Wednesday 6 May 2015

OBD1READ :: What if your ECU is supported, but your wiring harness is missing wires?!

In the 90s TOYOTA decided to save money on wires...sometimes!

The diagnosis box will show spaces for signals and those signals won't have any wires and contact going to them. Looking inside the ECU can prove the ECU pinout is OK for OBD1READ to work. You would find TE2,VF,B+ and E1 at the ECU printed circuit board, but TE2 would be missing in the engine wiring harness that goes to the Diagnosis Box. Without TE2 it is not possible to trigger data output,so we need to get TE2 into the diagnosis box.

You can also be in this situation if you updated your ECU to a newer sibling , using an older wiring harness.
here is a few examples
ST165->92+ 3S-GTE
90-91 ST185->92+ 3S-GTE
90-91 EP82-> 92+ 4E-FTE

Here is what you can do to make your wiring harness OK to for use with OBD1READ.

 I suggest using micro screw drivers to work on releasing the contacts from a connector and diagnosis box, it takes some time to master this. I will not go into depth on this subject in this post.(You will probably need to do this to get your spare contacts from a junkyard harness)

You need to find TE2 inside the ECU,

Then you need to add a new contact wire to the corresponding ECU connector.

After you have a contact going into the connector you need to solder a wire to it and run that wire to the Diagnosis box.

At the diagnosis box you will need to install a contact for the missing TE2 pin and solder that contact with the wire you just installed. this is exactly like on the ECU connector except the contact is different from the ECU connector

After this you will be able to trigger the OBD1 data output like any supported cars.
You can use this proccedure to test that your wire addition worked

Cars that are known to be missing the TE2 wire but having supported ECUs

-1994 Toyota Corona 4A-FE Euro and JDM

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