What the Rebel K is
A K-swap usually means hacking up a donor harness or building one from scratch. The Rebel K takes that job off the table. It's a Nexus ECU made for Honda's K-series, paired with a terminated harness that already carries the factory-style plugs for the engine. The same box also runs the wideband O2 sensor, logs data on board and connects to your laptop or phone over Wi-Fi, so there's no separate wideband controller or logger to buy and wire.
It suits every factory port-injected K-series, which includes the K20A, K24A and K24Z families and their many sub-variants. Two hard limits: manual transmissions only (no automatics), and high impedance injectors only.
The Rebel JZ and Rebel LS are the same concept for Toyota JZ and GM LS engines. If you want background on the engine itself, our Honda K Series engine and why the K-series is special articles are a good read.
What's in the HT-220206 kit
The Rebel K kit (HT-220206) is built around the Rebel K ECU (HT-220003) and the main terminated harness (HT-186402). The sub-harnesses are what let that one main harness fit different throttle setups, injectors and gearboxes:
| Part | Why it's there |
|---|---|
| HT-220003 Rebel K ECU | Ships with 4 AWG ring terminals, nuts and washers, red and black boots, a Wi-Fi antenna, mounting bolts and a USB-C cable |
| HT-186402 main harness | Comes with the cabin adapter (HT-186130), alternator adapter (HT-186122), Honda pedal adapter (HT-186133), K20 and K24 crank sensor plugs, and a bag of plugs and pins for the spare I/O |
| HT-186016 Keihin injector harness | Plugs the factory-style Keihin injectors into the injector breakout |
| HT-186168 Honda DBW sub-harness | Runs the factory drive-by-wire throttle motor |
| HT-186169 Honda cable throttle sub-harness | Factory TPS and idle air control valve on a cable throttle body |
| HT-187011 and HT-187012 transmission sub-harnesses | 2002-04 and 2005-up manual gearboxes: speed sensor and reverse lockout solenoid |
| Sensor pack | Bosch LSU 4.9 (HT-010718) with weld-on bung, air temp sensor (HT-010206) with weld-on fitting, and a Bosch knock sensor with stud adapter and flanged M8 nut |
Running something other than Keihin injectors? Haltech makes three alternatives, sold separately: HT-186013 (USCAR EV6, GT150 style), HT-186014 (EV1, Timer style) and HT-186015 (Sumitomo, Denso style). Ask us if you need one.
What it won't talk to
Knowing this up front saves a lot of head scratching mid-install:
- The factory air temp, knock and O2 sensors aren't used. Their replacements come in the sensor pack.
- The VTEC pressure switch, thermofan switch and transmission reverse switch aren't read.
- The factory Honda ETC (electronic throttle control) module has to be bypassed or pulled out, so the Rebel K has full control of the throttle.
- There's no serial link to factory Honda DBW, BCM or ICC modules. That means no factory A/C request or factory coolant gauge once the Rebel K is in.
Do the map before the wiring
Like every Nexus ECU, the Rebel K wakes up on USB power alone, in a low power mode with all inputs and outputs turned off. Use it. Plug the laptop in on the bench, run the setup wizard, and get the injector, coil and output settings right before the ECU ever sees battery voltage. Powering up on the wrong settings is how coils and injectors get cooked.
The usual cautions apply: battery off while you wire, fuel lines and wiring kept away from heat, no bare wire left behind, and a check for fuel leaks before first start. Never charge or disconnect the battery with the engine running, because the ECU can see unregulated voltage. If you're welding anywhere on the car, unplug the harness from the ECU first.
Power, ignition and starter
The ECU has its own positive and negative battery studs, and both stay connected to the battery full time. Use red and black 4 AWG cable (not included), the supplied ring terminals and boots, and a 100 amp fuse on the positive side. Strip the cable so about 0.04 in (1 mm) of core pokes out of the terminal, and torque the stud nuts to just 2.2 ft-lb (3.0 Nm).
The pink wire wakes the ECU. It comes out of the cabin spare I/O connector (pin 5) as a loose lead. Feed it from the main ignition circuit, not accessory. Accessory power drops out while you crank, which would shut the ECU off mid-start.
Starter control is built in. The red/blue 10 AWG lead labeled STARTER is the ECU's 25 A auxiliary high current output (AX25+), and its plug fits the starter solenoid directly. For the ECU to know you want to crank, the white wire on AVI 1 (cabin pin 8) goes to the start terminal of the key switch. Running a CAN keypad? Put the start request on a button and AVI 1 is free for something else.
The alternator gets switched 12 V from a 2-pin DTM plug. The included HT-186122 adapter fits the common K-series alternator and has a 470 ohm resistor inline to excite it, standing in for the old charge light.
Crank, cam, VTC and VTEC
The crank sensor sits behind the crank pulley with its plug facing the exhaust side, near the oil filter. The harness ends in three loose terminated wires so you can fit whichever plug suits your engine. The pin order is different between the two, so double-check before you click it together:
| Pin | K20 plug (black) | K24 plug (gray) |
|---|---|---|
| 1 | Trigger + (yellow) | Switched 12V (red) |
| 2 | Sensor ground (black) | Trigger + (yellow) |
| 3 | Switched 12V (red) | Sensor ground (black) |
Both factory 3-pin cam sensors plug in. The exhaust cam sensor at the back of the head is the ECU's Home (sync) reference. The intake cam sensor at the front of the head is feedback for VTC, so the ECU knows where the intake cam actually is versus where it asked it to be.
The harness also plugs straight into the VTC solenoid by the timing chain cover and the VTEC solenoid. In NSP, VTC is set up with Cam Control and VTEC with Cam Control Switched.
Fuel, spark and engine sensors
| Connection | What to know |
|---|---|
| Injectors | Through a breakout plug, so the sub-harness only needs to match your injector connectors. Each plug is labeled by cylinder. High impedance injectors only. |
| Coils | Plugs straight into the factory K-series coils, no sub-harness needed. The coil ground is a 10 mm ring terminal that bolts to the head. |
| MAP | Plugs into the factory MAP sensor. For boost, use the 4-bar sensor inside the ECU, good to 43 psi, with a hose to the manifold or teed into the fuel regulator's reference line. The wizard asks which one you're using. |
| Coolant and air temp | The factory 2-pin coolant sensor plugs in. Air temp uses the supplied HT-010206 in its weld-on fitting. |
| Knock | One plug for the supplied Bosch sensor, which hears a wider frequency range than the factory one. See knock detection for setup. |
| Wideband | Direct plug for the LSU 4.9. It's what makes closed loop fuel and lean protection possible. |
| Oil and fuel pressure | Delphi 3-pin plugs for Haltech sensors such as the 150 psi or 250 psi TI sensor. It'll run without them, but we fit both for fuel pressure compensation and engine protection. |
| Flex fuel | Optional plug for the Haltech flex sensor (HT-011000). Our flex fuel tuning guide covers the tune side. |
That ring terminal only grounds the coils. The harness doesn't ground the engine, so the block still needs a proper strap back to the battery. A missing engine ground causes some of the strangest first-start problems we see.
Throttle, pedal, boost and gearbox
- Cable throttle: HT-186169 plugs into the factory 3-pin TPS and 3-pin idle air control valve.
- Drive-by-wire: HT-186168 plugs into the factory 6-pin DBW throttle body. Remember the factory ETC module has to go. Our drive-by-wire and DBW calibration articles cover the NSP side.
- Pedal: the HT-186133 adapter connects a Honda pedal to the 6-pin DTM on the cabin adapter. Using another pedal? The DTM pinout is pin 1 sensor ground, 2 APP 1, 3 and 4 5V, 5 APP 2, 6 sensor ground. Cabin pin 21 takes a brake switch or brake light signal that should read 12 V with the pedal pressed.
- Boost: a 2-pin DTM labeled BOOST is ready for a solenoid. We use Haltech's 3-port solenoid (HT-020400) for steadier control.
- Gearbox: the transmission breakout takes the 2002-04 or 2005-up sub-harness, which plugs into the factory speed sensor and, where fitted, the reverse lockout solenoid.
Fan, fuel pump, spare I/O and CAN
Two 10 AWG leads give direct 12 V to the thermofan (red/orange) and fuel pump (red/yellow). That lets the ECU prime the pump at key-on, kill it when it sees no RPM, and run the fan on temperature, with the A/C, or off above a set road speed if a speed sensor is fitted.
For extras, there's a 26-pin Superseal connector labeled CABIN and a 12-pin DTM labeled SPARE in the engine bay. Both mating plugs come in the kit. What's free to use:
| Connector | Spare I/O | Good for |
|---|---|---|
| Cabin (26-pin) | DPO 1, 2, 3 (pins 11, 13, 20) | Ground-switching outputs up to 3 A: warning lights, solenoids, or relay coils for bigger loads |
| Cabin (26-pin) | AVI 1 and 2 (pins 8, 10), SPI 1 (pin 22) | 0-5 V sensors and switches (AVI 1 is the start signal by default). SPI reads frequency or duty too. |
| Spare (12-pin, engine bay) | SPI 2 and SPI 5 (pins 11, 12), plus 5V, sensor ground, power ground and switched 12V | Wheel speed, an extra pressure or temp sensor. SPIs take hall or reluctor signals up to 25 V and 22.5 kHz. |
Cabin pin 17 also carries a tacho output. AVIs have a software-selectable 1K pull-up to 5 V, which you'd switch on for temp sensors and switches to ground and leave off for powered sensors.
There's a 4-pin DTM Haltech CAN connector at each end of the harness for a dash such as the uC-10, a keypad, a PDM or an IO16 expander. Add a CAN hub if you need more ports.
Rebel K at a glance
| Spec | Rebel K (HT-220003) |
|---|---|
| Ignition / injector outputs | 4 / 4 (high impedance only) |
| Heavy outputs | Fuel pump, fan and switched 12V (25 A each), plus AX25+ starter output |
| Throttle | 2 half bridge outputs for DBW or idle valve |
| MAP | Onboard 4 bar (to 43 psi), or the factory sensor |
| Wideband | 1 onboard controller, Bosch LSU 4.9 only |
| Comms | 2 CAN buses, USB-C, Wi-Fi with hardware lockout |
| Logging | 32 MB onboard, up to 1 kHz and 300 channels per log, 900 kB/s Wi-Fi download |
| Power supply | 8 to 22 V |
| Size and weight | 7.7 x 5.9 x 1.8 in (196 x 149 x 44.5 mm) with connectors, 2.53 lb (1.15 kg) |
On the software side you get the full Nexus toolbox: closed loop boost control, launch, flat shift, traction control, anti-lag, rotational idle, nitrous, flex fuel, knock control and long term fuel learning.
NSP, the setup wizard and Wi-Fi
Install NSP from Haltech, connect the USB-C cable and the ECU comes online in low power mode. The Rebel K wizard then asks, in order: a vehicle name (which makes a folder for its maps and logs), the base engine from the K-series list, which MAP sensor you're using, the cam profile, NA or boosted and cable or DBW throttle, your injectors, fuel regulator setup and base pressure, and your coils. You get a summary to check before it builds the base map. If your exact engine code isn't in the list, picking the matching main engine code is enough to get it running.
For Wi-Fi, enable the module under Connections, set an SSID (at least 1 character) and password (at least 8) under Wireless, click Apply, then turn the key on and join that network. Wi-Fi only works on main power, not USB. Two laptops can connect over Wi-Fi plus one over USB at once, and the free Haltech Connect phone app uses the same link for live data, gauges and clearing codes. More in our Wi-Fi article.
First start
- Battery charged, engine ground strap fitted, ECU bolted down.
- Key on: check every sensor reads sensibly in NSP, especially coolant, air temp, TPS or pedal, and MAP.
- Cycle the key to prime the pump, check fuel pressure and look for leaks.
- Crank briefly to make sure it turns over cleanly, then start it.
- Watch coolant temp and the wideband, and listen for anything unusual.
The power LED tells you a lot: green is normal, blue means it wants a firmware install from NSP, and red is a hardware fault. A yellow DTC light means there's a code stored, so check the DTC list.
The base map gets the engine running, it doesn't make it a finished tune. If you'd like us to tune it remotely, or check your parts list before you order, book a free 30-minute consultation.
Rebel K FAQ
Will the Rebel K run my K20 or K24 with an automatic?
No. Automatic transmissions aren't supported. The two included transmission sub-harnesses cover 2002-04 and 2005-up manual gearboxes.
Can I keep the factory coolant gauge and A/C working?
Not through the factory modules. The Rebel K doesn't talk to Honda's DBW, BCM or ICC modules, so there's no factory A/C request or coolant gauge signal. A Haltech dash or the spare I/O can stand in.
Do I need a separate MAP sensor for boost?
Not up to 43 psi. Plumb the ECU's built-in 4-bar sensor to the manifold and pick it in the wizard.
