OBD2 port (DLC) add-ons for scan-tool owners: memory-saver cables for battery swaps, extension and Y-splitter cables, and port locks/covers

OBD2 memory saver cable · October 27, 2026

Every accessory that plugs into the 16-pin diagnostic link connector (DLC, standardised as SAE J1962) does one of three jobs. Choose the job first, because the products are not interchangeable.

Battery swap: a memory-saver cable feeds 12V into the port’s always-live pin while the main battery is disconnected. It is meant to keep radio presets, clock and learned values alive.
Reach and sharing: an OBD2 extension cable moves a Bluetooth dongle or handheld scan tool to somewhere you can reach. A Y-splitter cable gives you two female ends so a dongle and a second device can share the port.
Theft protection: a port lock or cover physically blocks plug-in access to the DLC.

Most people need only one of these. The three jobs pull in different directions: a lock stops anything from plugging in, a splitter invites more devices, and a memory saver puts your own power source on a circuit the car normally powers itself.

Memory-saver cables: what they hold alive and where they fall short

A memory saver connects a small power source to the DLC. The power source is usually a 9V battery pack or a 12V jump-starter pack, and it connects through a cable ending in a J1962 male plug. Power goes in on pin 16 (unswitched battery positive) and returns on pin 4 (chassis ground) or pin 5 (signal ground). That keeps a trickle of voltage on the vehicle’s keep-alive memory (KAM) circuits.

What it can help preserve: radio presets and security codes, clock, trip data, and on some cars the learned idle and throttle-body values the ECU would otherwise need to relearn after a battery disconnect. What it cannot promise: that every module stays awake. Some body control modules (BCM) and power-window modules lose their one-touch calibration anyway, and some cars still want a throttle or idle relearn drive cycle afterwards.

The main failure mode is a weak source. If the pack sags below what the car’s always-on loads draw, the saver does nothing. A second failure mode is current: a door left open, a dome light, or a key in the ignition can load the circuit well beyond what a 9V pack supplies. Treat the saver as insurance for a short swap, not as a substitute for a battery that can be changed quickly with the doors closed and the key out.

Memory-saver compatibility checklist before you plug in

Check these before buying or using one.

Is pin 16 always live? On most cars it is. On some vehicles the DLC power is switched or relay-controlled, so a memory saver does nothing. Look in the owner or service manual’s fuse diagram for the DLC circuit.
Fuse rating on the DLC circuit. The port is usually on a fused circuit shared with other loads, and ratings vary by vehicle. A saver that backfeeds a heavy load can blow that fuse, which then also kills your scan tool’s power.
Polarity protection. A cable with reverse-polarity protection or an inline fuse is a better design than a bare pair of leads. Reversed polarity into modules can do real damage.
Source voltage. 12V systems only. Do not feed 12V into a 24V truck circuit, and do not assume a 12V saver is right for heavy-duty vehicles.
Start-stop and AGM cars. Many need a battery registration or battery management system (BMS) reset after replacement. A memory saver does not replace that step, which usually needs a scan tool with service resets.
Hybrids and EVs. The 12V auxiliary battery procedure is vehicle-specific and sometimes tied to the high-voltage system. Follow the manufacturer’s service procedure rather than a generic saver, and treat the traction battery as a separate topic.

Extension cables: reach, shielding and pin pass-through

An OBD2 extension cable is a male J1962 plug on one end and a female socket on the other, with a cable between. The reason to buy one is practical: the DLC sits high under the dash on some cars and deep in a kick panel on others, and a Bluetooth dongle or handheld scan tool hanging from it is awkward to read or easy to knock loose.

What actually decides the purchase:

Full 16-pin pass-through. Some cheap cables wire only the pins needed for CAN (pins 6 and 14, CAN High and CAN Low) plus power and ground. That works on most newer cars. It fails on older vehicles using ISO 9141 K-line (pin 7) or J1850 (pins 2 and 10). If you diagnose older cars, check that every pin is carried through.
Cable length and shielding. CAN is a twisted-pair bus. A long, unshielded, loosely built cable can add noise and cause dropped frames, odd readings, or refused connections. A moderate length with good conductor gauge is safer than the longest cable available.
Wire gauge for power. Thin power conductors add voltage drop, which matters when a tool is doing a flash or a long test that needs steady supply.
Connector fit. A loose-fitting socket interrupts communication mid-session, which is worse than a failed read on a bidirectional or coding job.

For programming, module flashing or anything where a dropped connection can leave a module in a bad state, plug directly into the DLC instead of adding a cable.

A Y-splitter (splitter cable) has one male plug and two female sockets. The typical buyer wants a Bluetooth dongle left plugged in for a phone app while keeping the port free for a handheld scan tool, or wants a dash-camera or gauge power lead alongside the dongle.

The wiring is simple, but the electrical situation is not. Both devices sit on the same CAN bus and the same pin 16 supply. Two devices that both transmit requests can collide with each other or confuse the responding ECU. A phone app polling live data in the background while a handheld runs a bidirectional active test is the standard problem: you get timeouts, garbled readings, or an aborted service reset. A passive logger or a power-only accessory is far less risky than two active scanners.

Other things to check:

Pass-through of all pins. As with extension cables, some splitters connect only some of the pins.
Parasitic draw. A dongle left plugged into pin 16 draws power while the car sits. Some adapters sleep, some do not. On a car that sits for weeks, a splitter that keeps two devices powered makes a flat battery more likely.
Physical strain. Two sockets and a dongle hanging below the dash can interfere with knee clearance and the driver’s footwell.

If you want a simple rule: use a splitter for one active diagnostic device plus one passive or power-only device, and unplug the dongle before any serious bidirectional work.

Port locks and covers: what they stop and what they don’t

A port lock is a steel or hardened housing that closes over the J1962 socket, secured with a key or a bolt. A port cover is a plastic dust cap, which keeps debris out but is no deterrent. The lock’s purpose is to block a thief who plugs in a tool to program a blank key through the DLC, or who uses the port to reach the vehicle’s CAN network.

Know its limits. A lock only protects the DLC. Reported CAN-injection attacks on some vehicles reach the bus through other connection points, such as wiring behind lamp assemblies, so a port lock will not stop those. It also does nothing against relay attacks on keyless push-start systems, where the thief amplifies the key fob signal and never touches the port. Treat it as one layer alongside a pouch or box for the fob, a steering lock, and ordinary parking habits.

Practical points before buying:

Fit to the port shape and recess. Dash trim and port position differ across vehicles, so check that the lock clears the surrounding panel.
Material and fastening. A thin plastic cover that pries off is cosmetic. A steel body with a keyed latch is the real thing.
Access for inspection. Emissions inspection stations and your own scan tool need the port. A lock is something you remove, so keep the key somewhere you will find it.
Not compatible with a left-in dongle. A lock needs the port empty.

What none of these accessories will do

Short list, so expectations are right:

A memory saver does not charge or test a battery, and it is not a battery tester. Load, cranking and alternator checks are separate tools.
An extension cable or splitter does not add capability to a scan tool or dongle. A dongle that cannot read ABS or SRS modules still cannot after you add a cable.
A splitter does not make two active scan tools safe to run together.
A port lock does not stop relay theft or attacks through other CAN access points.
None of them fix an ELM327 clone that drops connection or a dongle with a weak Bluetooth link.

If your problem is that a tool cannot connect, start with the adapter and the vehicle’s protocol rather than adding hardware to the port.

Shop OBD2 memory saver cable for OBD2 port (DLC) add-ons for scan-tool owners: memory-saver cables for battery swaps, extension and Y-splitter cables, and port locks/covers

Get Obd2 Memory Saver Cable

Shop OBD2 extension cable for OBD2 port (DLC) add-ons for scan-tool owners: memory-saver cables for battery swaps, extension and Y-splitter cables, and port locks/covers

Get Obd2 Extension Cable

Shop OBD2 port lock for OBD2 port (DLC) add-ons for scan-tool owners: memory-saver cables for battery swaps, extension and Y-splitter cables, and port locks/covers

Get Obd2 Port Lock

FAQ

Can I use an OBD2 memory saver on any car?

Only if pin 16 on your car’s DLC is always live. Some vehicles switch or relay that circuit, and the saver then does nothing. Check the fuse diagram, and use a 12V saver only on 12V systems.

Is it safe to leave an OBD2 dongle plugged in through a splitter?

It depends on the dongle. Some adapters sleep when the ignition is off, and others keep drawing from pin 16 and can flatten a battery on a car that sits for weeks. Unplug it before long storage and before bidirectional tests with another tool.

Will an OBD2 port lock stop CAN injection theft?

It stops someone from plugging into the DLC, but not attacks that reach the CAN bus through other wiring, such as behind the headlight. It also doesn’t stop relay attacks on keyless push-start. Use it as one layer.