Why an IO12 works well for a 4L80E
The 4L80E needs four switched outputs for its solenoids, one analog input for fluid temperature and three digital inputs for the pressure switch manifold. An IO12 expander covers all of that and connects to your Haltech ECU over CAN, so it doesn't use up I/O on the main ECU. The flying lead harness gives you labeled bare wires to terminate however you like.
If you'd rather not build a loom, the Nexus Ti4L transmission interface kit is a ready-made alternative for Nexus owners.
What you'll need
- An IO12 expander and the IO12 flying lead harness, or the IO12 kit with flying lead harness.
- A 4L80E main connector pigtail. The build we based this on used ICT Billet's WPTRA38.
- Two pressure sensors and their connectors, for line/case pressure and converter/charge pressure.
- Deutsch DTM connectors for the spare circuits.
- Loom and finishing supplies, such as the harness sleeve pack, tape and glue-lined heat shrink.
- Crimp connectors or solder, crimpers, strippers, a heat gun and a sharp knife or scissors.
Step 1: Sort the IO12 harness
Pull these circuits out of the main bundle, since they won't go to the transmission:
- Power and grounds (signal ground, battery ground, 12 V battery and 12 V switched). Connect these as the IO12 instructions describe.
- DPI4, bundled with its signal ground and 12 V feed.
- AVI4, bundled with its signal ground and 5 V feed.
The 4L80E doesn't use DPI4 or AVI4, so keep them as spares for other jobs. We fit a DTM3 on DPI4 and either a DTM3 or a pressure sensor plug on AVI4. At the very least, insulate the 12 V and 5 V wires so they can't short.
Next, strip the labels from the four DPO bundles, AVI1 and DPI1 to DPI3. Leave AVI2 and AVI3 bundled with their own 5 V and signal ground. They'll get pressure sensor connectors rather than going into the 4L80E plug.
Step 2: Cut to length
Take the wires that will go into the 4L80E main connector and shorten them by 24" (about 600 mm), measured from their ends. That gives the AVI2 and AVI3 branches room to break out about 24" behind the transmission plug and reach their sensors.
Step 3: Connect the 4L80E main connector
The main connector carries the shift solenoids, the line pressure solenoid, the lockup solenoid, the fluid temp sensor and the pressure switch manifold. Eleven of its pins need connecting:
| IO12 circuit | IO12 wire color | 4L80E pin | GM wire color | What it runs |
|---|---|---|---|---|
| DPO1 | Purple/Black | A | Light green | Shift solenoid A |
| DPO2 | Purple/Brown | B | Yellow/black | Shift solenoid B |
| DPO3 | Purple/Red | D | Light blue/white | Line pressure solenoid, ground side |
| DPO4 | Purple/Orange | S | Brown | Converter lockup solenoid |
| 12 V | Grey/Red | C | Red/black | Line pressure solenoid, power side |
| 12 V | Grey/Red | E | Pink | Power to the other solenoids |
| AVI1 | Orange/Green | L | Yellow/black | Fluid temperature signal |
| Signal ground | Black/White | M | Grey | Fluid temperature ground |
| DPI1 | Grey, shielded | N | Pink | Pressure switch N |
| DPI2 | Grey/Black, shielded | P | Red/black | Pressure switch P |
| DPI3 | Grey/Brown, shielded | R | Dark blue | Pressure switch R |
DPI1 to DPI3 are shielded cables with a separate drain wire that is already grounded. Peel the shield back and connect only the inner signal conductor to the pigtail. Don't join the shield to the switch wire.
Step 4: Pressure sensors
Terminate AVI2 and AVI3, still bundled with their 5 V and ground, with pressure sensor connectors. One reads line or case pressure, the other converter or charge pressure. Split the two branches from each other where they leave the main loom so each can reach its sensor port. For configuring them in software, see our articles on the line pressure sensor and torque converter pressure sensor.
Step 5: Clean up and finish
You'll be left with spare signal ground, 5 V and 12 V wires. Cut them off, then seal each end with heat shrink or tape so nothing can touch ground. A cut power wire that rubs through to ground later is a frustrating fault to chase. Finally, sleeve and tape the harness so it's protected from heat and chafing near the transmission.
Before you power it up
- Check every connection with a meter against the table above.
- Confirm no spare 5 V or 12 V wire is exposed.
- Make sure the IO12's CAN ID matches what your ECU expects.
Then set up the solenoids, pressure control and shift tables in the software. Our transmission control and line pressure control articles cover the tuning side, and the Toyota A340E guide shows a complete base setup on another automatic.
FAQ
Can I use DPI4 and AVI4 for anything?
Yes. They're free after this build, so they're handy for extra switches or sensors.
Should I build it myself or buy the Ti4L?
If you're comfortable crimping and have the IO12 already, building is straightforward. If you want plug-in simplicity on a Nexus, the Ti4L saves the work. Talk to us if you're unsure which suits your car.
