QuestionTHANKS FOR YOUR RESPONSE BUT I DO NOT UNDERSTAND YOUR RECOMMENDATION OF REWIRING SOLENOID #1. I DID SAY ALL WIRING IS OK. I CAN APPLY 12VDC TO THE SOLENOID TERMINAL (ECU DISCONNECTED) AND HEAR THE SOLENOID ACTIVATE.
I AM CONVINCED IT IS THE NPS SWITCH IS INTERMITTENT. THIS IS THE 4TH DAY OF TROUBLE-FREE OPERATION SINCE TAKING ACTION 3.
IS THERE CRITICAL ALIGNMENTS INVOLVED IN REPLACING THE SWITCH? DO YOU HAVE ANY TRICKS THAT COULD SAVE TIME REPLACING THE SWITCH?
THANKS AGAIN - JACK
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-----Question-----
Auto: 1994 Camry V6 A541 Trans 175K+ miles
Symptom Will not downshift to 1st gear when stopped.
Occurrence: Intermittent problem.
When: Problem began in August 2005.
Trouble code P0753 –error is open or short on Shift Solenoid #1
Action #1 Replaced both solenoids 1 & 2.
Results No change
Action #2 Resistance and voltage measurements check good at ECU plug and transaxle plug with connectors on or off.
Action #3 Connected high-impedance monitors on solenoid #1 and #2 lines from the ECU to monitor the control voltages.
Results Solenoid #1 signal from ECU absent when problem is present. Indications are the transmission is in the “Fail Safe” mode. Can manually shift from low to third gear (low = both solenoids off, third = Solenoid #2 on), no second gear (both #1 and #2 solenoids are off).
Action #3 Rapidly moved the gearshift from low to park several times in an attempt to cause a cleaning action on the “Park/Neutral Position Switch.”
Reason: 40 years experience in electronics has proven all intermittent problems are caused by a faulty connection. The transaxle operates flawlessly when it does work.
Results Transaxle has operated properly for three days.
Question: Can the “Park/Neutral Position Switch” have a faulty (dirty) contact that prohibits sending the correct information to the ECU and in turn causes the ECU to command the transaxle to go into “Fail Safe Mode?”
Summary To date, no Toyota Authorized technician could recommend anything but replacing the transmission. Not an alternative: $2,000 plus work put into a $1,500 auto?!?!?
-----Answer-----
To answer your question. If the NPS is faulty, and not letting the ECU know you're in a gear position. The ECU will not take the steps to engage a gear.
Replace all the wiring from the #1 solenoid. You're up on electronics. The solenoid, trips off 9-14v, and needs a clean ground. Take some... Say 18ga wire. Soldier & heatshrink it to the correct wire off the stock ECU, run it inside the transmission & soldier / heat shrink it to the new solenoid.
The transaxles used go for around $300-700usd.
You can find the 1994 Camry manual on www.toyotanation.com
AnswerThen change the NPS switch. Don't yell.......
No there is nothing to change the NPS, a monkey could do it. Just go download that factory service manual.
On a side note, the ECU faults the solenoid based on only one criteria. That the resistance on each circuit to each individual solenoid is within a specified range. (around 15ohm) They can only trip & store specific solenoid codes if the resistance faults. Which means the wiring too, or that particular solenoid at the time the code was stored was faulty.
Intermittant wiring problems are fun.
