Kalmar - MSARB Seat Sensor (LCD) Diagnostic

Modified on Fri, 13 Feb at 3:07 PM

1. Fault Overview

A yellow and black circle with black text

AI-generated content may be incorrect. When the LCD screen ‘Fault Detected’ menu option displays a Seat Fault, and the MSB Fault Light remains constantly illuminated when the ignition is turned to ON (right),

Access MSB and Screen Faults sub-menu by pressing and holding red fault symbol on screen or via holding the menu button for 3 seconds.

Open circuit seat sensor circuit

Short circuit seat sensor circuit

No driver detected on seat vehicle moving

Seat input always active

The fault conditions will be one of below:

Conditions for setting fault

Faulty seat sensor.
Open/short circuit in seat sensor harness.
Internal MSB ECU fault.

NOTE 1: The display will show an “Active” seat fault under the main screen icon of the LCD (top right-hand corner), and at the same time store the fault.

The seat fault will not be displayed once the fault becomes “Inactive” under the main screen icon of the LCD.

The red fault symbol will remain until 3x cycles of the Ignition supply.

NOTE 2: A seat fault will occur after FIVE (5) occurrences of the vehicle park brake being applied with no recognition of the operator being off the seat.

NOTE 3: The MAX-SAFE Anti-Rollaway Brake System™ will continue to function when the fault in Note 2 is active. The Seat Sensor is considered to be unoccupied at all times when this fault is active. If this fault is active the Road Speed trigger point is lowered from 6mph to 3mph.

NOTE: The MAX-SAFE Anti-Rollaway Brake System™ will continue to function when this fault is active. The Seat sensor is considered to be unoccupied at all times, when this fault is active.

After completing diagnosis and rectifying any faults, a full system test must then be performed and documented on the Systems Confirmation Test – MAX-SAFE Anti-Rollaway Brake System test sheet prior to returning the vehicle to service.

2. Diagnostic Procedure

Prior to undertaking the following diagnostic procedure, ensure that all electrical connections are securely attached, adjusting as required.

STEP 1: Locate 2-pin connector marked “S-seat” and disconnect.

Measure resistance of the seat sensor across Pins 1 & 2 of connector. Refer to Table 1.

Within specification: Continue to STEP 2.

Not within specification: Replace seat sensor. Verify repair with Full System Test.

Table 1: Expected resistances. All values (+-5%).

Step	Resistance of Seat Sensor
Resistance of Seat Sensor (seat unoccupied).	100 kΩ
Resistance of Seat Sensor (seat occupied).	Less than 5Ω

STEP 2: Keep the 2-pin seat sensor (S-Seat) connector disconnected.

Using a multi-meter, perform a voltage test on the wiring harness, while the vehicle power is on.

Test the voltage of the red wire (pin 1) of the 2-pin seat sensor connector with reference to GND (B-). Refer to Table 2.

Test the voltage of the yellow/red wire of the 2-pin seat sensor connector with reference to GND (B-). Refer to Table 2.

Test the voltage of the red wire of the 2-pin seat sensor connector wiring when connected to the yellow/red wire of the 2-pin seat sensor connector wiring. Refer to Table 2.

Within specifications: Continue to STEP 3.

Not within specifications: Replace wiring harness. Verify repair with Full System Test.

Table 2: Voltage of 2-pin seat sensor connector plug wiring (Reference voltage).

Test	12-volt system
Voltage on red wire when connected to GND (B-).	12V - 14V
Voltage on yellow/red to GND (B-).	0V
Voltage on red wire when connected to yellow/red wire.	12V - 14V

STEP 3 Disconnect the grey connector (12-pin) at the ECU. Locate the yellow/red wire (Pin 12). Perform a continuity test of the yellow/red wire located at the 2-way seat sensor (S-Seat) connector (Pin 2). Refer to Table 2.1.

Test the resistance of the yellow/red (Pin 12) wire from the ECU grey connector when connected to a GND (B-). Refer to Table 2.1.

Disconnect the black connector (12-pin) at the ECU. Locate the red wire (Pin 7). Measure resistance between red wire (Pin 7) of ECU and the red wire (Pin 1) of the seat sensor connector (S-Seat).

Within specifications: The ECU has failed. This scenario is unlikely: repeat all testing again to ensure that it is the ECU that has failed. If all testing has been repeated and testing still indicates that the ECU has failed, replace the ECU.

Verify repair with Full System Test.

Not within specifications: The wiring harness has failed; replace the wiring harness, verify repair with Full System Test.

Table 2.1

Test	Resistance
Resistance yellow/red (12-pin) to yellow/red (2-pin).	Less than 5Ω
Resistance yellow/red (12-pin) with reference to GND (B-).	5.4 kΩ to 5.8 kΩ
Resistance red (12-pin)/red (2-pin).	1.5 kΩ

3. Full System Test

Undertake a full system test of the MAX-SAFE Brake System and document the results on the test sheet found within the document Systems Confirmation Test – MAX-SAFE Anti-Rollaway Brake System prior to returning the vehicle to service.

Should the testing outlined within the Systems Confirmation Test fail for any reason, the system must be thoroughly inspected, diagnosed, and repaired as per the relevant Diagnostic Process Flow and Procedure document, prior to the vehicle being returned to service.