snowblower
10-24-2026, 03:53 PM
My 2014 Yaris LE (France-built) developed permanently illuminated ABS and TRAC warning lights a while back. The problem first appeared immediately following a sudden stop in snowy conditions that activated the ABS system.
The two persistent diagnostic codes are:
C1428 – Motor Circuit Malfunction
C1203 – ECM Communication Circuit Malfunction
Both codes return after clearing.
C1428 diagnosis
According to the Toyota diagnostic procedure in ALLDATA, C1428 is reported when an open circuit is detected in the ABS pump motor circuit.
The procedure calls for checking the relevant fuses and the ground circuit at the brake actuator connector.
Results:
ABS NO.1 50 A fuse: Good
12 V supply at the fuse block: Good
GND2 resistance to battery negative: 0.27 Ω (Toyota specification is less than 1 Ω)
All checks passed. According to the Toyota diagnostic procedure, the next step is to replace the brake actuator assembly (Toyota part 44050-52D00).
C1203 diagnosis
Toyota describes C1203 as:
"Engine, drive source and destination variations that are sent from the ECM or main body ECU (multiplex network body ECU) do not match the ones of the skid control ECU (brake actuator assembly)."
The skid-control ECU is integrated into the brake actuator assembly.
I haven't completed the C1203 diagnostic procedure yet, but one of its possible conclusions is also to replace the brake actuator assembly.
My hypothesis: I'm thinking that the control board in the brake actuator assembly has failed. An internal electronic fault could potentially explain both C1428 and C1203.
All feedback is welcome. My goal is to complete as much diagnostic work as possible before drawing a final conclusion and ordering a used replacement assembly.
The two persistent diagnostic codes are:
C1428 – Motor Circuit Malfunction
C1203 – ECM Communication Circuit Malfunction
Both codes return after clearing.
C1428 diagnosis
According to the Toyota diagnostic procedure in ALLDATA, C1428 is reported when an open circuit is detected in the ABS pump motor circuit.
The procedure calls for checking the relevant fuses and the ground circuit at the brake actuator connector.
Results:
ABS NO.1 50 A fuse: Good
12 V supply at the fuse block: Good
GND2 resistance to battery negative: 0.27 Ω (Toyota specification is less than 1 Ω)
All checks passed. According to the Toyota diagnostic procedure, the next step is to replace the brake actuator assembly (Toyota part 44050-52D00).
C1203 diagnosis
Toyota describes C1203 as:
"Engine, drive source and destination variations that are sent from the ECM or main body ECU (multiplex network body ECU) do not match the ones of the skid control ECU (brake actuator assembly)."
The skid-control ECU is integrated into the brake actuator assembly.
I haven't completed the C1203 diagnostic procedure yet, but one of its possible conclusions is also to replace the brake actuator assembly.
My hypothesis: I'm thinking that the control board in the brake actuator assembly has failed. An internal electronic fault could potentially explain both C1428 and C1203.
All feedback is welcome. My goal is to complete as much diagnostic work as possible before drawing a final conclusion and ordering a used replacement assembly.