6C-5 Power Assisted Steering System:
EPS Diagnosis General Description (LT-A750XP/ZK9)
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The P/S system in this vehicle is controlled by the EPS control unit. The EPS control unit has an self diagnostic system
which detects a malfunction in this system. When diagnosing troubles, be sure to have full understanding of the outline
of “Self Diagnostic System Description (LT-A750XP/ZK9) (Page 6C-5)” and each item in “Precautions in Diagnosing
Troubles (LT-A750XP/ZK9) (Page 6C-1)”, and then execute diagnosis according to “EPS System Check (LT-A750XP/
ZK9) (Page 6C-12)”.
Self Diagnostic System Description (LT-A750XP/ZK9)
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The EPS control unit performs the self diagnosis on the system and operates the “EPS” warning light (1) as follows.
• The “EPS” warning light lights when the ignition switch is turned to ON position (but the engine at stop) regardless
of the condition of the P/S control system. This is only to check if the “EPS” warning light is operated properly.
• If the areas monitored by the EPS control unit is free from any trouble after the engine start (while engine is
running), the “EPS” warning light turns OFF.
• When the EPS control unit detects a trouble which has occurred in the monitored areas the “EPS” warning light
comes ON while the engine is running to warn the driver of such occurrence of the trouble and at the same time it
stores the exact trouble area in memory inside of the EPS control unit.
Fail-safe Function Description (LT-A750XP/ZK9)
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If malfunction occurs in the EPS system, this sets fail-safe relay OFF. Consequently, the indicator light ON, and no
current will be applied to motor solenoid valve inactivating EPS and turning EPS indicator light ON. In this case, it
functions as the normal steering. If malfunctions occurs while EPS is being activated, the fail-safe relay will be set
OFF. Refer to “EPS Control Unit Diagram (LT-A750XP/ZK9) (Page 6C-7)”.
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