Friday, March 30, 2018

Wiring and power management

Direct wiring (swapped Honda ECU, etc.)

  • Use the following references to wire the scanner directly in case you swapped the stock ECU with an OBD1 ECU (all versions) or with an OBD2 A/B ECU (JDM, EU versions etc., excluding US versions!), in a car that doesn't have the 3 pin DLC connector available in the harness e.g. OBD0 '88-'91 (all markets), OBD2 '96-'01 (US market only).
    • Communication - connect to the communication pin designated as "TXD+RXD" or "K-Line" - i.e. DLC diagnostic data link:
      OBD1 ECU -> pin D7 (see OBD1 ECU pinout)
      OBD2 ECU -> (must not use US versions!) refer to a service manual (e.g. ECU P73 pin C8)
      (OBD2 US versions are incompatible, can be identified by letter "A" in the last 3 letters of the ECU id: 37820-P**-A**)
      hondash bluetooth interface obd1 ecu pinout
      pin-out diagram for A-B-D 3-plug OBD1 ECU version
    • Power - connect to any 12 V power source (alternative power feed option)
    • Ground - connect to any ground (chassis ground, etc.)

Wiring harness (OBD2A/B to OBD1 conversion, full engine and ECU swap, etc.)

  • make sure that the communication 5 V wire in DLC diagnostic connector is correctly connected to the ECU communication pin by tracing it manually using multimeter's continuity test
  • there are a couple of pins that output 5 volts, tracing the wire physically and making sure it's the correct one is mandatory, because it can read 5 volts even if it's connected to a wrong pin

OBD Bluetooth Scanner power management

  1. (Default) permanent power

    • the scanner stays permanently powered at all times when connected to the DLC port, even if the ignition is switched off, making the scanner drain an average current 4.9 mA. This is not an issue if you drive daily. However if you leave the vehicle sit for a longer period or your battery lifespan is ending, the scanner might contribute to quicker battery drain
      hondash bluetooth scanner permanent power
  2. Custom ignition switched power

    • with a little bit of electrician skill you can rewire your DLC connector to a ignition switched power source which will power the scanner only when the key is either in ACC or IGN position, in this example using a mini fuse tap at fuse Nr.27 in under-dash fuse box (cigarette socket power)
      hondash bluetooth scanner ignition switched power
    • if you're not willing to cut the wire, you can also simply disassemble the DLC connector and remove the middle female pin and isolate it, then proceed as described in 3rd option below.
  3. External power - OBD1 vehicles without power source in the DLC diagnostic connector

    • some OBD1 cars ('92-'95) don't have any power source in the DLC diagnostic connector (3 pin style connector with only two wires connected to it, middle pin and wire are missing). In this case you have to wire the scanner as described here

    • 1st step:
      prepare the wire on the scanner side
      * If you're using older V1/V2 scanner versions you can use the already pre-soldered wire, which is tucked in the case
    • 2nd step:
      connect the wire to an ignition switched +12V power source, for example using a mini fuse tap to tap the power at fuse Nr. 27 in under-dash fuse box (cigarette socket power), or splice the wire directly to the wire powering the cigarette socket, or use a cigarette socket plug to provide the power.
      hondash bluetooth scanner external power 2
    WARNING: Make sure there is no power in the DLC connector, when doing this mod, using two power supplies (DLC connector power source + external wire to another power source) simultaneously may permanently damage the scanner and blow fuses.