The internal mode switch (Park/neutral switch/transmission range selector) relays your transmission gear selection to the TCM so it can set the appropriate line pressure. The P1823 DTC indicates that the P circuit in the internal mode switch has low voltage.
How Serious is the Code?
The transmission control unit has to know what gear you’ve selected, in order to set the appropriate line pressure for the clutches engage. Not having this information can cause extensive damage to these critical components.
Symptoms of a P1823 include:
- Excessively harsh gear changes
- Transmission cannot engage the correct gear
- PRNDL display stops working
- Limited torque converter operation
- Limp Mode
- Internal mode switch failure
- Shift cable damage or it’s out of adjustment
How to Diagnose the Code?
When diagnosing a P1823 diagnostic trouble code, the technician should first inspect the shift cable to ensure that it is not out of adjustment
What Repairs Will Fix P1823?
- Adjusting the shift cable
- Replacing the internal mode switch
P1819 – Internal Mode Switch – No Start\Wrong Range
P1820 – Internal Mode Switch Circuit A Low
P1821 – Internal Mode Switch Circuit B Low
P1822 – Internal Mode Switch Circuit B High
P1824 – Internal Mode Switch Circuit P High
P1825 – Internal Mode Switch Invalid Range
P1826 – Internal Mode Switch Circuit C High