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Codes from the ECU without the dataconnector thingy?


MVS Volvo Forums member -wj- has a 1996 Volvo 850 and needs to read the codes. “Can I get the ecu codes from the ecu without the normal dataconnector thingy? As in, can I connect a led/12v bulb to 2 pins on the ecu, and get the codes? edit: I’ts the motronic 4.3 one by the way.”

If you’re needing more information on how to read codes on your Volvo, see our Volvo Codes page.

MVS Contributor esl_97_850_T5 knocks it out of the park with his instructions on how to solve this.

The OBDII port pin 3 goes to Motronic 4.3 pin 5 for both USA/Canada ’97 850 and EU/Overseas ’97 850
(so probably does for ’96 also). See “On-board diagnostic system (OBD system)” diagram in:

1997 850 wiring diagrams

OBDII port pin 7 goes to Motronic 4.3 pin 36 for the ’96-’98 850 and S70/V70/C70/XC70 (for USA), which probably means for ’95-’97 850/S70/V70/C70/XC70 (for Europe and most anywhere else). OBDII port pin 7 is also what talks the keyword D3 B0 protocol (what I call KWPD3B0) to communicate with Motronic 4.4, COMBI, SRS, ABS, AW 50-42 (for gas auto transmission), Power Seats, ECC (for the first year S70/V70/C70/XC70, but not for 850 since 850 requires a flashing LED tool for ECC), and other ECUs which Vol-FCR shows for the 850/S70/C70/V70/XC70 in that time frame. See:

1997 850 wiring diagrams
rkam’s “1664-Diagnose-and-communication” thread

If you’re going to try using the flashing LED method, you might also check the several flashing LED examples mentioned in the following link, since at least one of them describes how to eliminate the separate 1800 ohm resistor which is displayed on your 2014-07-17 post‘s diagram:

volvo_850_diag_links.html flashing LED tool links

If you’re going to hook to the OBDII port, then your diagram from 2014-07-17 is valid, I think.

If you’re going to try using the flashing LED method, and if you’re going to hook directly to the Motronic 4.3 (instead of to an OBDII port), then I’d suggest first trying pin 5 (not pin 36), as indicated by the “On-board diagnostic system (OBD system)” wiring diagram in:

1997 850 wiring diagrams

To answer your question, I do think you can hook directly to the M43 pin 5. But I’ve never done it, so I’m no authority. I’m just inferring from what I’ve seen in the wiring diagram. Also, I have no idea if there’s any need for voltage transformations from the OBDII port pins to the pins on the M43 board. You’re on your own.

If pin 5 doesn’t work, then you might try using the flashing LED tool on M43 pin 36. But I advise against it. My experience (and the experience of some others) is that applying the flashing LED tool on the circuits connected through OBDII port 7 doesn’t work. Worse yet, there might have been generation of some new DTCs on various ECUs. Repeat: I advise against using flashing LED tool on Motronic 4.3 pin 36.

MVS and other sites have pages for the 3-digit Volvo DTC codes that probably apply to the Motronic 4.3 for your friend’s 850T5 (2.3 litre) engine. The page also includes a few of the associated P1234 codes:


If your Motronic 4.3 came from a USA car, you might be able to use an ELM327 and create yourself a
Data Link Connector to interface to the Motronic. If you do that, most any OBDII reader hardware and/or software would probably retrieve codes identifying fuel/ignition problems. The OBDII readers will usually report the DTCs in the P1234 format rather than the Volvo 1-2-3 format that the flashing LED tool reports them in (or the 2-digit raw hex format that volvo850diag uses).

Also, if you create a Data Link Connector, you can use Brick-Diag Free v0.0.6.6 to read the non-Motronic 4.3 codes. See the 5 Brick-Diag oriented items in the following list starting with:

some Brick-Diag intro with links

My experience is with:

– ELM327 devices (with volvo850diag, Realterm, Hyperterminal, STNterm),
– VAG/COM KKL cable (with Vol-FCR Demo, Brick-Diag Free v0.0.6.6, or Realterm), and
– a flashing LED tool to read/clear M43 DTCs (to see if the flashing LED approach would tell me anything in addition to the OBDII P1234 style DTCs),

and is congealed into the pages that feed from:

jonesrh’s “Volvo 850 OBDII (port) portal”

In addition to the links listed above and the Sweedspeed and Volvospeed sites that mecheng mentioned, I suggest you look at more of the links in:


On that page, take a look at:

– anything associated with mercuric (a member here on MVS) — he has lots of recent experience with disassembling M44, and he seems to also be very familiar with M43;
– the MotronicSuite stuff;

and consider exploring Motronic 4.3 / M43 stuff on:

MVS is like a gold mine when it comes to most anything relating to getting a newly bought Volvo working and keeping it working. There’s an immense wealth of info here! I can’t praise MVS, Matthew, and the contributors enough!!!

But, like you’ve observed, it’s true that MVS is not especially rich in detailed ECU knowledge. There’s some interest in tuning the engine/fuel ECU: Motronic 4.3, Motronic 4.4, etc. But few people care about the nitty, gritty details. For that it’s probably best for you to look primarily elsewhere. Hopefully this post will get you going in the right direction. I’ve given you plenty of “rabbit trails” if you follow the links on:


and if you explore the various other sites which you’ve been directed to (from this post) rather than just focusing strictly on the pages that I’ve sent you to.

850T5 (2.3 litre) running VERY rich, no data link connector

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