ON-BOARD DIAGNOSTIC SYSTEM FUNCTION [ELECTRO HYDRAULIC POWER ASSIST STEERING (EHPAS)]SM1935226
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.
am3uun00000915

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.
am3uun00001162

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

System malfunction location

DTC (Mazda modular diagnostic system (M-MDS) display)

Fail-safe function

EHPAS warning light illumination status

Control status
Electric power steering oil pump
B1238
Illuminated
Control disabled
Battery power supply
B1317
Illuminated *1
Control disabled *3
B1318
Illuminated *2
Control disabled *3
Electric power steering oil pump (control module)
B1342
Illuminated
Control disabled
IG power supply
B1352
Illuminated
Control enabled
Module configuration
B2477
Illuminated
Control disabled
Electric power steering oil pump (motor)
C1099
Illuminated
Control disabled
CAN line
C1938
Illuminated
Control enabled *5
U0073
Illuminated
Control enabled *4 *5
U0100
Illuminated
Control enabled *4
U0140
Illuminated
Control enabled *5
U0155
Illuminated
Control enabled
U2023
Illuminated
Control enabled *6

*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: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.