Lost overdrive last week, no noises, just won't

Probably the transmission internal mode switch . But , without hooking up a scan tool an checking for DTC'S - diagnostic trouble codes an checking input data from the switch to the TCM - transmission control module i'd only be guessing . You don't want to waste money just replacing part's . Have a qualified repair shop check it out. Need factory service info an professional type scan tool .

Circuit/System Description
The transmission manual shift shaft switch assembly, also known as the Internal Mode Switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. The Park/Neutral Position (PNP) Switch is integrated into the IMS and connects to the Transmission Control Module (TCM) lead-frame through a short wire harness. The 5 inputs to the TCM from the transmission manual shift shaft switch assembly indicate the transmission gear selector lever position. This information is used for engine start enable, engine controls as well as determining the transmission shift patterns. The state of each input is available for display on the scan tool. The five input parameters represented are Signal A, Signal B, Signal C, Signal P (Parity), and Signal N (Park/Neutral Start Signal). Park/Neutral Signal is sent from the Park/Neutral switch directly to the Engine Control Module (ECM) and is used for engine start enable. The Park/Neutral Signal circuit is not connected to the TCM internally. The circuit uses the TCM as a pass-through connector only. The ECM Park/Neutral diagnostic monitors the Park/Neutral signal circuit to detect low voltage when the ECM expects high voltage and high voltage when the ECM expects low voltage.

DTC P1825: Internal Mode Switch - Invalid Range
DTC P182E: Internal Mode Switch - Invalid Range
DTC P1915: Internal Mode Switch Start/Wrong Range

Type 2011 suzuki kitashi code p1825 into Google and go to engine diagnostic code and it's all there for you , good luck colin

DTC P1819
Internal Mode Switch-No Start/Wrong Range

DTC P1825
Internal Mode Switch - Invalid Range

DTC P1826
Internal Mode Switch C Circuit High Voltage

The transmission internal mode switch (IMS) is a sliding contact switch attached to the selector detent inside the transmission side cover. The four inputs to the PCM indicate the position of the transmission range selector. The input voltage level at the PCM is high (B+) when the IMS is open and low when the switch is closed to ground. The four input parameters represented are Signals A, B, C and P (Parity). Refer to Transmission Internal Mode Switch Logic

Install a Scan Tool . A professional scan tool !
Turn ON the ignition, with the engine OFF.
Important: Before clearing the DTC, use the Scan Tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.
Record the DTC Freeze Frame and Failure Records.
Clear the DTC.
Select IMS on the Scan Tool .
Place the gear select lever in PARK range, then move to NEUTRAL range.
Does each range selected match the Scan Tool IMS display?
.Replace the lever assembly-manual shaft detent with internal mode switch.
Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

P1825

Transmission 4-Wheel Drive Clutch
Relay Open Circuit

P1826

Transmission 4-Wheel Drive Low Clutch
Relay Circuit To Battery hope it helps

P1744 - Torque Converter Clutch System Stuck in Off Position.

Either way the problem points to an internal transmission problem.
1. Drive it and see if the codes come back, and see if it is slipping in overdrive.

2. Check the transmission pressure in drive, with the overdrive on and the transmission slipping.

These transmissions have a high failure rate. Have seen internal transmission slippage that showed up in drive with the Overdrive (OD) switch on, but not with the OD switched off. It was related to the coasting clutch being on and off in that range. In that case, there was an internal mechanical transmission problem. We recommend a rebuilt transmission from the dealer and an external transmission cooler - the new rebuilt transmission will last longer.

Good luck (remember to rate this free answer).

These instrument clusters are known to be faulty.Replace cluster

Time for a rebuild or a new tranny, this one won't last much longer, sounds like there are bearings and clutches failing or failed already.

THAT IS THE OVERDRIVE IN THE TRANSMISSION
THE CAR MIGHT NOT WANT TO SHIFT TO HIGH GEAR OR OVERDRIVE SOME OF THESE CARS USE THE COMPUTER TO SHIFT IT TO OVERDRIVE AFTER IT GETS WARM THE THERMASTAT PLAYS A ROLL IN THAT WHEN THE ENGINE IS WARM THE LOOP IN THE COMPUTER CLOSES AND THE CAR WILL SHIFT TO HIGH/ OF THAT WON,T FIX IT THEN THE COMPUTER IS AT FAULT OR THE SENSOR IN THE TRANSMISSION IS BAD

I had this problem and dealer said I needed a new tranny. Took it for second opinion at local trans shop and they replaced the shift switch in the tranny for $250.

The code says tps switch so replace the throttle position sensor.