagnostic codes

 

[ant500sl]

I'll start with the initial procedure which is quite straightforward.

Ignition should be on but do not start the engine, set multimeter to duty cycle and connect earth lead to a good earth point and the positive lead to plug number 3 in the 9 pin connector. If the system incorporates diagnostics you should see a reading of 70% or possibly 30% depending on how the meter functions. This is the code for a fault in the crankshaft sensor, as the engine is not running no signal is produced and the module assumes a failure.

Next start the engine and see what happens to the reading, normal for non cat cars is 50% and for cat cars the reading should fluctuate. If you get a fixed number then this indicates the fault.

This function does not have a memory and will only show up codes while the engine is running. If you have a code or other odd result I will describe the next steps as required.

You may also see a square diagnostic socket on the bulkhead which can also be accessed but the 9 pin socket is the best place to start.

 

[38Kestrel]

The first test results

Ant500SL

I've been away hence the delay.

What I find on pin 3 is this...

From cold.
Ign ON - 68.4%.
Tickover - 48.4% for ~15 seconds then a steady rising signal halting at 90%.
2500rpm - signal falls to say 82% moving about with revs to some extent.
Lift off - signal drops instantly to about 50% before steady rise to 90%.
At all times tickover is a bit "lumpy".
Plug leads & distrib cap were replaced in May along with all the fluids.

After 30 minutes driving to warm up, car starts as normal with similar readings to the above.

After further 30 minutes to cool, ditto.
So today is a good day!?! She won't show the fault, which would normally prevent tickover on a hot start (without using the throttle).
Will try again tomorrow.

p.s. I have rigged up a lead so the meter will show while driving. Is there any other useful data available on the 9 pin?

Thanks for the help so far, Geoff

 

[ant500sl]

The first reading of about 70% indicates that the system is functioning, then when running you had a brief reading of 50% which is normal. As the system runs in realtime and has no memory faults will only show up as they occur.

The fault assigned to 90% is that of the EHA valve which is mounted on the side of the fuel distributor. It trims the fuel pressure which in turn increases or reduces the fuel quantity injected as required, a fault here could display the symptoms described.

The signal dropping to approx 80% indicates a problem with the air temperature sensor which sends a signal to the ecu in cold weather which richens the mixture. When this sensor fails it usually goes open circuit which tells the ecu its about minus 10 and in turn supplies more fuel to the engine than necessary.

The readings given may refer to faults in the the component or maybe the wiring and connectors.

As the EHA is controlled to some degree by the output of the air temperature sensor it may be that the faulty sensor is causing the eha to appear faulty.
The sensor being cheap and easy to test I would start with that.

It will be sited somewhere along the inlet tract before the air filter usually in the hose that draws air in from the front of the car. Unplug the connector and test the resistance using the ohms reading on the multimeter. Correct reading at around 15 to 20 degrees c is in the region of 2000 to 3500 ohms.
If you disconnect the sensor and po it in the freezer for a bit the rading should increase significantly.

Good luck

 

[ant500sl]

Just realised that you were road testing the vehicle, in my tables 80% is also shown when drive is engaged therefore it is likely that its the EHA valve.

This can be tested with a home made cable and a multimeter, replacement partcosts around £100 and is quite straightforward to install if required.

 

[38Kestrel]

just before I start taking things apart

Hi again,

Can I be clear on the following.

My pin 3 signal varies with throttle position when stationary or driving.
This is normal I guess.
The only "fixed" readings I've seen are 70%, 50% and 90%
the 90% occurs if left on idle for say one minute, the variable signal rises slowly to that point, it could therefore just be the variable signal but at 90% because of engine revs.

Am I being clear here? Somehow I doubt it.

Geoff

 

[ant500sl]

Codes do vary with year and have different meanings on vehicles with and without cats. If you let me have your chassis number I can call up the exact details for you car.

Will be away for a couple of days by the way.