Reading obd1 codes
 

Not sure if it's true or not but I have heard that there's a way to read obd1 codes on a 93 940 turbo without having the read tool.

thats correct, the reader is built into the car, its a little back box under the hood, remove the top, there's a button and LED and 8 numbered sockets, you plug the jumper into #2 for ECU (fuel injection) codes, and #6 for ICU (ignition codes).

see Engine and OBD Diagnostic Codes

'DTM #1' reads the codes. DTM #2 reads some sensors but is less useful except in special sitatuions, and DTM #3 pulses a bunch of the actuators so you can test subsystem functionality. each of these has different functions with the jumper in pin 2 or 6. there's possibly also other jumper positions for cruise control, ABS, and maybe even ECC (which a 940 probably doesn't have) and power seats (a 940 *might* have)

OBDI doesn't even have a way other than flashing lights to give codes--no machine to hook up... Unfortunately the information one gets from OBDI is "hit and miss"--i wouldn't go throwing parts away and changing things solely based on codes. Especially when there are multiple codes... It is a starting point.

indeed. I would clear the codes and wait for them to reappear, then treat them as clues or hints, not direct diagnosis.

Hey guys. Have read volvoclub.org.uk on how to clear codes using the OBD1, apparently I can’t understand the Queen’s English, can’t seem to make happen what the text says I should be able to, if you guys have been able to do it successfully can I get a re-phrase/walk-through?…

read all codes in a position (#2 for fuel system)
(read codes until they start to repeat)
hold button down 8 seconds
release (light comes back on)
hold button down 8 more seconds, all codes should be gone, check by
hold button down 2 second, wait 2 seconds
should flash back 111 if all codes are erased

Often the official way doesn't work, I just disconnect the battery for a few minutes.

Hey there hoonk, lev:

Indeed, disconnecting battery with the stand-by 10mm wrench in the glovebox is super-straightforward and consistently effective. Only because I'm lazy and impatient did I want to see if I could shave off a few seconds and conserve a few joules or calories or whatever when it's time to clear codes. (Been doing it a lot lately; pretty sure I've got a bum wire somewhere in the connector to the knock sensor.)

Thanks to hoonk for providing this synopsis of the Brit method; providing interlinear reaction/commentary/amplification here FWIW:
So my first dumb question was: Press button in the middle of a code flashing? Or wait till it's done? Still don't know if it matters, but settled on waiting for flash sequence(s) to end before...
Next dumb question was: Press button [again] before the light that came back on goes dark (as it will do)? I did conclude by the end that one has to jump on this, smash that button before that holding-steady light winks out (the wording of the Brit description does make it sound like one should be watching for the light to go out as one is holding the button down)...

The Brits make explicit that the button should then be released [again], which release causes light to go dark, at which point...
Here was my weirdest/most important find, I think. At first I found that, after [again] releasing button, I couldn't the light to flash any info, not by holding for 2 seconds, 8 seconds, longer; nothing made it go. Until I tried turning car off then ON again. Then I would get my 111.

Waited till I could successfully repeat this "hack" three times before posting here.

Again, FWIW.

UPDATE: Seems this car off/car on hack doesn't always work the first time.... sometimes I get a flashing red light after doing the 2-second hold-down.... but then it will work the next time. (???)