ON-BOARD DIAGNOSTIC SYSTEM FUNCTION [ELECTRO HYDRAULIC POWER ASSIST STEERING (EHPAS)]
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Malfunction Detection Function
• The malfunction detection function detects malfunctions in the input/output signal system of the EHPAS control module (built into the electric power steering oil pump) when the ignition is at ON or driving the vehicle.
• The EHPAS warning light illuminates according to the following figure when the ignition is switched to ON to inspect for open circuits in the light.
Malfunction Display Function
• When the malfunction detection function detects a malfunction, the EHPAS warning light illuminates to advise the driver. Using the external tester communication function, DTCs can be output to the DLC-2 via the CAN line. At the same time, malfunction detection results are sent to the memory and fail-safe functions.
Memory Function
• The memory function stores DTCs of malfunctions in input/output signal systems. With this function, once a DTC is stored it is not cleared after the ignition has been switched off, even if the malfunctioning signal system has returned to normal.
• Since the EHPAS CM has a built-in non-volatile memory, DTCs are not cleared even if the battery is removed. Therefore, it is necessary to clear the memory after performing repairs. Refer to the Workshop Manual for the DTC clearing procedure.
DTC 5-digit code definition
• When related systems or components have failed, the CM stores the DTC of the malfunctioning part in the CM memory, and allows for the retrieval of the store data using scanning tool when necessary. The DTCs are indicated using five digits. Each digit indicates the following.
Fail-safe Function
• When the malfunction detection function determines a malfunction, the EHPAS warning light illuminates to advise the driver. At this time, the fail-safe function disables system control or gradually reduces the assist power.
DTC Table
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System malfunction location
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DTC (Mazda modular diagnostic system (M-MDS) display)
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Fail-safe function
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EHPAS warning light illumination status
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Control status
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Electric power steering oil pump
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B1238
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Illuminated
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Control disabled
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Battery power supply
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B1317
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Illuminated*1
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Control disabled*3
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B1318
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Illuminated*2
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Control disabled*3
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Electric power steering oil pump (control module)
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B1342
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Illuminated
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Control disabled
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IG power supply
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B1352
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Illuminated
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Control enabled
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Module configuration
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B2477
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Illuminated
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Control disabled
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Electric power steering oil pump (motor)
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C1099
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Illuminated
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Control disabled
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CAN line
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C1938
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Illuminated
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Control enabled*5
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U0073
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Illuminated
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Control enabled*4*5
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U0100
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Illuminated
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Control enabled*4
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U0140
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Illuminated
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Control enabled*5
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U0155
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Illuminated
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Control enabled
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U0401*6
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Not illuminated
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Control enabled*7
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U2023
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Illuminated
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Control enabled*8
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*1 :Illuminates when battery voltage is more than 17.5 V.
*2 :Illuminates when battery voltage is less than 9 V.
*3 :Controlled motor speed is decreased to 391 rpm per s until it is set at 0 rpm, and control is disabled.
*4 :Motor is stopped: Maintained at condition when stopped. Motor is rotating: Controlled vehicle speed is increased to 20 km/h {12 mph} per s until it is set at 200 km/h {124 mph}, engine speed is set at 1,000 rpm, and control continues.
*5 :Controlled steering speed is decreased to 100 degree per s until it is set at 0 degree, and control continues.
*6 :Only vehicles with i-stop.
*7 :EHPAS i-stop control is not operated, and normal control is maintained.
*8 :Motor is stopped: Engine speed and vehicle speed assimilation stops. After the motor is restarted, vehicle speed is set at 200 km/h {124 mph} and engine speed is set at 1,000 rpm, and control continues. Motor is rotating: Controlled vehicle speed is increased to 20 km/h {12 mph} per s until it is set at 200 km/h {124 mph}, engine speed is set at 1,000 rpm, and control continues.
