Solenoid Valve BackUp Function

In the event that the shift solenoids malfunction, the ECU can still control the transmission by operating the remaining solenoid to put the transmission in a gear that will allow the vehicle to continue to run.

The chart below identifies the gear position the ECU places the transmission if a given solenoid should fail. Notice that if the ECU was not equipped with fail-safe, the items in parenthesis would be the normal operation. But because the ECU senses the failure, it modifies the shift pattern so the driver can still drive the vehicle. For example, if No. 1 solenoid failed, the transmission would normally go to overdrive in drive range first gear. But instead, No. 2 solenoid turned it on to give 3rd gear.

 RANGE NORMAL NO. 1 SOLENOID MALFUNCTIONING NO. 2 SOLENOID j BOTH SOLENOIDS MALFUNCTIONING MALFUNCTIONING Solenoid valve Gear Solenoid valve Gear Solenoid valve Gear Gear when shift lever is manually operated NO. 1 1 NO. 2 NO. 1 | NO. 2 NO. 1 1 NO. 2 "D" ON OFF 1st x I 0N x : (OFF) 3rd (O/D) ON x 1 1st O/D ON I ON 2nd X ON 3rd (ON) X O/D (1st) O/D OFF ON 3rd x I ON 3rd OFF 1 x 1 O/D O/D OFF OFF O/D x , OFF O/D OFF 1 x ! O/D O/D "2" ON OFF 1st X ON (OFF) 3rd (O/D) ON X 1st I 3rd* ON ON 2nd X ON 3rd (ON) X 3rd* (1st) 3rd* OFF ON 3rd X ON 3rd OFF X 3rd* 3rd* "L" ON OFF 1st X OFF 1st ON X 1st 1st ON ON 2nd X ON 2nd ON x j 1st 1st

( ): If no fail-safe function were provided x: Malfunctions

*0/D in the A540E, A540H

( ): If no fail-safe function were provided x: Malfunctions

*0/D in the A540E, A540H

Should both solenoids malfunction, the driver can still safely drive the vehicle by operating the shift lever manually.

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