Which OBD2 pins do you need to read the CAN bus?

Four are enough: CAN_H on pin 6, CAN_L on pin 14, signal ground on pin 5 as the transceiver reference, and battery positive on pin 16 to power the adapter. The chassis ground on pin 4 can serve as the power return. Fuse pin 16 inside the adapter and do not add a 120 Ω termination: the bus is already terminated at both of its ends.

Is pin 16 live with the ignition off?

Yes. SAE J1962 defines it as a permanent positive voltage, and interface vendors’ guides confirm it often stays powered with the ignition off. A device left plugged in therefore draws on the vehicle battery unless it goes to sleep. It is also why a short inside an unprotected adapter stays dangerous with the engine stopped: put a fuse in the adapter.

What is the difference between pins 4 and 5?

Pin 4 is chassis ground, bonded to the body, meant for the tool’s supply current. Pin 5 is signal ground, the reference for CAN, K-line or J1850 transceivers; a tool must not draw more than 1.5 A through it. J1962 asks the manufacturer to wire pin 5 to a clean point that limits noise and node-to-node offsets: it is the one to use as the transceiver reference.

How do I tell which OBD protocol my vehicle uses?

Look at which pins are populated in the port: 6 and 14 point to CAN, 7 alone or with 15 to ISO 9141-2 or KWP2000, 2 and 10 to J1850 PWM, 2 alone to J1850 VPW. It is only a hint, because the manufacturer may use those pins for something else. A tool such as the ELM327 tries the protocols one after another and gives the answer.

What is the difference between an OBD2 type A and type B port?

Type A, the car version, supplies 12 V nominal on pin 16; type B, meant for 24 V vehicles, supplies 24 V and carries a blue marking required by SAE J1962. A type B tool plug fits both, a type A plug does not fit a type B port. J1962 notes that US regulations do not allow more than 20 V at the port.

Can you use pins 1, 3, 8, 9, 11, 12 and 13?

Not without the manufacturer’s documentation. SAE J1962 leaves them to the manufacturer, who may put a proprietary bus, a switched supply or a workshop function there. The standard asks the tool to keep them high impedance, above 500 kΩ, until their use is verified. On a recent vehicle, several of them may carry Diagnostics over IP Ethernet.

What is the difference between the black and the green J1939 connector?

The black connector (type 1) dates from 250 kbit/s J1939 CAN. The green one (type 2), approved by SAE in 2011 and common on North American trucks from model year 2016, was added for the 500 kbit/s of SAE J1939-14. Pins A to E keep the same role; the green one has a smaller-diameter pin F.

Which pins carry the second CAN bus on a J1939 connector?

SAE J1939-13 leaves pins H and J to the manufacturer, and most recent trucks put a second CAN there (CAN_H on H, CAN_L on J). Some manufacturers use F and G instead, which otherwise carry J1708 / J1587, or put a third CAN on them. The main network always stays on C and D. Check the vehicle documentation before wiring F, G, H or J.

Pinout

OBD2 pinout: the J1962 16-pin OBD-II connector

The OBD2 (OBD-II) diagnostic port is the 16-pin connector defined by SAE J1962 and ISO 15031-3. Nine pins have a standard role: grounds on 4 and 5, permanent +12 V on 16, CAN on 6 and 14, K-line and L-line on 7 and 15, SAE J1850 on 2 and 10. The other seven are left to the manufacturer.

By Hugues Orgitello · Updated November 4, 2026 ·

J1962 type A connector, vehicle side (16 pins)

Allocation from SAE J1962 (table 1 and section 6.3), seen on the vehicle’s female connector. Pins 2, 6, 7, 10, 14 and 15 carry their standard signal only if the vehicle uses that protocol for OBD; otherwise the manufacturer may assign them elsewhere, as long as an SAE J1978 tool is not disturbed.

Pin	Signal	Standard	Description
1	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
2	J1850 Bus+	SAE J1850	SAE J1850 bus positive line: the only line in VPW, the + line of the pair in PWM (Signal)
3	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
4	Chassis GND	SAE J1962	Chassis ground, bonded to the vehicle chassis: power ground for the test equipment (Ground)
5	Signal GND	SAE J1962	Signal ground: reference for the tool’s transceivers (the tool draws 1.5 A at most) (Ground)
6	CAN_H	ISO 15765-4	CAN high line (Differential pair)
7	K-line	ISO 9141-2 / ISO 14230-4	K line, bidirectional: the tool sends and receives on it (Signal)
8	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
9	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
10	J1850 Bus-	SAE J1850	SAE J1850 bus negative line, PWM only (unused in VPW) (Signal)
11	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
12	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
13	Discretionary	Manufacturer	Manufacturer discretionary. May be wired (proprietary bus, supply, factory function): never assume it is free (Signal)
14	CAN_L	ISO 15765-4	CAN low line (Differential pair)
15	L-line	ISO 9141-2 / ISO 14230-4	L line, only on a two-wire ISO interface; not needed on many vehicles (Signal)
16	Battery +	SAE J1962	Permanent battery positive: 12 V nominal on type A, 24 V on type B (Power)

Pins used by each OBD protocol

A vehicle generally uses only one of these protocols for OBD. Pins 4, 5 and 16 serve all of them. A populated pin does not prove the protocol: the manufacturer may use it for something else.

Pin	Signal	Description
6, 14	ISO 15765-4 (CAN)	CAN_H / CAN_L pair, at 250 or 500 kbit/s. The protocol of recent vehicles (Differential pair)
7, 15	ISO 9141-2 / ISO 14230-4 (KWP2000)	K line on pin 7, L line on pin 15 only in the two-wire version (Signal)
2, 10	SAE J1850 PWM	41.6 kbit/s, differential pair Bus+ (2) and Bus- (10) (Signal)
2	SAE J1850 VPW	10.4 kbit/s, a single line on pin 2 (Signal)
4, 5, 16	GND, GND, Battery +	Shared by every protocol: chassis ground, signal ground, battery positive (Power)

J1939 9-pin Deutsch diagnostic connector (SAE J1939-13), type 1 black and type 2 green

Diagnostic port of heavy trucks, buses and off-highway machines, a 9-contact Deutsch HD10 connector (the letter I is not used). Type 1 (black) carries J1939 CAN at 250 kbit/s; type 2 (green) was added for the 500 kbit/s of SAE J1939-14. Pins F, G, H and J change from one manufacturer to another: check the vehicle documentation before wiring them.

Pin	Signal	Type 1 (black)	Type 2 (green)	Description
A	GND (battery -)	Ground	Ground	Battery ground (Ground)
B	Battery +	Battery +	Battery +	Battery positive, powers the diagnostic tool (Power)
C	CAN_H	250 kbit/s	500 kbit/s (or 250)	CAN high of the main J1939 network (CAN1) (Differential pair)
D	CAN_L	250 kbit/s	500 kbit/s (or 250)	CAN low of the main J1939 network (CAN1) (Differential pair)
E	CAN_SHLD	Shield	Shield	Shield of the CAN1 pair (Shield / earth)
F	J1708+ / CAN_H	J1708+	J1708+ or CAN_H	SAE J1708 / J1587 + line on type 1. On type 2, J1708+ or CAN high of an extra network, depending on the manufacturer (Signal)
G	J1708- / CAN_L	J1708-	J1708- or CAN_L	SAE J1708 / J1587 - line on type 1. On type 2, J1708- or CAN low of an extra network, depending on the manufacturer (Signal)
H	OEM (CAN2_H)	OEM	OEM	Left to the manufacturer. Most often the CAN high of a second network (CAN2) (Signal)
J	OEM (CAN2_L)	OEM	OEM	Left to the manufacturer. Most often the CAN low of a second network (CAN2) (Signal)

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When the OBD-II port became mandatory

In the United States, the EPA states that all 1996 and newer cars and light trucks carry OBD-II. In Europe, EOBD has been required on petrol cars since 2001; for diesel cars the sources we checked give 2003 or 2004, and only the directive text settles whether that is new type approvals or first registrations.

SAE J1962 places the type A connector in the passenger compartment, between the driver’s end of the instrument panel and 300 mm beyond the vehicle centerline, reachable from the driver’s seat without a tool or a cover to remove. The standard notes that US regulations are more restrictive on this location.

Pin 16: a permanent +12 V, to protect

SAE J1962 defines pin 16 as a permanent positive voltage: it powers the tool and is the reference for the K line, ignition off included. The standard recommends a fuse on the vehicle side, but an adapter must not rely on it: put a fuse or current limiter in the adapter itself, as close to the pin as possible.

The standard also recommends that every tool circuit survive any of its pins touching pin 16, up to 10 A, or grounds 4 and 5. The ELM327 reference circuit puts a diode in series with the pin 16 input ahead of the regulator. An adapter powered from elsewhere (USB, internal battery) must never feed voltage back onto pin 16.

Chassis ground (4) and signal ground (5)

Pin 4 is bonded to the chassis and is the tool’s power ground. Pin 5 is the transceivers’ reference; J1962 caps the current a tool draws through it at 1.5 A and recommends the manufacturer wire it to a clean point that limits noise and node-to-node offsets. Reference the CAN or K-line transceiver to pin 5, not pin 4.

On the tool, contacts 4 and 5 must make before all the others when plugging in and break last. ELM Electronics reports a few vehicles with no pin 5; on those, take ground from pin 4.

CAN bus on 6 and 14: termination and check

A CAN bus is terminated with a 120 Ω resistor at each of its two ends. Seen from the port, the two resistors are in parallel: with the vehicle powered off, expect about 60 Ω between pins 6 and 14. A value near 120 Ω points to a missing or badly connected termination, a value near 0 Ω to a short.

The reading only covers the segment wired to the port: if the port sits behind a gateway, it says nothing about the other buses. An OBD adapter joins the bus in the middle and must not add a third 120 Ω resistor, which would pull the total down to 40 Ω.

Manufacturer pins and common mistakes

Pins 1, 3, 8, 9, 11, 12 and 13 are left to the manufacturer, and SAE J1962 asks the tool to keep them high impedance (over 500 kΩ) until their use is verified. Diagnostics over IP (DoIP) also uses some of them for Ethernet; public sources disagree on the exact assignment, so we do not give it.

The most frequent mistakes: confusing chassis ground and signal ground; feeding supply back onto pin 16; assuming a populated pin carries the standard protocol, when pins 6 and 14 once served other systems before CAN; plugging a 12 V tool into a 24 V type B port.

J1939 network: backbone, stubs and termination

A J1939 network is a single, linear twisted pair, shielded in the SAE J1939-11 version, with each ECU joined to it by a short stub. The backbone is terminated with a 120 Ω resistor at each of its two ends: with the ignition off, expect about 60 Ω between pins C and D of the diagnostic port. A tool plugged into the port must not add a termination.

On the green port, North American on-highway makers generally put a second CAN on H and J, and sometimes a third on F and G in place of J1708; others use F and G for the second network. The Caterpillar 9-pin connector is not a J1939-13 port: battery positive on A, ground on B and CAN on F and G.

Frequently asked questions

FAQ

Which OBD2 pins do you need to read the CAN bus?: Four are enough: CAN_H on pin 6, CAN_L on pin 14, signal ground on pin 5 as the transceiver reference, and battery positive on pin 16 to power the adapter. The chassis ground on pin 4 can serve as the power return. Fuse pin 16 inside the adapter and do not add a 120 Ω termination: the bus is already terminated at both of its ends.
Is pin 16 live with the ignition off?: Yes. SAE J1962 defines it as a permanent positive voltage, and interface vendors’ guides confirm it often stays powered with the ignition off. A device left plugged in therefore draws on the vehicle battery unless it goes to sleep. It is also why a short inside an unprotected adapter stays dangerous with the engine stopped: put a fuse in the adapter.
What is the difference between pins 4 and 5?: Pin 4 is chassis ground, bonded to the body, meant for the tool’s supply current. Pin 5 is signal ground, the reference for CAN, K-line or J1850 transceivers; a tool must not draw more than 1.5 A through it. J1962 asks the manufacturer to wire pin 5 to a clean point that limits noise and node-to-node offsets: it is the one to use as the transceiver reference.
How do I tell which OBD protocol my vehicle uses?: Look at which pins are populated in the port: 6 and 14 point to CAN, 7 alone or with 15 to ISO 9141-2 or KWP2000, 2 and 10 to J1850 PWM, 2 alone to J1850 VPW. It is only a hint, because the manufacturer may use those pins for something else. A tool such as the ELM327 tries the protocols one after another and gives the answer.
What is the difference between an OBD2 type A and type B port?: Type A, the car version, supplies 12 V nominal on pin 16; type B, meant for 24 V vehicles, supplies 24 V and carries a blue marking required by SAE J1962. A type B tool plug fits both, a type A plug does not fit a type B port. J1962 notes that US regulations do not allow more than 20 V at the port.
Can you use pins 1, 3, 8, 9, 11, 12 and 13?: Not without the manufacturer’s documentation. SAE J1962 leaves them to the manufacturer, who may put a proprietary bus, a switched supply or a workshop function there. The standard asks the tool to keep them high impedance, above 500 kΩ, until their use is verified. On a recent vehicle, several of them may carry Diagnostics over IP Ethernet.
What is the difference between the black and the green J1939 connector?: The black connector (type 1) dates from 250 kbit/s J1939 CAN. The green one (type 2), approved by SAE in 2011 and common on North American trucks from model year 2016, was added for the 500 kbit/s of SAE J1939-14. Pins A to E keep the same role; the green one has a smaller-diameter pin F.
Which pins carry the second CAN bus on a J1939 connector?: SAE J1939-13 leaves pins H and J to the manufacturer, and most recent trucks put a second CAN there (CAN_H on H, CAN_L on J). Some manufacturers use F and G instead, which otherwise carry J1708 / J1587, or put a third CAN on them. The main network always stays on C and D. Check the vehicle documentation before wiring F, G, H or J.

Sources

SAE J1962, Diagnostic Connector (current edition) (paid or members-only document)
ISO 15031-3, Road vehicles, communication between vehicle and external equipment for emissions-related diagnostics, Part 3: diagnostic connector (paid or members-only document)
SAE J1962 (2002 edition), public copy incorporated by reference in 40 CFR 86.1806-05
ELM Electronics, ELM327 datasheet, Example Applications (J1962 vehicle connector, OBD interface circuit)
CSS Electronics, OBD2 explained: a simple intro
CSS Electronics, CAN bus explained: a simple intro (termination)
US EPA, OBD consumer brochure EPA420-F-02-016 (2021 archive snapshot)
Wikipedia, On-board diagnostics (secondary source, pinout and EOBD dates)
SAE J1939-13, Off-Board Diagnostic Connector (current edition) (paid or members-only document)
SAE J1939-11, Physical Layer, 250 kbit/s, Shielded Twisted Pair (paid or members-only document)
TE Connectivity (Deutsch), customer drawing HD10-9-1939P, HD10 receptacle arrangement 9-1939 (cavity layout)
Amphenol Sine Systems, AHD Series J1939 Type 1 & 2 on-vehicle data connectors (Type 1 and Type 2 pin table)
Opus IVS (DrewLinQ), Industry Connectors Reference rev 1.5 (SAE J1939 Type I and Type II, OEM variants)
CSS Electronics, J1939 explained: a simple intro
CSS Electronics, J1939 DB9 splitter adapter cable (second network on H/J or F/G)
Kvaser, J1939-13 Type II connection now available
Kvaser, J1939 introduction (physical layer)
Digi, Wireless Vehicle Bus Adapter connector pinout (9-pin Deutsch)

Tables built from these documents and cross-checked against manufacturer datasheets. Always check the datasheet of the connector you actually use: some manufacturers number differently.