Is the harness between EFI ECU - ABS ECU normal?; Is the ABS actuator normal?; Check whether there is any poor contact at the connector section.

U0121 (blink 86) on Toyota Passo (KGC10): Abs Communication Failure

Short answer: U0121 means “Abs Communication Failure”. The car’s computer has found a fault in the Engine control (EFI) system and turns on the Check engine light (MIL). First check: is the harness between EFI ECU - ABS ECU normal?.

Code: U0121 · blink 86
System: Engine control (EFI)
Dashboard light: Check engine light (MIL)
Also sold as: Daihatsu Boon, Daihatsu Sirion (M300)
Applies to: 1KR-FE: M300 (Sirion export = JDM Boon M300S/M301S(4WD? see gaps) & Passo KGC10/KGC15). JDM-spec ECU not separately documented | K3-VE: M301 (Sirion 1.3 = JDM Boon M310S? / Passo QNC10)
Confidence: high (factory manual, export spec)
Source: carmanualsclub.com

Symptoms and when it is set

When communication signal cannot be received from ABS ECU

What to check, in order

Is the harness between EFI ECU - ABS ECU normal?
Is the ABS actuator normal?
Check whether there is any poor contact at the connector section.

Related on this car

← P1656/74 U0156/87 →

Clearing the code does not fix the fault. If it comes back, the problem is still there. For brakes, airbags and steering, see a trained mechanic.