I have some trouble understanding the pinout of my OBDII plug. It appears that it has both grounds, K-Line, 12V and CAN Bus low (according to standard obdII plug). Therefore it does not have even one complementary pair of signals. Yet, when I plug my Bluetooth OBDII scanner it communicates with ECU correctly. I have never noticed that before my ABS light came on. I was checking if in my 7th gen Civic there is a so-called Service Check System pin to force ABS light to communicate error codes in pulses. A bit puzzled by the pinout of my OBDII plug. Could someone explain the meaning of each pin? Thanks!
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1I'm pretty sure all it needs is either the K-LINE or CAN Low, battery power, and a ground to work.– Pᴀᴜʟsᴛᴇʀ2 ♦Sep 29, 2022 at 0:42
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Intresting. I was under impression that all communication in cars is a pair of differential signals like Flex and CAN. Hence my surprise when I looked at the OBDII port in my car.– WintermuteSep 29, 2022 at 19:48
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@Wintermute Even CAN isn't always differential. SAE J2411 defines single-wire CAN (SWCAN) which is most commonly found on GM vehicles as the physical layer for LS GMLAN. Other single-ended automotive links include the very common LIN bus and SENT.– user71659Jan 10 at 5:21
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2 Answers
https://pinoutguide.com/CarElectronics/honda_obd_2_pinout.shtml https://pinoutguide.com/CarElectronics/car_obd2_pinout.shtml
Generic readers decode P type errors as they're related to emissions. Your generic reader cannot decode manufacturer specific codes; B, C, and U codes requiring spending more to have a scantool similar to dealers. These scantools can provide (limited) programming coinciding with dealers access to online services of their manufacturer for updating programs when necessary. ABS generate C error codes with B and U codes for other issues. Autozone has upgraded their readers to decode abs errors so call ahead to check. Abs C codes would be something like C0045. If Autozone cannot decode your Honda abs code(s), then you might be able to force the abs indicator to flash codes by counting the number of flashes between pauses, repeating after displaying stored errors.
If I'm not mistaken, pins 2 and 5 are used for standardized (univeral P type) error codes. These are serial speed and slow. Canbus uses a different set of pinouts to connect modules in a parallel communication protocol for faster speeds. Generic readers only tap into pins 2 & 5. More expensive readers/scantools have capabilities of connecting to the other pinouts where abs codes are sent for decoding.
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Every OBD II port pinout shows pin 2 as J1850+ and pin 5 as signal ground for standardized serial communication of P type error codes.– F DryerSep 29, 2022 at 19:22
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@Pᴀᴜʟsᴛᴇʀ2 Yes, you are correct I have checked a few times as I was puzzled by it. This could explain why in my A3 from 2006 same device with the same app can read SRS and other more sophisticated codes. Sep 29, 2022 at 19:40
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@FDryer I heard of this puls method however I cannot find any information on how to force ECU to communicate using the dashboard cluster. One suggestion was to short pin 4 and 9 which obviously will not work in the case of Civic 7th gen. Sep 29, 2022 at 19:43
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@Wintermute I researched Honda info and there appears to be two methods to retrieve P type error codes; standard generic (USA) OBD II readers and certain Honda models and years describing jumpering pins in the OBD II port to force output of error codes using the instrument panel led display to flash. Counting number of flashes followed by a pause then flashing again gives a two number code. Repeated several times then moving on to another code. 1996 was the year when USA mandated all vehicles have OBD II regardless whether domestic or imported.– F DryerSep 29, 2022 at 19:55
I checked the pins with DMM and the voltages are as follows: Pin 4 0V, Pin 5 0V, Pin 7 12V, Pin 14 5V, and Pin 16 12V.
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If I'm not mistaken, the ELM327 is the universal chip for serial communications for most generic OBD II readers to decode generic/universal P codes. Dealer, repair shops and mobile techs have high end expensive scantools to decode manufacturer specific codes; B, C, U codes, have canbus access and programming capability. Serial comms are on two wires; one ground and one signal. Canbus uses two other wires for higher speed comms with a termination resistor. Virtually every generic reader does not have canbus capability since it means communicating using a different protocol from serial comms.– F DryerJan 11 at 20:24
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Interestingly in past, I worked with canbus from a signal integrity point of view and I remember that CAN like flex is a differential signal. This model of Civic does not use canbus it uses a single signal and GND in the "OBD2" port. Diagnostic tools such as Foxwell NT510, and NT630ect can pull the B, C and U error codes and communicate with SRS, ABS, and IMMO using this port. CAN is used in this car but not to communicate with the outside world. Jan 11 at 23:49
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I stand corrected as canbus in some automotive OBD II applications allow dealer direct communications using their proprietary scantool. The various online pinouts suggest this too.– F DryerJan 12 at 21:40
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typeaccord.co.uk/board/threa...7th-gen.23506 " On the 7th gen, HDS (or an ELM327) uses K-line. There is a K-line connection to the MICU (which acts as a proprietary gateway to CAN which HDS can read but some ELM327 cannot read). There is also a K-line connection to pin 23 on connector E of the engine ECU (not easy to find in the ESM) which is for direct reading of the engine ECU as provided for in the OBD2 standard (hence cheap generic readers can read the 7th gen engine ECU but nothing else)." Jan 13 at 0:45
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In other words, on the 7th gen pre-facelift (and probably the facelift) only the K-Line connection to the ECU is fully OBD2 compliant, the other K-Line connection to the MICU (which is the gateway to the other ECUs on the CAN) is proprietary. Thus if you buy something that does not explicitly say that it can read the ABS etc on a 7th gen Honda Accord, then you may be disappointed. The quote above is something I manged to find on the subject. Jan 13 at 0:45