Fault code 1902: Diagnosis/troubleshooting

WARNING: Danger of injury from limbs being trapped or severed.

NOTE: To gain access to the driver's memory seat adjustment control unit, tilt the driver's seat back.

NOTE: Visual inspection: In the next troubleshooting section, first check that the affected pins on the driver's memory seat adjustment control unit plug connection are not damaged or corroded. The wiring and plugs of the affected components must also be checked for external damage and correct contact. Repair damaged or corroded pins if possible, otherwise replace affected pins. Repair or replace damaged wires.

NOTE: Sporadic faults: In the event of sporadic faults, wiring points attached to moving parts on and in the vehicle must be checked systematically. Various statuses that can cause faults must be simulated with the help of the wiring diagram.

NOTE: Battery voltage: A battery voltage of between 11.4 and 14.5 V is required for the following troubleshooting procedure. This must be checked and provided, if necessary. On the vehicle electrical system, the voltage to the fuse (input side) must be guaranteed.

NOTE: In the wiring harness from the driver's memory seat adjustment control unit to the horizontal lumbar adjustment motor, there is a disconnection point which must be included in the checks.

DIAGNOSIS/TROUBLESHOOTING PROCEDURE

Work instruction			Display OK	If not OK
1	Visual inspection	Switch off ignition Check plug connection at horizontal lumbar adjustment motor and on driver's memory seat adjustment control unit for damage (corroded or bent pins)	Go to Step 2	Repair plug → End
2	Check wires from driver's memory seat adjustment control unit to horizontal lumbar adjustment motor for short circuit to ground	Pull plug C off driver's memory seat adjustment control unit Pull plug off horizontal lumbar adjustment motor Measure resistance between pin 11 of control unit plug C and ground	∞ Ω Go to Step 3	The check relating to pin 1 is also to include pin 8 at the disconnection point The check relating to pin 2 is also to include pin 7 at the disconnection point Repair wire → End
2		Measure resistance between pin 2 of control unit plug C and ground	∞ Ω Go to Step 3
3	Check wires from driver's memory seat adjustment control unit to horizontal lumbar adjustment motor for short circuit	Measure resistance between pins 1 and 2 of control unit plug C	∞ Ω Go to Step 4	The check relating to pin 1 is also to include pin 8 at the disconnection point The check relating to pin 2 is also to include pin 7 at the disconnection point Repair wire → End
4	Check wires from driver's memory seat adjustment control unit to horizontal lumbar adjustment motor for open circuit	Measure resistance between pin 1 of control unit plug C and pin 1 of horizontal lumbar adjustment motor plug	< 5 Ω Go to Step 5	The check relating to pin 1 is also to include pin 8 at the disconnection point The check relating to pin 2 is also to include pin 7 at the disconnection point Repair wire → End
4		Measure resistance between pin 2 of control unit plug C and pin 2 of horizontal lumbar adjustment motor plug<	< 5 Ω Go to Step 5
5	Check wires from driver's memory seat adjustment control unit to horizontal lumbar adjustment motor for short circuit to B+	Switch on ignition Measure voltage between pin 1 of control unit plug C and ground	< 0.3 V Go to Step 6	The check relating to pin 1 is also to include pin 8 at the disconnection point The check relating to pin 2 is also to include pin 7 at the disconnection point Repair wire → End
5		Measure voltage between pin 2 of control unit plug C and ground	< 0.3 V Go to Step 6
6	Supply external power to horizontal lumbar adjustment motor	Using the 9684 measurement tool set, supply the motor with 12 V battery voltage	Motor starts Go to Step 10	Go to Step 7
7	Supply external power to horizontal lumbar adjustment motor	Remove motor for horizontal lumbar adjustment Using the 9684 measurement tool set, supply the motor with 12 V battery voltage	Motor starts Go to Step 8	Go to Step 9
8	Check mechanism of seat frame and repair or replace if necessary		→ End
9	Replace motor for horizontal lumbar adjustment		→ End
10	Replace driver's memory seat adjustment control unit		→ End