Subject: ECM shift function of Toyota RAV 4’s and other models including Lexus with the U series transmission.
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ENTER CODE : ART30 AT CHECKOUT
The function of this system is as follows, in order to exhaust pressure from the direct clutch circuit, the ECM must provide voltage to SL2 solenoid, when voltage is removed, the direct clutch applies.
What happens in cases where the ECM begins to fail, voltage supplied to SL2 solenoid from the ECM begins to drop due to faults inside the ECM, most common being circuit board issues.
Although the factory specs indicate an 11 to 14 volt reading should be seen on this circuit, in all the testing we have done we never saw this amount of voltage. What we have seen in all cases is a 6.7 to 8.9 voltage range (figure 1). Most typical working systems will range in the 7.5 to 8.5 volts and work good.
Once the ECM has failed and can no longer supply the proper amount of voltage to the solenoid, direct clutch begins to partially apply, which is the reason we experience the bucking, binding sensation and high gear starts, and also set solenoid performance codes (not to be confused with solenoid circuit or electrical codes). Performance codes are no different then ratio codes for that matter.
To properly test this system, connect the positive voltmeter lead to the SL2 solenoid positive wire and the negative lead to SL2 negative wire at the ECM (figure 2). Then install a pressure gauge to direct clutch pressure port on the transmission (figure 3).
When the ECM has proper voltage, you will have a 0psi reading at pressure gauge. When voltage begins to drop under 5.0 volts to 4.5 volts, pressure will begin to slowly rise, the lower the voltage, the higher the pressure will rise.
The severity of symptoms on these vehicles will depend on how faulty the ECM function is, it has been our experience with these vehicles that there is no uniform failure, and although there may be vehicles with no codes or symptoms of high gear starts, bucking or binding, some ECM failures will be subtle and only cause intermittent complaint of 2-3 upshift flare or slide bump shift.
It is highly recommended to properly test the ECM, so as to ensure that a rebuilt transmission does not continue to fail without a known cause.
An excellent alternative to purchasing a new ECM from Toyota would be to look into Circuit Board Medics at www.circuitboardmedics.com.