Hi Asman Farah, thank you for your question.

From experience with Myvi 2007 (DVVT / non-DVVT) models, when an OBD2 scanner is unable to communicate with the ECU even after ECU replacement, the issue is commonly not caused by the ECU itself.

Below are the most common causes observed:

1. OBD Port Power / Ground Issue

- Pin 16 (battery power) or pin 4/5 (ground) at the OBD port may not be supplying proper voltage or grounding.

- Even if all fuses are intact, there may be:

a) Loose or backed-out OBD connector pins

b) Corrosion at the OBD socket

c) Broken or partially damaged wiring between the fuse box and the OBD connector

Without proper power or ground, the scanner will not be able to establish communication with the ECU.

2. ECU Main Relay (EFI Relay) Fault

- A faulty or stuck ECU / EFI main relay can prevent the ECU from powering up fully, resulting in “ECU not detected” during scanning.

- Relays may fail internally even if they click or appear normal during basic checks.

- This is a common failure point on older Myvi models.

3. CAN / K-Line Communication Issue

- Some early Myvi models use K-line (ISO 9141) communication instead of CAN bus.

- If the K-line wire is shorted to ground or to battery voltage, the OBD scanner will not communicate at all.

- Wiring damage, poor splices, or past repairs can cause this issue.

4. Aftermarket Accessories Interference

- Aftermarket alarm systems, immobilisers, GPS trackers, or audio installations that tap into ECU or OBD wiring may disrupt communication signals.

- Poorly installed accessories are a frequent cause of intermittent or total OBD communication failure.

5. Recommended Next Steps

- To properly confirm the root cause, the following checks are recommended:

a) Measure 12V supply at OBD pin 16 using a multimeter

b) Verify ground continuity at OBD pin 4 and pin 5

c) Test or swap the EFI / ECU relay with a known good unit

d) Inspect K-line or CAN wire continuity from the OBD port to the ECU

e) Test with a professional diagnostic scan tool (e.g. Launch, Autel) to rule out scanner compatibility issues

As these tests require proper diagnostic tools and electrical testing, it is advisable to have the vehicle inspected at a qualified workshop or authorised service centre to accurately identify the fault and avoid unnecessary part replacement.

Hope this helps clarify the possible causes and next steps