System Description

WARNING: This page is about a different car, the 2015 Lexus IS 250 and 2014 Lexus IS 250. 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).

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 or gear, etc.).

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0751	Shift Solenoid "A" Performance (Shift Solenoid Valve S1)	[S1 stuck ON malfunction1:] The ECM determines there is a malfunction when the following conditions are both met. (2-trip detection logic) (a) When the ECM directs the gearshift to change to 1st gear, the actual gear is shifted to 2nd. (b) When the ECM directs the gearshift to change to 5th gear, the actual gear is also shifted to 5th. [S1 stuck OFF malfunction2:] The ECM determines there is a malfunction when the following conditions are both met. (2-trip detection logic) (a) When the ECM directs the gearshift to change to 5th gear, the actual gear is also shifted to 5th. (b) When the ECM directs the gearshift to change to 6th gear, the engine overruns (clutch slips).	[S1 stuck ON malfunction1:] Shift solenoid valve S1 remains open Valve body is blocked Automatic transmission (clutch, brake or gear, etc.) [S1 stuck OFF malfunction2:] Shift solenoid valve S1 remains closed Shift solenoid valve SLT remains open or closed Valve body is blocked No. 2 brake malfunction (Driving is difficult.) Automatic transmission (clutch, brake or gear, etc.)	Comes on	DTC stored

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P0751

Shift Solenoid "A" Performance (Shift Solenoid Valve S1)

[S1 stuck ON malfunction*1:]
The ECM determines there is a malfunction when the following conditions are both met. (2-trip detection logic)

(a) When the ECM directs the gearshift to change to 1st gear, the actual gear is shifted to 2nd.
(b) When the ECM directs the gearshift to change to 5th gear, the actual gear is also shifted to 5th.

[S1 stuck OFF malfunction*2:]
The ECM determines there is a malfunction when the following conditions are both met. (2-trip detection logic)

(a) When the ECM directs the gearshift to change to 5th gear, the actual gear is also shifted to 5th.
(b) When the ECM directs the gearshift to change to 6th gear, the engine overruns (clutch slips).

[S1 stuck ON malfunction*1:]

Shift solenoid valve S1 remains open
Valve body is blocked
Automatic transmission (clutch, brake or gear, etc.)

[S1 stuck OFF malfunction*2:]

Shift solenoid valve S1 remains closed
Shift solenoid valve SLT remains open or closed
Valve body is blocked
No. 2 brake malfunction (Driving is difficult.)
Automatic transmission (clutch, brake or 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
*1: Actual gear position under S1 stuck ON malfunction detected	2nd	2nd	3rd	4th	5th	6th
*2: Actual gear position under S1 stuck OFF malfunction detected	1st	1st	3rd	4th	5th	N*

*: Neutral

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
*1: Actual gear position under fail safe mode when S1 stuck ON malfunction	2nd	2nd	3rd	4th	5th	6th
*2: Actual gear position under fail safe mode when S1 stuck OFF malfunction	1st*3	1st*3	3rd	3rd	3rd	3rd

*3: Under engine braking downshifting to 1st or 2nd gear is prohibited.