Diagnostic ISO 7638 ABS/EBS

ISO7638 connection is the mandatory power supply for ABS/EBS systems. If the system is showing a wrong function, the power supply must be the first step of the diagnostic!

Before to use the table below, first check the reaction of the system at power ON, either with service brake applied (Brake pedal) or with the red coupling head disconnected (Emergency braking mode) or with the yellow line supplied (At 6.5 bar air pressure).

When switching power ON

Each modulator exhausts one time (the number of exhausts must be the same as the number of modulators).
ABS warning lamp on dashboard indicates a specific sequence (ON/OFF) or (ON/OFF/ON)

If not, check power supply :

Test points

(with 21W lamp)

Condition

Required value

Measured value

Comments

Power-A plug

1 - 4

ISO7638 connected

Switch power OFF

B+

If permanent power is missing (0V), solenoids are not powered.

If measured value is below B+ (voltage drop), it can indicate a resistance in the wiring.

Next steps :

check for oxidation marks in the connectors
check truck power supply
check the continuity of the wires with ohmmeter between ISO7638 socket/plug and ECU plug. (R<5Ω for correct operation)

Power-A plug

2 - 3

ISO7638 connected

Switch power OFF

0V

A permanent power indicates a wrong wiring or short circuit.

Next steps :

check for oxidation marks in the connectors
check truck power supply
check the wire position in ISO7638 socket/plug
check isolation between wires with ohmmeter

Power-A plug

2 - 3

ISO7638 connected

Switch power ON

B+

If switch power is missing, ECU is not powered.

If measured value is below B+ (voltage drop), it can indicate a resistance in the wiring.

Next steps :

check for oxidation mark in the connectors
check truck power supply
check the continuity of the wires with ohmmeter between ISO7638 socket/plug and ECU plug. (R<5Ω for correct operation)

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