Diagnostic plug uses explained?

[Jonathan]

Does a write-up exist explaining what the uses of the diagnostic plug are?

I ask because I want to put together the test lights to show which gear the auto trans is in. I have an old document I believe Welmoed put together showing how to do this using LEDs, but it doesn't explain much about the diagnostic plug itself. I would have thought it was in either the Workshop Manual or some tech bulletin, but I have looked and can't find one.

Is there something showing the pins labelled and what they are for? I only wanted something temporary and didn't see whether just any old 12 volt light bulb and receptacle would suffice tied into the right 12 volt pin and a ground pin for each of the two light bulbs to see what the auto trans is doing. That LED how-to write-up shows a resistor inline with the bulbs and a few other things I didn't quite follow.

[Ron]

See post 5 here: http://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor

[Bitsyncmaster]

The schematic only shows three wires on the diagnostic plug. One is +12 volts always on. One is ground. One is the dwell reading from the lambda ECU. I think there is also a pulse sender output which shows the RPM of the engine. There are no documented other function of the diagnostic plug.

[Ron]

See post 5 here: http://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor
OOPS! I should of said post 6.

[Jonathan]

Beauty Ron! Thanks a lot for the link. That gives me lots to read up on trying to understand the circuit.

I'm not convinced it is a governor problem, or anything really wrong with the transmission. I got poking around looking at things earlier today and I seem to have more slop in my throttle spool and linkage than what I would consider typical. I played around (engine off) with moving the spool and seeing when it starts to move the lever arm and it is not immediate in some circumstances. That may be the answer to why I was seeing some delay, or it might not. A couple times the other day it felt like I was taking off in third for a moment, like no oomph kind of thing, but then it goes like it would be expected to after pressing a bit firmer on the gas. I made a tightening adjustment to the linkage ends that other day so it could be just from not being familiar with the new pedal push point.

(it's nice to lean in and look around a cold engine though. Waaay easier than a hot one and once you've done it enough times, you've wiped off all the filth on previous shirt sleeves and the lookin' is good!)

Dave... after posting this and again looking through the workshop manual, I may have made it sound confusing as I wasn't after the rectangular diagnostic "socket" as much as the round diagnostic "plug" that's part of the shift computer harness. Was your description of connections for the one referred to in the manual as "socket" or the round plug one? The round plug one has 5 connections in more or less a circle pattern and the socket one for the rest of the car has 6 I think it is, including the one you use to check your dwell. No one in Dunmurry had yet heard the KISS advice back then, eh? (Keep It Simple Stupid!)

[Bitsyncmaster]

Yes I was referring to the engine diagnostic plug. I don't have an auto so did not even think about that plug.

[DMC-81]

Interesting thread. Referring to the square plug in the engine bay, I wonder if there was a diagnostic tool made for the dealers that plugged into it, or if it is compatible with a Volvo (etc) tool?

Dana

[David T]

Interesting thread. Referring to the square plug in the engine bay, I wonder if there was a diagnostic tool made for the dealers that plugged into it, or if it is compatible with a Volvo (etc) tool?

Dana

There are TWO diagnostic plugs, at least there are 2 on the automatics! Refer to G:04:01 fig 5 for the lights E1 and E2. In Ron's picture I think E1 is the upper one and E2 is the lower one. As for the engine diagnostic plug, refer to M:03:01-:02. There are SIX wires. There never was any service equipment sent to dealers to use the plug and the only point anyone every uses is Lambda wire to read duty cycle to check that the Lambda system is functioning and to adjust the mixture when necessary.