Pinpoint Test M : DTCS P1812:00, P1815:00: Notes

WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.

Refer to TWO WHEEL DRIVE/FOUR WHEEL DRIVE SYSTEMS for schematic and connector information.

Normal Operation

The MSS contains a set of resistors that communicate the operator's choice to the TCCM. Each switch position has a different resistance value. The TCCM monitors the voltage drop across MSS 4WD and MSS RTN circuits to determine switch position and thereby the operator's mode selection. The TCCM outputs VBATT (12v) circuit voltage on the MSS 4WD circuit.

When the TCCM detects an Open Circuit or Short to Ground, the TCCM will:

Ignore input from the MSS

Maintain current 4WD system mode

Set a DTC

Illuminate the Wrench Lamp and display Check 4x4 in the message center

If the fault is no longer detected, normal operation will resume on the next key cycle. The DTC will remain in continuous memory for 40 key cycles without a fault detected.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Conditions
P1812:00	4-Wheel Drive Mode Select Circuit Failure: No Sub Type Information	This DTC sets when the TCCM measures 12 volts across the MSS 4WD and MSS RTN circuits.
P1815:00	4-Wheel Drive Mode Select Short To Ground: No Sub Type Information	This DTC sets when the TCCM measures 0 volts across the MSS 4WD and MSS RTN circuits.

Possible Sources

Wiring, terminals or connectors
TCCM VBATT fuses
TCCM
MSS