System Description

WARNING: This page is about a different car, the 2017 Lexus RC 350, 2017 Lexus RC 300, 2016 Lexus RC 350, 2016 Lexus RC 300, and 2015 Lexus RC 350. However, it is still accessible from the selected car via links, so may be relevant.

The ECM uses signals from the transmission revolution sensor (SP2) and transmission revolution sensor (NT) to detect the actual gear position (1st, 2nd, 3rd, 4th, 5th or 6th gear). Then the ECM compares the actual gear with the shift schedule in the ECM memory to detect mechanical problems of the shift solenoid valves, valve body or automatic transmission (clutch, brake, gear, etc.).

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0729	Gear 6 Incorrect Ratio	1. Diagnosis Condition 2. Malfunction Status 3. Malfunction Time 4. Other Engine coolant temperature is 40°C (104°F) or more and the vehicle is driven with the shift lever in D (no malfunctions are detected in the shift solenoid valve S1, S2, S3, S4, SR, SL1 and SL2, transmission revolution sensors (NT, SP2), coolant temperature sensor, knock control sensor, electronic throttle). Both of the following conditions (a) and (b) are met: When the ECM commands the transmission to shift to 5th gear, the actual gear is shifted to 5th. When the ECM commands the transmission to shift to 6th gear, the actual gear is shifted to 4th. 0.4 seconds 2-trip detection logic	Transmission valve body assembly is blocked or stuck (sequence valve) Shift solenoid valve SLT remains open or closed Automatic transmission with transfer assembly (clutch, brake, gear, etc.)	Comes on	DTC stored

HINT:

Gear positions in the event of a solenoid valve mechanical problem:

ECM commanded gear	1st	2nd	3rd	4th	5th	6th
Actual gear under malfunction	1st	2nd	3rd	4th	5th	4th

Gear position during fail-safe operation:

If any malfunction is detected, the ECM changes into the fail-safe mode to shift into the gear positions as shown in the table below.

Gear position under normal conditions	1st	2nd	3rd	4th	5th	6th
Actual gear under fail-safe mode	1st	2nd	3rd	3rd	3rd	3rd